CA2144404C - Produce recognition system - Google PatentsProduce recognition system Download PDF
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- CA2144404C CA2144404C CA 2144404 CA2144404A CA2144404C CA 2144404 C CA2144404 C CA 2144404C CA 2144404 CA2144404 CA 2144404 CA 2144404 A CA2144404 A CA 2144404A CA 2144404 C CA2144404 C CA 2144404C
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- Expired - Fee Related
- G06—COMPUTING; CALCULATING; COUNTING
- G06K—RECOGNITION OF DATA; PRESENTATION OF DATA; RECORD CARRIERS; HANDLING RECORD CARRIERS
- G06K9/00—Methods or arrangements for reading or recognising printed or written characters or for recognising patterns, e.g. fingerprints
- G06K9/36—Image preprocessing, i.e. processing the image information without deciding about the identity of the image
- G06K9/46—Extraction of features or characteristics of the image
- G06K9/4642—Extraction of features or characteristics of the image by performing operations within image blocks or by using histograms
- G06K9/4647—Extraction of features or characteristics of the image by performing operations within image blocks or by using histograms summing image-intensity values; Projection and histogram analysis
- G07G—REGISTERING THE RECEIPT OF CASH, VALUABLES, OR TOKENS
- G07G1/00—Cash registers
- G07G1/0036—Checkout procedures
- G07G1/0045—Checkout procedures with a code reader for reading of an identifying code of the article to be registered, e.g. barcode reader or radio-frequency identity [RFID] reader
- G07G1/0054—Checkout procedures with a code reader for reading of an identifying code of the article to be registered, e.g. barcode reader or radio-frequency identity [RFID] reader with control of supplementary check-parameters, e.g. weight or number of articles
- G06—COMPUTING; CALCULATING; COUNTING
- G06K—RECOGNITION OF DATA; PRESENTATION OF DATA; RECORD CARRIERS; HANDLING RECORD CARRIERS
- G06K2209/00—Indexing scheme relating to methods or arrangements for reading or recognising printed or written characters or for recognising patterns, e.g. fingerprints
- G06K2209/17—Recognition of food, fruit, vegetables
The system includes an illumination source for illuminating the scene. By controlling the illumination source, an image processing system can take a first digitize image of the scene with the object illuminated a higher level and a second digitized image with the object illuminated at a lower level. Using an algorithm, the object(s) image is segmented from a background image of the scene by a comparison of the two digitized images taken. A processed image (that can be used to characterize features) of the object(s) is then compared to stored reference images. The object is recognized when a match occurs. The system can recognize objects independent of size and number and can be trained to recognize objects that it was not originally programmed to recognize.
-PRODUCE RECOGNITION SYSTEM
This invention relates to the field of recognizing (i.e., identifying, classifying, grading, and verifying) objects using computerized optical scanning devices. More specifically, the invention is a trainable system and method relating to recognizing bulk items using image processing.
BACKGROUND OF THE INVENTION
Image processing systems exist in the prior art for recognizing objects. Often these systems use histograms to perform this recognition. One common histogram method either develops a gray 15 scale histogram or a colour histogram from a (colour) image containing an object. These histograms are then compared directly to histograms of reference images. Alternatively, features of the histograms are extracted and compared to features extracted from histograms of images containing reference objects.
20 The reference histograms or features of these histograms are typically stored in computer memory. The prior art often performs these methods to verify that the target object in image is indeed the object that is expected, and, possibly, to grade/classify the object according to the quality of its appearance relative to the referencc histogram. An alternative purpose could be to identify the target object by comparing the targel image object histogram to the histograms 25 of a number of reference images of objects.
In this description, identifying is defined as determining, given a set of reference objects or classes, which reference object the target object is or which reference class the target object belongs to. Classifying or grading is defined as determining that the target object is known to 2l4~4e4 -be a certain object and/or that the quality of the object is some quantitatively value. Here, one of the classes can be a "reject" class, meaning that either the quality of the object is too poor, or the object is not a member of the known class. Verifying, on the other hand, is defined as determining that the target is known to be a certain object or class and simply verifying this to 5 be true or false. Recognizing is defined as identifying, classifying, grading, and/or verifying.
Bulk items include any item that is sold in bulk in supermarkets, grocery stores, retail stores or hardware stores. Examples include produce (fruits and vegetables), sugar, coffee beans, candy, nails, nuts, bolts, general hardware, parts, and package goods.
In image processing, a digital image is an analog image from a camera that is converted to a discrete representation by dividing the picture into a fixed number of locations called picture elements and quantizing the value of the image at those picture elements into a fixed number of values. The resulting digital image can be processed by a computer algorithm to develop other 15 images. These images can be stored in memory and/or used to determine information about the imaged object. A pixel is a picture element of a digital image.
Image processing and computeI vision is the processing by a computer of a digital image to modify the image or to obtain from the image properties of the imaged objects such as object 20 identity, location, etc.
An scene contains one or more objects that are of interest and the surroundings which also get imaged along with the objects. Thcse surroundings are called the background. The background is usually further away from the camera than thc object(s) of interest.
Segmenting (also called figure/ground separation) is separating a scene image into separate object and background images. Segmenting refers to identifying those image pixels that are contained in the image of the object versus those that belong to the image of the background. The segmented object image is then the collection of pixels that comprises the object in the original -image of the complete scene. The area of a segmented object image is the number of pixels in the object image.
Illumination is the light that illuminates the scene and objects in it. Illumination of the whole 5 scene directly determines the illumination of individual objects in the scene and therefore the reflected light of the objects received by imaging apparatus such as video camera.
Ambient illumination is illumination from any light source except the special lights used specifically for imaging an object. For example, ambient illumination is the illumination due to 10 light sources occurring in the environment such as the sun outdoors and room lights indoors.
Glare or specular reflection is the high amount of light reflected off a shiny (specular, exhibiting mirror-like, possibly locally, properties) object. The colour of the glare is mostly that of the illuminating light (as opposed to the natural colour of the object).
A feature of an image is defined as any property of the image, which can be computationally extracted. Features typically have numerical values that can lie in a certain range, say, R0 - R1.
In prior art, histograms are computed over a whole image or windows (sub-images) in an image.
A histogram of a feature of an image is a numerical representation of the distribution of feature 20 values over the image or window. A histogram of a feature is developed by dividing the feature range, R0 - R1, into M intervals (bins) and computing the feature for each image pixel. Simply counting how many image or window pixels fall in each bin gives the feature histogram.
Image features include, but are not limited to, colour and texture. Colour is a two-dimensional 25 property, for example Hue and Saturation or other colour descriptions (explained below) of a pixel, but often disguised as a three-dimensional property, i.e., the amount of Red, Green, and Blue (RGB). Various colour descriptions are used itl the prior art, including: (I) the RGB
space; (2) the opponent colour space; (3) the Munsell (H,V,C) colour space; and, (4) the Hue, Saturation, and Intensity (H,S,I) space. For the latter, similar to the Munsell space, Hue refers to the colour of the pixel (from red, to green, to blue), Saturation is the "deepness" of the colour (e.g., from greenish to deep saturated green), and Intensity is the brightness, or what the pixel would look like in a gray scale image.
5 Texture, on the other hand, is an visual image feature that is much more difficult to capture computationally and is a feature that cannot be attributed to a single pixel but is attributed to a patch of image data. The texture of an image patch is a description of the spatial brightness variation in that patch. This can be a repetitive pattern (of texels), as the pattern on an artichoke or pineapple, or, can be more random, like the pattern of the leaves of parsley. These are called 10 structural textures and statistical textures, respectively. There exists a wide range of textures, ranging from the purely deterministic arrangement of a texel on some tessellation of the two-dimensional plane, to "salt and pepper" white noise. Research on image texture has been going on for over thirty years, and computational measures have been developed that are one-dimensional or higher-dimensional. However, in prior art, histograms of texture features are 15 not known to the inventors.
