TWI604411B - Structured-light-based exposure control method and exposure control apparatus - Google Patents

Description

Structure light-based exposure control method and exposure control device

The present invention relates to an exposure control method and an exposure control device, and more particularly to an exposure control method based on structured light and an exposure control device.

In the field of computer graphics, the geometric measurement technology for the appearance contour of objects has three-dimensional image acquisition and data analysis in industrial applications, reverse engineering, manufacturing parts inspection, digital cultural relics collection, cultural relics archaeology, etc. Demand.

In the case of existing time-coded structured light, it provides fairly fine stereoscopic scan results. The scanning method is to use the structured light with different phase shifts and frequencies to project onto the surface of the object, and then use the image capturing device to capture multiple images of the structured light deformed by the surface contour of the object to obtain the object by image analysis. Complete surface information. However, when projecting a pattern having structured light to the surface of the object, stereoscopic information may be calculated due to excessive stereoscopic information caused by overexposure or low confidence due to insufficient exposure.

The invention provides an exposure control method based on structured light and an exposure control device for controlling exposure conditions to improve image quality of stereoscopic scanning.

The structured light-based exposure control method of the present invention is applicable to an exposure control device having a projector and an image capturing device, and the exposure control method includes: performing a structured light scanning operation on an object according to a plurality of exposure conditions to generate a corresponding plurality of images The optimal exposure condition is determined from the exposure conditions, wherein the exposure failure value of the image group corresponding to the optimal exposure condition is smaller than the exposure failure value of the other image group, and the exposure failure value is obtained by each image group The number of overexposed pixels and the degree of confidence are determined by the number of low pixels; and the stereo image of the object is calculated according to the image group corresponding to the optimal exposure condition.

The structured light-based exposure control apparatus of the present invention includes a projector, an image capture device, and a processor. The processor is coupled to the projector and the image capturing device. The processor instructs the projector and the image capturing device to perform a structured light scanning operation on the object according to the plurality of exposure conditions to generate a corresponding plurality of image groups. The processor determines an optimal exposure condition from the exposure conditions. The exposure failure value of the image group corresponding to the optimal exposure condition is smaller than the exposure failure value of the other image group. The exposure failure value is determined by the number of overexposed pixels in each image group and the number of low confidence pixels. The processor calculates a stereoscopic image of the object according to the image group corresponding to the optimal exposure condition.

Based on the above, the exposure control method and the exposure control device of the present invention determine an optimal exposure condition from a plurality of exposure conditions, and calculate a stereoscopic image of the object based on the image group corresponding to the optimal exposure condition.

The above described features and advantages of the invention will be apparent from the following description.

The components of the present invention will be described in detail in the following description in conjunction with the accompanying drawings. These examples are only a part of the invention and do not disclose all of the embodiments of the invention. Rather, these embodiments are merely examples of the methods and apparatus in the scope of the patent application of the present invention.

1 is a block diagram of an exposure control apparatus according to an embodiment of the invention. 2 is a schematic diagram of an exposure control apparatus according to an embodiment of the invention. However, this is for convenience of description and is not intended to limit the invention.

Referring to FIGS. 1 and 2 , the exposure control device 100 includes a projector 110 , an image capturing device 120 , and a processor 130 . The processor 130 is coupled to the projector 110 and the image capturing device 120. The exposure control device 100 can scan the object T to obtain stereoscopic information of the object T. In this embodiment, the image capturing device 120 can be disposed above the projector 110, as shown in FIG. However, the present invention is not limited to the arrangement in Fig. 2. For example, projector 110 and image capture device 120 can be horizontally disposed or otherwise disposed from each other.

In this embodiment, the image capturing device 120 is configured to capture an image of the object T. The image capturing device 120 includes a lens and a photosensitive element. The lens is composed of a lens, and the photosensitive element is used to respectively sense the intensity of the light entering the lens, thereby generating an image separately. The photosensitive element may be, for example, a charge coupled device (CCD), a complementary metal-oxide semiconductor (CMOS) element, or other elements, and the invention is not limited thereto.

In this embodiment, the processor 130 is coupled to the projector 110 and the image capturing device 120. The processor 130 can be, for example, a central processing unit (CPU), or other programmable general purpose or special purpose microprocessor, digital signal processor (DSP), Programmable controllers, Application Specific Integrated Circuits (ASICs), programmable logic devices (PLDs), or other similar devices or combinations of these devices.