Shape of some boundary in an image is a feature of multiple boundary pixels. Boundary shape refers to local features, such as, curvature. An apple will have a roughly constant curvature boundary, while a cucumber has a piece of low curvalure, a piece of low negative curvature, and 20 two pieces of high curvature (the cnd points). Other boundary shape measures can be used.
Some prior art uses colour histograms to identify objects. Given an (R,G,B) colour image of the target object, the colour representation used ror the histograms are the opponent colour: r~ =
R - G, bY = 2 * B - R - G, and wb = R + G + B. The wb axis is divided into 8 sections, 25 while r.~ and by axes are divided into 16 section~. This results in a three-dimensional histogram of 2048 bins. This system matches target image histograms to 66 pre-stored reference image histograms. The set of 66 pre-stored reference image histogram is fixed, and therefore it is not a trainable system, i.e., unrecognized target images in one instance will not be recognized in a later instance.
U.S. Patent 5,060,290 to Kelly and Klcin discloscs the grading of almonds based on gray scale histograms. Falling almonds are furnished with uniform light and pass by a linear camera. A
gray scale histogram, quantized into 16 levels, of the image of the almond is developed. The histogram is normalized by dividing all bin counts by 1700, where 1700 pixels is the size of the 5 largest almond expected. Five features are extracted from this histogram:
(1) gray value of the peak;
(2) range of the histogram;
(3) number of pixels at peak;
(4) number of pixels in bin to the right of peak; and, (5) number of pixels in bin 4.
Through lookup tables, an eight digit code is dcveloped and if this code is in a library, the almond is accepted. The system is not trainable. The appearances of almonds of acceptable quality are hard-coded in the algorithm and the system cannot be trained to grade almonds 15 differently by showing new instances of almonds.
U.S. Patent 4,735,323 to Okada et al. discloses a mcchanism for aligning and transporting an object to be inspected. The system morc specif~lcally relates to grading of oranges. The transported oranges are illuminated with a light within a predetermined wavelength range. The 20 light reflected is received and converted into an elcctronic signal. A level histogram divided into 64 bins is developed, where Level = (the intensity of totally rcflccted light) /
(the intensity of grecn light reflccted by an orange) The median, N, of this histogram is dctermined and is considcrcd as representing the colour of an orange. Based on N, the orange colouring can bc classificd into four grades of "excellent"
"good", "fair and "poor" or can be graded rlner. The system is not trainable, in that the appearance of the different grades of oranges is hard-codcd into the algorithms.
214~04 -The use of gray scale and colour histograms is a vcry effective method for grading or verifying objects in an image. The main reason ror this is that a histogram is very compact representation of a reference object that does not depend on the location or orientation of the object in the mage.
However, for image histogram-based recognition to work, certain conditions have to be satisfied.
It is required that:
(1) the size of the object in the image is roughly known, (2) there is relatively little occlusion of the object (i.e., most of the object is in the image and not obscured by other objects), (3) there is little difference in illumination of the scene of which the images (reference and target images) are taken from which the reference object histograms and target object histograms are developed, and (4) the object can be easily segmented out from the background or there is relatively little distraction in the background.
Under these conditions, comparing a target object image histogram with reference object image histograms has been achieved in numerous ways in the prior arl.
Some prior art matching systems and methods, claim to be robust to distractions in the background, variation in viewpoint, occlusion, and varying imagc resolution. However, in some of this prior art, lighting conditions are not controllcd. The systems fail when the colour of the 25 illumination for obtaining the reference object histograms is different from the colour of the illumination when obtaining the target object image histogram. The RGB values of an image point in an image are very dependent on the colour of the illumination (even though humans have little difficulty naming the colour given the whole image). Consequently the colour histogram of an image can change dramatically when the colour of the illumination (light - 214~404 frequency distribution) changes. Furthermore, in these prior art systems the objects are not segmented from the background, and, therefore, the histograms o the images are not area normalized. This means the objects in target images have to be the same size as the objects in the reference images for accurate recognition because variations of the object size with respect 5 to the pixel size can significantly change the colour histogram. It also means that the parts of the image that correspond to the background have to be achromatic (e.g. black), or ,at least, of a colouring not present in the object, or they will significantly perturb the derived image colour histogram.
Prior art such as that disclosed in U.S. Patent 5,060,290 fail if the size of the almonds in the image is drastically different than expected. Again, this is because the system does not explicitly separate the object from its background. This system is used only for grading almonds: it can not distinguish an almond from (say) a peanut.
Similarly, prior art such as that disclosed ;n U. S. Patent 4,735,323 only recognizes different grades of oranges. A reddish grapefruit might very well be deemed a very large orange. The system is not designed to operate with more than one class of fruit at a time and thus can make do with weak features such as the ratio of green to white reflectivity.
In summary, much of the prior art in the agricultural arena, typified by U.S. patents 4,735,323 and 5,060,290, is concerned with classifying/grading produce items. This prior art can only classify/identify objects/products/produce if they pass a scanner one object at a time. It is also required that the range of si~es (from smallest to largest possible object size) of the object/product/produce be known beforelland. These systems will fail if more than one item is scanned at the same time, or to be more precise, if more than one object appears at a scanning position at the same time.
Further, the prior art often requires carefully engineered and expensive mechanical environment with carefully controlled lighting conditions where the items arc transported to predefined spatial - 2144~04 loeations. These apparatuses are designed specifically for one type of shaped objeet (round, oval, ete.) and are impossible or, at least, not easily modified to deal with other object types. The shape of the objects inspires the means of object transportation and it is impossible or difficult for the transport means to transport different object types. This is especially true for oddly 5 shaped objeets like broeeoli or ginger. This, and the use of features that are speeif1eally seleeted for the partieular objects, does not allow for the prior art to distinguish between types of produee.
Additionally, none of the prior art are trainable systems where, through human or computer 10 intervention, new items are learned or old items disearded. That is, the systems can not be taught to reeognize objeets that were not originally programmed in the system or to stop reeognizing objeets that were originally programmed in the system.
One area where the prior art has failed to be effeetive is in produee check out. The eurrent 15 means and methods for eheeking out produee poses problems. Affixing (PLU - priee lookup) labels to fresh produee is disliked by eustomers and produee retailers/wholesalers. Pre-paekaged produee items are disliked, beeause of increased cost of packaging, disposal (solid waste), and inability to inspeet produce quality in r~re-packaged form.
20 The process of produee cheek-out has not changed mueh since the first appearance of grocery stores. At the point of sale (POS), the cashier has to recognize the produce item, weigh or count the item(s), and determine the priee. Currently, in most stores the latler is achieved by manually entering the non-mnemonic PLU code that is associated with the produce. These codes are available at the POS in the form of printed list or in a booklet with pictures.
Multiple problems arise from this proeess of produee eheck-out:
(I) Losses incurred by the store (shrinkage). First, a cashier may inadvertently enter the wrong eode number. If this is to the advantage of the eustomer, the eustomer will be less motivated to bring this to the attention of the cashier. Seeond, for friends and relatives, the 2144~~
cashier may purposely enter the code of a lower-priced produce item (sweethearting).
(2) Produce check-out tends to slow down the check-out process because of produce identification problems.
(3) Every new cashier has to be trained on produce names, produce appearances, and PLU
OBJECrS OF THE INV~NTION
10 An object of this invention is an improvcd apparatus and mcthod for recognizing objects such as produce.
An object of this invention is an improved trainable apparatus and mcthod for recogni7ing objects such as produce.
Another object of this invention is an improved apparatus and method for recognizing and pricing objects such as producc at the point of sale or in the produce department.
A further object of this invention is an improvcd means and method of user interface for 20 automated product identification, such as, produce.
SUMMARY OF THE INVENTION
The present invention is a systcm and apparatus thal uses image processing to recognize objects 25 within a scene. The system includes an illumination sourcc for illurninating the scene. By controlling the illumination source, an image processing system can take a first d}gitized image of the scene with the object illuminated at a higher Ievel and a second digitized image with the object illuminated at a lower level. Using an algorithm, thc object(s) image is novelly segmented from a background image of the scenc by a comparison of the two digitized images taken. A
`~ 214~404 YO9-94-056 l 0 processed image (that can be used to characterize features) of the object(s) is then compared to stored reference images. The object is recognizcd when a match occurs.
Processed images of an unrecognized object can be labelled with identity of object and stored in memory, based on certain criteria, so that the unrecognized object will be recognize when it is imaged in the future. In this novel way, the invention is taught to recognize previously unknown objects.
Recognition of the object is independent of the size or number of the objects because the object image is novelly normalized before it is compared to the reference images.
Optionally, user interfaces and apparatus that detcrmines other features of the object (like weight) can be used with the system.
BRIEF DESCRIPTION OF THE DRAWINGS
~igure 1 is a block diagram of the one preferred embodiment of the present system.
Figure 2 is a flow chart showing on preferred embodiment of the present method for recogni7ing objects.
Figure 3 illustrates segmenting a scene into an object image and a background image.
Figure 4 is a block diagram of a prcferrcd embodiment of apparatus for segmenting images and recogni7ing object in imagcs.
Figure 5 is a flow chart of a prefcrred mctho(l for segmcnting target object images.
Figure 6 is a flow chart showing a prefcrrcd mcthod of character;zing reference to target object feature(s).
Figure 7 is a flow chart showing a prefcrrcd method for (area/length) normalization of object feature(s) characterization.
Figure 8 illustrates the comparison of an area/length normalized target object characterization to one or more area normalizcd referencc object characterizations.
2144~04 YO9-94-056 l I
Figure 9 is a flow chart showing a preferred (algorithmic) method of the present apparatus to recognize new images.
Figure 10 is a block diagram showing multiple features of an object being extracted.
Figure 11 is a flow chart showing the histogramming and normalizing of the feature of 5 texture.
Figure 12 is a flow chart showing the histogramming and normalizing of the feature of boundary shape.
Figure 13 is block diagram showing a weighing device.
Figure 14 shows an image where the segmented object has two distinct regions determined 10 by segmenting the object image and where these regions are incorporated in recognition algorithms.
Figure 15 shows a human interface to the present apparatus wh;ch presents an ordered ranking of the most likely identities of the produce being imaged.
Figure 16 shows a means for human determination of the identity of object(s) by browsing 15 through subset(s) of all the previously installed stored icon images and the means by which the subsets are selected.
Figure 17 is a preferred embodiment of the present invention using object weight to price object(s).
The apparatus 100 shown in Figure I is one prcferred embodiment of the present invention that uses image processing to automatically recognize OllC or more objects 131.
25 A light source 110 with a light frcqucncy ~istrib-ltion that is constant over time illuminates the object 131. The light is non-monochromatic and may include infra-red or ultra violet frequencies.
Light being non-monochromatic and of a constant frequency distribution ensures that the colour appearance of the objects 131 does not change due to light variations between different images taken and that stored images of a given object can be matched to images taken of that object at 21~404 YO9-94-056 l 2 a later time. The preferred lights are flash tubes Mouser U-4425, or two GETM cool-white fluorescent bulbs (22 Watts and 30 Watts), GE FC8T9-CW and GE FC12T9-CW, respectively.
Such light sources are well known.
5 A video input device 120 is used to convcrt the reflected light rays into an image. Typically this image is two dimensional. A preferred video input device is a colour camera but any device that converts light rays into an image can be used. These cameras would include CCD camera and CID cameras. The colour camera output can be RGB, HSI, YC, or any other representation of colour. One preferred camera is a Sony~ card-camera CCB-C35YC or Sony XC-999. Video 10 input devices like this 120 are well known.
Colour images are the preferred sensory modality in this invention. However, other sensor modalities are possible, e.g., infra-red and ultra-violet images, smell/odour (measurable, e.g., with mass spectrometer), thermal decay properties, ultra-sou nd and m agnetic resonance images, DNA, 15 fundamental frequency, stiffness and hardness. These modalities can be enabled with known methods of illuminating, measuring, or taking samples of the object 13l and with a compatible imaging device 120 for creating the image.
The object 131 is the object being imaged alld recognized by the system 100. The object 131 can 20 comprise one or more items. Although it is preferred that objects 131 be of one type (variety), e.g., one or more apples, thc items can bc of dirfercnt typcs, e.g., a cereal box (Object A) and an apple (Object B). System 100 will thel1 recognize objects as either as (1) Object A, (2) Object B, (3) both Object A and Object B, or, (4) reject objects as unrecognizable. The object(s) can be virtually anything that can be imaged by lhe system 1()(), however pref~rred objects 131 are bulk 25 items including produce (fruits and vegetables), hardware, boxed goods, etc.
A calculating device 140, typically a computer 140, is used to process the image generated by the video input device 120 and digitized (to be compatible with the computer 140) by a frame grabber 142.
The processing is performed by an algorithm 200. Othcr calculating devices 140 include: personal computers, and workstations. The calculating device 140 can also be one or more digital signal processors, either stand-alone or installed in a computer. It can also be any special hardware capable of implementing the algorithm 200. A preferrcd embodiment is a Datatranslation DSP
board DT 2878 coupled to a Datatranslation DT 2871 frame grabber board residing in an IBM
ValuePointTM computer, or in the IBM 4~906~ series of POS Cash Registers. The frame grabber 142 is a device that digitizes the image signal from the camera 120. If the camera 120 is a digital camera then a separate frame grabber 142 may not be required. The digitizer may be separate from the computer 140 or an integrated part of it. The image may be stored in a standard memory device 144. Given this disclosurc, one skilled in thc art could develop other equivalent calculating devices 140 and frame grabbers 142.
An optional interactive output dcvice 160 can be connected to the calculating device 140 for interfacing with a user, like a cashier. The output device 160 can include screens that assist the user in decision making 164 and can also provide mechanisms to train 162 system 100 to recognize new objects. An optional weighing device 170 can also provide an input to the calculating device 140 about the weight (or density) of the object 131. See description below (Figure 13).
Figure 2 is a flow chart of the algorithm 200 run by the calculating device, or computer 140. In step 210, a target object to be recognized is imaged by camera 120. Imaging like this is well known. The image of target object 131 is then novelly segmented 220 from its background. The purpose of step 220 is to separate the target object 131 from thc background so that the system 100 can compute characteristics of separated objcct 131 imagc pixels independently of the background of the scene. In step 23() onc or morc features of the object 131 can be computed, preferably pixel by pixel, from the segmented object image. In step 240, characterizations of these pixel-by-pixel computed feature sets are developed. Normalizing, in step 250, ensures that these characterizations do not depend on the actual area, léngth, size, or characteristics related to area/length/size that the object(s) 131 occupy in the image, so that one or multiple instances of - 21~4104 object 131 are recognized as same object type. Preferred means of normalizing the characterization by the segments occupied by objects 131 in the image is achieved by counting the number of times feature characteristic(s) are computed. (This is descr;bed further in Figure 7. The preferred means of normalizing is by area or by length.) In step 260 the 5 count-normalized characterization of the target object is compared with the count-normalized characterizations of reference objects, which are stored in memory storage 270. The storage 270 may be located in the storage device 144 or computer 140. (See the description in Figure 8.) In step 251 area-normalized characterizations are stored, depending on certain criteria 255 in computer memory 270. This step enables the system 100 to be trained, since the storage criteria 255 might permit storage 251 of new reference images which can later be compared to target 131 images. (See the description of Figure 15.) Step 220 is the segmenting or separating of the object image from the background image. This step is performed so that the features of the target object can be processed independently of the 15 effects and disturbances of the background of the scene. Figure 3 illustrates two preferred methods (Figure 3a and Figure 3b, respectively) that segment the object image from the background image.
Figure 3a shows two scenes. The first imaged scene 310, shows an image of a background 311 20 without any other objects present in the field of view of camera 120. The second imaged scene 320 includes both an image of the sccne background 311 and an image 130 of one or more objects 131. Here the pixels of the imaged object 130 replace pixels in the background image 311 in those areas of the scene image 32() where object 131 is present. Hence, it is an image of background 311 with instances of objects 131 present in the scene.
A comparison of the scenes 3lO and 320, preferably on a pixel by pixel basis, allows the object image 130 to be segmented (separated out) from the background image 311 of the scene. If for a given pixel in the 320 image, the brightness is different from (e.g., more then) the image brightness of same pixel in 310, this pixel belongs to object image 130. If for a given pixel in the - 214~404 YO9-94-056 t 5 image 320, the brightness is equal to same pixel in 310, this pixel belongs to background image 311. (See the description of Figure 5).
Figure 3b shows two images of a scene with a background and one or more objects produced by a preferred embodiment of this invention that enables segmentation of the object image. Image 330 in Figure 3b is an image of a scene (including objects 131 and a background 311) with light source 110 off. That is, the scene image 330 consist of an image of background 311 illuminated by ambient light. Also in the scene image 330 are the object images 135 obscuring the background. Because the light source 110 is off, object images 13S appear dark in scene image 330 because they are not illuminated by the light source I tO.
Image 340 in Figure 3b is an image of the scene with light source 110 on. In this case, the light source 110 illuminates objects 131 in field of view of camera with an amount of light greater than ambient light. This results in the object images 130 being brighter (than in 330) in scene image 340.
Figure 4 is a block diagram showing a preferred system 400 for imaging scenes (such as those described in Figure 3), segmenting object images 130 from their background image 311 of the physical background 312, and recognizing object(s) 131.
The preferred system 400 places the object 131 above light 110 and camera 120, thus providing images of object 131 looking up from below. The system 400 provides a support 405 for the object 131 and also ensures that object is of rlxed an<l repeatable distance 407 from camera 120.
In addition, the system 400 allows imaging of shiny object (like a plastic bag) with reduced glare (specular reflections) in the image by providing a filtering system comprised of 410 and 420.
The system 400 comprises an opaque enclosure 401 for the light 110 and camera 120. The enclosure has a single opening 403 facing the object 131. The opening 403is of a sufficient size to allow the object 131 to be imaged by the camera 120 and illuminated by the light 110. The - 2i~l0~
opening can be square, round or any other shape. A transparent surface 405 covers the opening 403 in the enclosure 401. This surface 405 could be a sheet of glass. The transparent surface 405 provides a support on which the imaged object 131 can be placed. By placing the object 131 on the surface 405, the distance 407 between camera 120 and object 131 remains fixed thus 5 providing the means for repeatable imaging.
To remove glare from image of object 131 (from object 131 itself and possibly a surrounding plastic bag) a polarizing filter 420 is incorporated with the lens of camera 120 or placed just above the lens of the camera 120. A second polarizing filter 410 is placed between the light 110 and the opening 403. This insures that the light reaching the object 131 is polarized.
Alternatively, the light may be completely enclosed by the polarizer. If the light is partly enclosed in a box (such as a camera flash) or by a reflector (such as a photographic spotlight) the polarizer needs to be placed only on the opening in the light assembly which allows the light through. The direction of the polarization in first filter 410 is orthogonal to the direction of polarization in second filter 420. It is well-known from prior art that specular reflection reflected off an object (such as object t31) is polarized as opposed to the diffuse (matte) reflection reflected off the object. Imaging object 131 with a polarizing filter 420 thus reduces glare in image. Fiurther, illuminating 131 with light 110 polarized by 410 reduces the amount of glare on object 131. 410 also ensures that the polarization angle of the reflected specular light, off object 131 is orthogonal to polarizer 420. Hence, imaging object 131 through polarizer 420 which is orthogonal to polarizer 410 further reduces ~he amount of glare in object image 130.
A light Control 450 switches the light 110 on and Orr, or switches light 110 between different intensity levels. The control 450 may be implementcd on the computer 110 or be connected 2S directly to the light 110 or may be a separate devicc. The control may be a part of the light 110 as a timing device such as in a strobe. The control may be synchronized with the camera or the computer or both. Light switching controls 450 are well known.
The segmenting step 220 of Figure 2 is further described in Figure 5, which shows a preferred 21~4~04 method for segmenting the object image from the scene.
In step 510, an image (a first image) of the scene is produced with the light 110 switched on, or at a higher intensity, so as to illuminate object 131 properly. Control 450 controls the light 110 S switching.
In step 520, a second image of the scene is produced with the light 110 switched off or set to a level below the level in step 510. The setting of the light 110 should be such that the object 131 appears darker in the second image than in the first image. By performing these novel steps, the object image 130 can be separated or segmented from the background image 311 in the steps below.
Further, the object 131, the background 312, and the image input device 120 should be at the same position in both step 510 and 520 to assure that the first and second images are in spatial registration. Suppose each pixel is numbered starting in the upper left corner of the image then proceeding across the first line then down to the second line in the manner of reading a book.
Registration means that each numbered pixel in the first image corresponds to the same area of the scene (object(s) 131 and backgrouncl 312) as the identically numbered pixel in the second image. Proper registration can be ensured by either acquiring the rlrst and second image in quick succession, or by imaging a stationary object 131 against a stationary background 31~.
The order of acquiring the first and second image may be reversed; that is, step 520 can be performed before step 510.
In step 530 of the algorithm 220, the first and second images are digitized in the frame grabber 142. In the computer 140, each and every pixel in the first digitized image is compared to the respective pixel at the same location in the second digitized image. Pixel by pixel comparisons such as this are known in the image processing art. For example, although the pixels in each pair being compared must correspond to one another (i.e., be in the same respective location in 2144~04 each image), the corresponding pixel pairs in the images can be compared in any order. Further, alternative comparisons can be made, e.g., comparing ever second or third pixel.
In step 540, a check is performed on a pixel by pixel basis to determine if a pixel in the first 5 image is brighter than the corresponding pixel in the second image by more than a value T. In any pixel comparison, if the pixel in the first image pixel is brighter than its corresponding pixel in the second image by more than T, the algorithm 220 takes the branch 542 and designates this pixel as corresponding to the object 131. Likewise, if the p;xel comparison shows that the pixel in the first image is not brighter than its corresponding pixel in the second image by more than the value T, the algorithm 220 takes the branch 544 and designates this pixel as corresponding to the image 311 of physical background 312.
The value of tolerance T may be a constant. A preferred tolerance T is 5% of the largest image intensity. Alternatively, the value of T may vary depending on the positions of pixels in the 15 image or depending on the intensity of the pixel in the dark image. The positional variation of T allows the system to compensate for uneven illumination from source 110. The dark intensity variation of T allows the system to correctly identify foreground objects with low reflectivities (such as black objects). The value T may be fixed or may be recomputed from time to time by the system. It might, for instancc, be necessary to change the value of T as light source 110 ages 20 or changes in intensity for some other reason (such as a variation in the AC line voltage supplied to the bulb). This recomputation could be performed on a pair of images of the background with no object (one image of the background 312 highly illuminated and one less so). Since no object is present, both background images shoukl appear to be illuminated the same amount (with ambient light). However, in practice, the light 110 might illuminate the background 312 slightly 25 when the light is switched to a higher intensity. Therefore a tolerance T is chosen for the comparison of the corresponding pixel pairs. The tolerance T could then be set so that only a very small number of pixels in this pair of background images actually passes the test. For example, in a preferred embodiment, T would be set so that fewer than 10% of the pixel pairs differ in illumination more than the tolerance T.
- 21~4404 In a preferred embodiment, the steps 530 and 540 are performed on a pixel by pixel basis for each pixel location in the scene image. The result is that the pixels corresponding to the object 131 are collected in a segmented object image t30. Specifically, in the segmented object image, all pixels from the first image that are substantially brighter than their corresponding pixel in the 5 second image are collected in segmented object image at the position they were in the first image.
Therefore, the segmented object image corresponds to the desired image of the object 131 removed from the background 3t2. If needed, the remaining pixels in the image (e.g., the pixels not corresponding to the object 130) can be assigned any desired value and/or can be further processed using known image processing techniques.
In like manner, the pixels corresponding the background 312 are collected in a segmented background image 311. Specifically, all pixels from the rlrst image that are not substantially brighter than the corresponding pixel in the second image are collected in the segmented background image at the position they were in the rlrst image. (In a preferred embodiment, 15 "substantially brighter" means that the difference in illumination between the pixels in the corresponding pixel pair is greater than the tolerance, T.) The segmented background image corresponds to the image of the background 311 with the object 130 removed. If needed, the remaining pixels in the segmented background image (i.e., those corresponding to the removed object pixel locations) can be assigned any desired value and/or further processcd using known 20 image processing techniques.
If only the image of the object 13() is desired, steps 544 to obtain 311 need not be performed.
Similarly, if only the image of the background 312 i~ desired, steps 542 and 130 need not be performed.
In an alternative preferred embodiment, a translucent part of the object 131 (for example, a plastic cover~ may be separated from an opaque part of the object 131, by adding steps 552, 554, and 556.
2144~04 In this embodiment, branch 542 goes to step 552 instead of step 540. Before step 552, it has been determined already that the pixel in the first image is brighter than its corresponding pixel in the second image. Step 552 determines if the object 130 pixels of the second image (the object 131 under low illumination) are brighter than a value V, a second tolerance value. If so, 553 not in drawing RMB 4/23 branch 553 is taken and the object pixel belongs to the translucent part 554 of object 130. (The object is translucent at this pixel location since some ambient light passed through the object 130 and was imaged at this location when the light 110 was switched to low illumination.) 555 not in drawing RMB 4/23 If not, then branch 555 is taken and the pixel belongs to opaque part 556 of object 130. (No ambient light, or an amount below the tolerance, V, is measured through the opaque part of the object 130.) The value V may be constant for each pixel in the second image or may be variable, depending, for example, on the position on the pixel in the second image. Note that the value, V, may further be computed as deseribe above, from an image of the background 135 alone, by choosing a V such that 95% to 85% of the background image is brighter than V. A preferred value for V is 20% of the brightest image intensity.
In step 554, a translucent object image is created. In this step, each pixel in the first image (which belongs to the object) which corresponds to a pixel in the second image that is brighter than the value V, corresponds a translucent part of object 130 and is stored in a translueent objeet image. After all pixels of the r1rst and seeoncl images are so proeessed, the translucent objeet image will contain only the image of the translueent parts of objeet 130. If needed, the remaining pixels of the translucent object image may be assigned any desired value and/or processed further.
In step 556, an opaque object image is created. In this step, each pixel in the ~Irst image (which belongs to the object) which corresponds to a pixel in the second image equal to or darker than the value V, corresponds to an opaque part of objeet image 130 and is stored in the opaque object image 556. After all pixels of the first and second images are so processed, the opaque objeet image will eontain only the image of the opaque parts of objeet 130. If needed, the `~ 214~404 remaining pixels of the opaque object image may be assigned any desired value and/or be further processed.
If only an image of the opaque parts of the object 130 is desired, step 554 need not be 5 performed. Similarly, if only an imagc of the translucent parts of the object 130 is desired, step 556 need not be performed.
In another preferred embodiment, step 552 is combincd with step 540 and steps 542 and 130 are removed. This results in the translucent object image or the opaquc object image (or both) but 10 not the complete segmented object image 130.
Other combinations of steps 552, 554 and 556 with thc previous steps are within the contemplation of this invention.
15 After the image is segmented 220, a computation of one or more target object features is performed. Refer to step 230 of Figure 2. The computation 230 is performcd by the computer 140 and is used to determine features of the target objcct. This determination is made by novelly performing this step 230 only on the ~eparated out (segmented) image 130 of the target object obtained in step 220. For each pixel in the scgmented object image, features are determined. For 20 example, such features can be computc<l using the colour of a single pixel, or using the (colour) value of a pixel and the ~colour) values of its surrounding pixels. Features include, but are not limited to, colour, shape, texture, densit~ of the scgmcntcd imagc of target object. Normally, the feature(s) are represented by onc or more fcature valucs.
Once one or more features are dctermincd 230, thc fcature or sct of features is characterized 240.
Histogramming is a preferred way of doing thc charactcrization 240. See the description of Figure 6 below. However, other method~ of characterizing feature(s) can be used. For example, median feature value, first order (mean value) ancl/or highcr ordcr statistics of computed feature values, or any statistic that can bc derived from thc computed sct of feature values can be used.
Given this disclosure, one skilled in the art could develop other equivalent ways to characterize features.
The normalization step 250 of the algorithm 200 is a novel step for making the characterized S feature(s) of an object independent of the size of the actual object 131 being imaged. This step also enables one or multiple instances of object 131 to be recognized by the apparatus 100 independent of the number of objects 131, or size of objects 131, in the scene. Normalization 250 is performed on one or more of the computed feature characterization(s). A preferred method of normalization can be done with respect to area or Iength, e.g., obtained by counting number 10 of pixels in segmented object image (see the description of Figure 7, below) or by counting number of pixels on boundary of segmented object image (see the description of Figure 12, below).
Other methods of normalization, e.g., normalizing with respect to any other characteristic derived 15 from segmented object image, are also within the contemplation of the invention.
Another novel feature of the present invention enables the system 100 to be trained. If a normalized characterization of an object 131 is not recognized, i.e., not matched with reference information (step 260), the normalized characterization is checked 251 if it satisfies some storage 20 criteria 255. If the normalized characterization of the unrecognized object meets the storage criteria 255, it will be stored 270 along with the other reference information. Therefore, the next time this object 131 is imaged by the system 100, it will be matched to a reference image and recognized. See the description of Figure 9 below. Training allows the system 100 to be able to recognize objects that the system is not "hard-wirc(l" (prc-programmed) to recognize, thus making 25 the system more flexible. The stored characterization is normalized so that the number of objects 131 used for reference characterization can be different from number of objccts 131 used for developing target characterization.
Storage criteria can include any criteria established by the system 100 design. The ability to select and/or create storage criteria 255 can also he given to a user through an interface 160. A
simple storage criteria might be to store any information provided about an unrecognized object in the reference database 270. Other storage criteria might include, but are not limited to:
(1) the quality of image 210 is good;
(2) a large percentage of target object occupies image 210;
(3) characterizations should be sumciently close (in the sense of 840 described in ~igure 8) to references of target object in database.
Instep 260 of the algorithm 200, normalizcd characteristics of the target object 131 are compared 260 to one or morc normalized reference object ch~racteristics. This comparison 260 depends very much on the method for characterizing object features, for which examples are given in step 240 above. One preferred comparison 260 is done with of area or length normalized histograms.
15 One or more reference object characteristics are stored 270 on a memory storage device. This device can be located in memory on the computer 140 or a separate secondary storage device 144. A preferred method for storing 270 the reference object characteristics is to use a series of area normalized feature histograms that characterized object features. Each of these series of area normalized histograms has associated with it a unique object type identifier. A preferred method 20 of storing the area normalized feature histograms is by using a vector of normalized feature histograms. That is, the normalizecl frequcncies of occurrencc of the different feature values.
Figure 6 is a flow chart showing one preferred mcthod nr devcloping a histogram of a feature.
In this non-limiting example, the feature, Fl, Hue is used. However, any feature that can be 25 extracted from the segmented image can be used. Note that thc present invention novelly extracts the feature only from the segmented object image(s) 130. The feature histogrammed also can be derived from other information about thc segmcnted object. For example, Hue could be derived from some other feature in a colour map.
214~404 -To develop the histogram 650, the scene is first imaged (step 210 of Figure 2) and the object image 130 is segmented 220. The feature to be histogrammed is then computed or determined using prior art techniques 230, preferably on a pixel by pixel basis (but could also be done for every other pixel, or any pre-determined subset of pixels) Prior art techniques are then used to develop 640 the histogram 650 of the feature, Fl.
For example, a histogram array of M intervals (bins) is first initialized to zero. Then, on a pixel by pixel basis, the Hue of pixel is computed. This computed Hue value for a particular pixel is quantized so that it will fall into one of the M bins, say Bin(x), of the histogram. The content of Bin(x) is then incremented by one, i.e., New Bin(x) = Old Bin(x) + 1. This is done for all pixels in segmented object image 130, or for sclected subsets (e.g., every other one) of these pixels.
The Hue histogram 650 is a representation of how colour (Hue) is distributed in the image of segmented object(s) 130. In other words, the content of each bin describes how many pixels in 130 have colour represented by that bin. lf Ft is somc other feature, it is a representation of how that feature is distributed in image of object 130. The content of each bin describes how many pixels in 130 have feature value reprcsented by that bin.
Figure 7 is a flow chart showing the stcps of normalizing a histoglam feature and how these normalized feature histograms are unaffecte<l by the size or number of the object(s) 131 imaged.
Image 320 is a segmented colour imagc exhihiting onc segmentcd object 131 image 130. Image 720 is a segmented colour image of thrcc instanccs of object 131, exhibiting three segmented object images 130. One or more featurc(s) Fl arc computed as described in Figure 6, and two histograms are developed, histogram 745 and histogram 740, respectively. In step 750, each histogram (745, 740) is normalizcd using thc same method of normalization 750. Since the present invention novelly normalizes 750 only thc segmentcd images of the objects (130) in each image (320, 720), the resulting normalized histogram (770 and 760 respectively) are identical.
This result occurs even though the imagc 720 with a larger numbcr of objects 131 will contribute ~- 21~4~04 a higher pixel count to each bin of the histogram 740 than the image 320 with a fewer number of objects 131 will contribute to its respective histogram 745. (Note that the same effect occurs if the size of the object 131 is greater 720 in one image than in the other 320.) For example, area normalizing creates approximately equal normalized histograms (760, 770) because the S contribution of the segmented image to its histogram is divided by its respective image area.
Areal, that is the segmented object image area 130 in colour image 320 is computed by adding the content of all the bins of histogram 745. Area2, that is the segmented area for all the objects 130 (or the larger sized object3 for image 720 is computed in same fashion. To obtain area normalized histogram 760, histogram 745 is divided, bin by bin, by the value Areal. The area normalized histogram 770 is computed by dividing bin by bin histogram 740 by Area2. After this operation, area normalized histogram 760 is approximately cqual to area normalized histogram 770 and readily compared 260 as in the description of Figure 8.
Normalization can be done with respect to any property that can be extracted from segmented object image 130. Area, length, and size are examples. Other measures that describe the shape can be used, such measures include but are not limited to, second and higher-order (shape) moments, the size of bounding rectangle, area of the convex hull of object image 130.
Figure 8 illustrates the step 260 of algorithm 200 that compares 840 the normalized characterizations (760, 770) of the segmented target image t 30 to one or more stored normalized reference characterizations 270. Characterization 810 represents normalized characterization of some segmented image containing a targct object. This characterization is obtained as described in Figure 7. Block 820 is a list (databasc) of arca normalized rcfercnce characterizations obtained as described, e.g., in Figure 9. These are representations of the objects that the system is to be able to recognize. Each of the plurality of normalized characterization representations are labelled typically as 831, ..., 837. Only six arc shown, but the number of area normalized histogram representations can be very large, e.g., in the 100s or cven 1000s. Each object to be recognized should be represented by at Icast one normalized characterization but can be -represented by more than one normalized characterization. Each area normalized characterization in 820 has associated with it a descriptive identifier of the object that the normalized characterization is developed from. Characterization 810 and reference characterizations 820 are not limited to one characterization, representation can be multiple 5 characterizations. In that case, multiple characterizations are developed from the image of the target object while multiple characterizations represent each reference object. Again, each such collection of characterizations is associated with a unique object identifier. See the description of Figure 10.
10 Block 840 shows the comparison/matching of the target characterization to the reference characterizations. A preferred means of matching/comparing characterizations is to determine a distance measure, Ll, between target histogram and reference histograms. For example, let target histogram 810 be represented as a vector T of numbers and reference histograms 820 as vectors Rl through some RN. For this disclosure, the best match of the target histogram T is 15 defined as that reference histogram Rl for which the Ll distance (sometimes called Manhattan distance) between T and Rl ... Rl ... RN is smallest. That is, Rl would give the smallest Ll distance of distances .Si Dist (T-RJ), ..., .1= 1,2, ...., N
Matching algorithms like this are well known as nearest neighbour classification. Any measure 20 of distance that exhibits the usual properties of a distance measure can be used here. Further, other measures that do not exhibit properties of distance, e.g., Histogram Intersection, could be used. Weights can be associated with the components of target histogram T and reference histograms Rl ... RN, resulting in a component-wise weighted distance measure.
25 If target object and reference objects are represented by multiple histograms, preferred representations can be viewed as higher dimensional vectors containing multiple concatenated histograms, T' and Rl' ... RN'. One preferred way to define the best match of such a concatenated target histogram to T' is defined as that concatenated reference histogram Rl' for which the Ll distance between T' and Rl ... RN' is smallest. Here, different weights may be 214~04 assigned to different subvectors, representing different feature histograms, in the Ll distance.
Again, any distance measure can be used, and also measures that do not exhibit properties of distance, e.g., Histogram Intersection, can be applied. Weights can be associated with every with the components of target histogram T' and reference histograms R1' ... RN', resulting in a component-wise weighted distance measure.
It is intended in this invention that objcct(s) 131 shown is of one type. Presenting multiple objects, Object A and Object B, can result in unprcdictable results. The most likely result is that objects are flagged as unrecognizablc. It could happen howevcr, due to the distance measure used, that recognition result is: (1) object is Object A; (2) object is Object B; (3) object is Object A or Object B - presented as choices in user interface of Figure 5. The latter happens when mixed objects are of similar appearancc, likc, Granny Smith apples and Golden Delicious apples.
It is unlikely that objects are rccognized as some othcr Object C stored in 820.
Figure 9 is a flow chart showing the method 910 steps for training the system by adding to storage 270 (concatenated) reference histograms that meet certain storage criteria 255. The training method 910 enables the apparatus 100 to recognize new objects/items, i.e., those not originally stored in the system storage 270. The training 910 be~ins by presenting the apparatus with an image 920 of the objectlitem. The image is segmcnted 220 and then features are determined 230 for histogramming G40 as described above. The normalized (concatenated) histogram 750 is compared 260 as beforc. If the target normalizcd histogram is matched with a reference normalized histogram in storagc, the targct image is rccognized. If not, the method 910 continues to check the target normalizcd imagc against certain storagc criteria 255. If the storage criteria are not met, the method ends 94(). 940 not in drawing. RMB 4/26 If the target normalized image meets the storage criteria 255, thc target normalized image is stored in the storage device 270 where it can be used later to match other target images.
It is important that image 920 is obtained with device operating in same fashion as will be used later on recognize different instances of sakl object(s) l 31. The preferred embodiment of such a 214441)4 -device is described in Figure 4 with and polarized light through filter 410 and polarizing filter 420 on camera. Polarization is of particular importance because during training and recognition, object(s) 131 can have very unpredictable specular reflection (glare) effects.
5 Training also can be achieved through interactive input/output device 160; it can be achieved through human intervention, either by cashier in front end or by produce manager in back room.
This is further described in Figure 15.
Figure 10 is a flow chart showing the steps of extracting more than one feature from an image 10 and using more than one feature to identify an object. The method begins with an image 320 of an object 130 and background 311. As before, the object image 130 is segmented 220 from the background 311. Multiple features are then extracted from segmented image 320 in the same manner as Hue Fl (230) is extracted as described above. Blocks 1010 ... 1020 typically refer to other plurality of features extracted. These include, but are not limited to, Saturation, Intensity, IS Texture (described in Figure 11), Boundary Shape (described in Figure 12) and Density (described in Figure 13). As for colour, the HSI representation is the preferred means of representing colour for this invention. Other colour representations may be used, including, but not limited to RGB, Munsell, opponent colours.
20 Vnce the features Fl - FN are extracted, they are histogrammed and normalized as described above. Although many features, like colour can be area normalized, other normalizations (e.g., length, boundaries) are possible that might be particularly suited to a feature. For example, see below in Figure 12 for shape histograms.
25 In step 840, each of the extracted features, Fl - FN, are compared. This comparison is already described in Figure 8. Essentially the extracted N histograms (of features Fl - FN) are concatenated in a long histogram and comparison is based on some distance measure between target concatenated histogram and reference concatenated histograms. In this distance measure, histograms of individual features Fl - FN could be weighted with different weights wl - wN.
214~4~4 -Alternatively, in distance measure, each individual component of concatenated histogram can have a individual weight. As mentioned above, features Fl - FN include, but are not limited, Hue, Saturation, Intensity, Texture, Shape. Not all of these features have equal discriminative power, and therefore, weights wl - wN may be used. Moreover, not every component of an individual feature, say FI, may have equal discriminative power. So, individual feature histograms can be weighted differently component-wise.
Figure 11 illustrates how texture is used as a normalized recognition feature. Block 210 is an image of an object/item that exhibits the feature of texture 1120. As before, the object image is segmented 220 from its background. In step 1140 the texture feature is computed from the segmented image. Any texture measure known in the prior art could be used in this 1140 computation. However, two novel computation are preferred.
The first preferred means of texture computation is a novel texture measure A:
Segmented image is transferred into a binary image by selecting a threshold Tb using methods in the prior art. If image brightness is larger than Tb, binary image is set to l;
if image brightness is smaller than Tb, binary image is set to 0. Other means, known to a person skilled in the art, for binarizing images also can be used. The result is a blob-like black and white image. Each blob can be characterized by a Width and a Length; the texture measure (WE) associated with a blob is given by Width Eccentricity = Width/Length This is a texture measure which is determined using re~ion calculations.
A second preferred novel texture measure B is the following.
The image is convolved using prior art methods with [-1 2 -1] mask, this convolution is 21~404 -performed both vertically and horizontally, denoted by Vconv and Hconv, respectively.
At each pixel x where the convolution result is over some threshold T2, the vector consisting of Magnitude and Direction Magnitude = sqrt ( Vconv(x)**2 * Hconv(x)**2) Direction = arctan ( Vconv(x)/Hconv(x) ) are defined as the texture measure. This is a texture measure which is determined using ed~e calculations.
The texture feature can also be histogrammed ;n a novel way 1150, that is, only over segmented object image 1120. The texture measures are histogrammed over the segmented image as described above. For texture measure A, this results in (Width-Eccentricity) histogram, where Width and Eccentricity are defined above. Texture measure B, gives a (Magnitude-Direction) histogram, where Magnitude and Direction are defined above. For the Direction histogram, the maximum direction in the Direction histogram is computed and the histogram cyclically shifted to bring this peak to the centre. This will make the Direction histogram independent of the rotation under which texture is imaged.
Texture histograms are normalized by count. Here count can be each pixel in segmented object image 1120, or count could be those pixels in segmented object image 1120 that actually exhibits texture. Other shape measures cxtracted from the textured region can be envisioned by a person skilled in the art. A resulting normalizcd tcxturc histogram is shown as 1170. Use of texture histograms for recognizing objccts is bclievc(l novcl.
Figure 12 is a flow chart showing the steps of using shape as a recognition feature. The image 210 is segmented 220 as above. Next a determination of which pixels in object image 130 are boundary pixels is made 1210. A pixel P is a boundary pixel if one or more neighbouring pixels of P belong to background image 311. Next a determination is made of a boundary shape 2144~04 property 1220 for each boundary pixel P. A preferred shape measure used by this invention is local boundary curvature at pixel P. The radius R of a circle that fits the centre pixel P and number of the surrounding boundary pixels is first computed by computer 140. The curvature l/R describes the local degree of variation for pixel P - zero curvature for a straight line 5 boundary, high curvature for a locally "wiggly" boundary. An apple will have a roughly constant curvature boundary, while a cucumber has a piece of low curvature, a piece of low negative curvature, and two pieces of high curvature (the end points). Other shape measures are possible.
10 The boundary shape feature(s) are then histogrammcd 1230 The histogramming is developed by the computed shape properties of boundary pixels P. Instead of over an area, histograms here are developed from a collection of imagc pixels P that comprisc the boundary of object image 130.
15 The normalization done 1235 is a length normalization of the shape histogram. Bin by bin, the histogram of 1230 is divided by the total number of boundary pixels P. The result is that the length normalized shape histogram of one object image 130 is equal to the length normalized shape histogram of multiple object imagcs 130. Length normalized object image boundary shape histograms are a novel feature of this invcntion. Othcr normalizations related to length of the 20 object image boundary are possible.
Density can be an important recognition fcature. A pound of white onions weighs as much as a pound of mushrooms, but the volumc of thc mushrooms is much larger than that of the white onions. Therefore, the relation bctwcen wcight and volume is important. This relation is object 25 density determined by Density = Weight (Object 131) / Volume (Objcct 131) Figure 13 is a block diagram showing the computer 140 connected to a weighing device 170 that 21444~)4 -determines the weight of the objcct(s) 131. To use weight as recognition feature, device 170 reports the weight of object(s) 131 to computing device 140. In a preferred embodiment, the system 100 uses a weight a "Density" feature defined as "Density" = Weight (Object 130) 1 Area (Segmented object 131) This measure does not embody the conventional means of referring to density, rather it is a measure of pressure. It is called the avera~e projccted density.
True density of object(s) 131 can only be computed very roughly. To get an idea of the volume of object(s) 131, the boundary contour(s) of 130 can be approximated with an ellipse and the volume(s) of 131 can be approximated by the volume of an ellipsoid of revolution developed from the approximated ellipse. Density, then, is given by Weight/Volume.
Other means for estimating volume from a projected segmented object image 130 are within the scope of this invention.
Multiple reference histograms representing the same feature Fl (e.g., Hue) can be used to recognize a given object. Figure 14 shows an image 14()5 where segmented object image 130 has two distinct regions, i.e., the leaves 1410 and the grapes 1420. The image 1405 comprises the object 130 and background 311. The object image 13() is segmcnted along with its first object region 1410 and its second 1420 object region. These object regions are recognized and defined by using a segmentation algorithm. A prcfcrred algorithm is the use of an area normalized Hue histogram for detecting if there are two or more distinct peaks.
These regions are histogrammed and arca normalizcd separately. Area normalized histograms 1450 and 1455 correspond to the first 1410 and second 142() region, respectively, and are compared to reference histograms as described abovc. Additionally, relative location 1430 of regions 1410 and 1420 can be taken into account during matching (Figure 8). This part of the invention accounts for items where a fcature, e.g., colour, but not limited to colour, is not 2144~4 uniform over the surface of the object 131 and hence not uniform over the segmented object image 130. A typical example are carrots with the leafy part left on.
Figure 15 shows an optional human interface 160. It comprises a preferred means of displaying 164 of pictorial (or otherwise explained) description(s) 1510, 1520, 1530 and 1540 of various possible identities of object(s) 131 that are determined by apparatus 100. In most cases, object(s) 131 can be uniquely identified by comparison 260 to the reference database 270. However, in some case, there may be a match to more than one reference histogram, i.e., the target object normalized histogram may be approximately the same as more than one reference histogram. In these cases a human can be novelly asked through the interface 160 to make the final recognition decision. A preferred embodiment of the interface 160 offers four or fewer choices - 1510, 1520, 1530, 1540. More choices can be optionally requested as explained later. The human can communicate the decision to computer 140 through any means, touch, voice, mouse, keyboard.
In addition, a means (button) 162 can be provided on the interface to enable the user to determine when and if a histogram should be added to the reference object database 820 in storage 270, i.e., if the system is to be trained with that data to recognize (or better recognize) instance of object 131 when presented to system 10() at some future point.
Figure 16 shows an interface 160 with a function, like a browsing key, that allows the user to browse for an obJect identity. A browsing key refers to a key word or key feature by which to narrow down the human guided search for object identity in the database g20. Examples of such keys are, but are not limited to: Red 1612, Green 1613, Yellow 1614, Brown 1615, Round 1616, Straight 1617, Leafy 1618, Apples 1619, Cilrus Fruits 1620, Peppers 1621, and Potatoes 1622, as displayed in 1610. The user can communicate through touch, voice, mouse, keyboard, etc. The key 1600 will respond with either another instance of 1610, in which the choices presented 1612 - 1622 are more specific, or with screen 1630 where a final deci~sion can be made. If 1619, e.g.
apples, is selected, 1600 will present human with screen 1630, offering descriptions (sketches, photographs, words) 1631 - 1641 of identity of the object(s) 131. The user can select choices on the screens using various known input devices. Any other human-friendly method or means can 2144~04 `
Figure 17 is a block diagram showing optional apparatus used with system 100 to price objects.
A weighing device 170 is used to determine the weight of object(s) 131. The apparatus 100 5 recognizes the object as described above. Once the object is recognized, a price of the object is determined. The weight 170 and or the count (number of items present) of the objeet is used if required in the prieing. The prices of the objects are stored in memory 144.
Priee device 1710 is attached to apparatus 10() to communicate the price to the user. Price device 10 1710 ean be a printing deviee, display device, or any other means of communieating the price of the object. The price ean also be displayed on the interactive output device lG0.
If price is speeified by pound, the eomputer 140 ealeulates price as Price = Weight * (Price of object 131 per pound) If price is specified by count, computer 140 ealeulates priee as Priee = Count * (Unit priee of objeet 131) Item eount ean either be obtained through human intervention or can be estimated.
For entering count through human intervention, system 100 will simply prompt human to enter count if item 131 is indicated in eomputer memory 140 as being sold by eount (e.g., lemons, limes). There are two ways automatically estimating Count:
a) Apparatus 100 has average weight of object 131 in memory 144 and Count is eomputed as Count = Weight / Average weight (object 131) after identity of objeet 131 is established from segmented objeet image 13.
-b) Apparatus 100 makes an estimate of number of segmented object images 130 are present, and Count = Number of segmented object images 130.
a. a light source for illuminating one or more of the objects, the illuminated objects being a target object, the light source having a non-monochromatic light frequency distribution that is constant over a period of time;
b. a computer system having a visual input device for creating one or more scene images, the scene images capable of including a target object image of the target object and a background image, and the computer system further having a memory storage;
c. a segmenter executing on the computer system that produces a segmented target object image by segmenting the target object image from background image by comparing a first scene image with a second scene image, the first and second scene images being in spatial registration and one or more respective positions in the first and second scene images having a difference being identified as the target object image;
d. a plurality of reference normalized characterizations, each reference normalized characterization being of a feature associated with a segmented reference object, the reference normalized characterizations being stored in the computer memory storage; and e. a normalizer executing on the computer system that produces one or more target normalized characterizations, each target normalized characterization being of a feature of the segmented target object image, whereby one or more of the target normalized characterizations, is compared with one or more reference normalized characterizations and the target object is recognized as the associated reference object if the compared target normalized characterizations and reference normalized characterizations match.
a. a light source for illuminating a scene, the light source having a non-monochromatic light frequency distribution that is constant over a period of time, the light source controlled to illuminate the scene at a first illumination level and at a second illumination level lower than the first illumination level, the scene comprising one or more of the objects, being a target object, and a background;
b. a computer system having a memory storage, a visual input device for creating a scene image including a target object image of the target object and a background image, and an algorithm that produces a segmented target object image by segmenting the target object image from the background image in the scene image, the algorithm segmenting the target object image by comparing a first scene image taken at the first illumination level with a second scene image taken at a second illumination level;
c. a plurality of reference normalized histograms, each of the reference normalized histograms being a histogram of a feature associated with an associated segmented reference object, the reference normalized histograms being stored in the computer memory storage; and d. a normalizer that produces one or more target normalized histograms, each of the target normalized histograms being a histogram of a feature of the segmented target object image, the normalizer normalizing each of the target normalized histograms the same way as the reference normalized histograms are normalized, whereby one or more of the target normalized histograms, is compared with one or more of the reference normalized histograms and the target object is recognized as the associated segmented reference object if the target and reference normalized histograms of a feature match.
a. a scale that weighs the target object;
b. a reference segmented object average projected density of the object, a representation of the reference projected density being stored in computer memory storage; and c. a target segmented object projected density;
whereby the target object projected density must match the reference projected density in order to identify the target object.
a. a light source for illuminating a scene, the light source having a non-monochromatic light frequency distribution that is constant over a period of time, the light source controlled to illuminate the scene at a first illumination level and at a second illumination level lower than the first illumination level, the scene comprising one or more of the objects, being a target object, and a background;
b. a computer system having a memory storage, a visual input device for creating a scene image including a target object image and a background image, and an algorithm that produces a segmented target object image by segmenting the target object image from the background image in the scene image, the algorithm segmenting the target object image by comparing a first scene image taken at the first illumination level with a second scene image taken at the second illumination level;
c. a plurality of reference normalized histograms, each reference normalized histogram being a histogram of a feature associated with a segmented reference object, the reference normalized histograms being stored in the computer memory storage; and d. a normalizer that produces one or more target normalized histograms, each of the target normalized histograms being a histogram of a feature of the segmented target object image, the normalizer normalizing the target normalized histograms the same way as the reference normalized histograms are normalized; and e. a means for determining if an unrecognized target object image meets a set of storage criteria, whereby one or more of the target normalized histograms is compared with one or more of the reference normalized histograms and the target object is not recognized as the associated segmented reference object because the target and reference histograms of a feature do not match and the target normalized histogram is stored in memory storage if it meets the set of storage criteria.
a scale that weighs the object,~
whereby the price of the bulk item is determined based on the weight and recognition of the object.
a. illuminating one or more of the objects, the illuminated objects being a target object, with a light source, the light source having a non-monochromatic light frequency distribution that is constant over a period of time;
b. creating a scene image with a computer system having a visual input device, the scene image comprising a target object image and a background image, the computer system having a memory storage an algorithm for producing a segmented target object image by segmenting the target object image from the background image of the scene;
c. producing one or more target normalized characterizations, each target normalized characterization being a characterization of a feature of the segmented target object image;
d. comparing one or more of the target normalized characterizations to one or more reference normalized characterization in memory storage, each reference characterization of a feature associated with a segmented reference object; and e. recognizing the target object as a reference object when one or more or the target normalized characterizations matches one or more of the reference normalized characterizations.
Priority Applications (2)
|Application Number||Priority Date||Filing Date||Title|
|US08/235,834 US5546475A (en)||1994-04-29||1994-04-29||Produce recognition system|
|Publication Number||Publication Date|
|CA2144404A1 CA2144404A1 (en)||1995-10-30|
|CA2144404C true CA2144404C (en)||2002-04-16|
Family Applications (1)
|Application Number||Title||Priority Date||Filing Date|
|CA 2144404 Expired - Fee Related CA2144404C (en)||1994-04-29||1995-03-10||Produce recognition system|
Country Status (10)
|US (1)||US5546475A (en)|
|EP (1)||EP0685814B1 (en)|
|JP (1)||JP3369772B2 (en)|
|KR (1)||KR100190737B1 (en)|
|CN (1)||CN1092375C (en)|
|AT (1)||AT196695T (en)|
|AU (1)||AU685904B2 (en)|
|CA (1)||CA2144404C (en)|
|DE (2)||DE69518947D1 (en)|
|ES (1)||ES2151000T3 (en)|
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