It should be understood by those skilled in the art that the exposure control device 100 further includes a data storage device (not shown) that can be coupled to the projector 110, the image capturing device 120, and the processor 130 for storing images and data. The data storage device may be, for example, any type of fixed or removable random access memory (RAM), read-only memory (ROM), flash memory, or flash memory. A hard disk or other similar device or a combination of these devices.

In this embodiment, the processor 130 may instruct the projector 110 to perform a structured light scanning operation on the object T, that is, instruct the projector 110 to sequentially project a structure light having a plurality of scanning patterns on the object T to scan the object T. For example, the projector 110 can sequentially project the structured light having the scanning patterns 1-6 to the object T. The scan patterns 1-3 may have a first spatial frequency and the scan patterns 4-6 may have a second spatial frequency different from the first spatial frequency. Scan Patterns 1-3 and Scan Patterns 4-6 can be sinusoidal or cosine wave patterns, and each can have three different phase shifts (eg, -120 degrees, 0 degrees, and 120 degrees). When the structured light having the scanning pattern 1-6 is projected on the object T, the processor 130 instructs the image capturing device 120 to capture a plurality of images of the object T. Therefore, the three different phase shifts of the scan pattern 1-3 and the scan pattern 4-6 can respectively correspond to one of the plurality of images captured by the image capture device 120, more precisely, when having the scan pattern 1 When the structured light is projected on the object T, the image capturing device 120 captures the image corresponding to the scanning pattern 1 of the object T, and so on when the structured light having other scanning patterns is projected on the object T. It should be noted that although in the present embodiment, the object T is scanned by the structured light of two sets of scanning patterns of different spatial frequencies, the present invention is not limited thereto. In another embodiment, the structured light of the scanning pattern of three or more sets of different spatial frequencies may also be scanned to achieve a more accurate scanning effect. Further, although the scanning pattern at the same spatial frequency in the present embodiment has three different phase shifts, the present invention is not limited thereto. In another embodiment, the scan pattern at the same spatial frequency may also have four or other different phase shifts.

FIG. 3 is a flow chart of an exposure control method according to an embodiment of the invention.

In step S301, a structured light scanning operation is performed on the object T according to a plurality of exposure conditions to generate a corresponding plurality of image groups. The exposure conditions may be the brightness of the projector 110, the aperture size of the image capturing device 120, the synchronized exposure time of the projector 110 and the image capturing device 120, or the range of varying intensity of the scanned pattern (eg, an exposure value of 0-255). Scan the pattern or scan pattern with an exposure value of 0-127). Taking the exposure condition as the brightness of the projector 110 as an example, the processor 130 can instruct the projector 110 to project the structured light having the scanning pattern 1-6 at different brightnesses on the object T, so that the image is projected at each projector 110. The capture device 120 can extract an image group (for example, images 1-6 corresponding to scan patterns 1-6).

In step S303, an optimum exposure condition is determined from the above exposure conditions. The exposure failure value of the image group corresponding to the optimal exposure condition is smaller than the exposure failure value of the other image group. The exposure failure value is determined by the number of overexposed pixels in each image group and the number of low confidence pixels.

Specifically, the processor 130 calculates an overexposed map for each image group and marks overexposed blocks in the overexposed map. Taking FIG. 4 as an example, when the processor 130 is calculating the overexposed map 400 of an image group, the processor 130 may find the overexposed block 410 according to the preset exposure threshold. In detail, when the exposure value of a pixel in any of the images in the image group is greater than the exposure threshold, the processor 130 determines that the pixel is an overexposed pixel and marks the pixel in overexposure. In block 410. Taking the octet exposure value as an example, the exposure threshold can be set to 250. The overexposed map 400 can be implemented using the following equation:

Overexposed map = (Image 1 > Exposure threshold) *...* (Image n > Exposure threshold). Image 1 to image n represent the exposure values of all pixels from image 1 to image n.

In the above equation, n is a multiple of the number of scan patterns of the same spatial frequency. For example, in the present embodiment, n may be 3 or 6.

That is, the processor 130 can determine whether each pixel in the image group is overexposed by the above equation and calculate the overexposed map 400 including the overexposed block 410.

In addition, the processor 130 also calculates a map of insufficient confidence for each image group and marks an insufficient confidence block in the map with insufficient confidence. Taking FIG. 5 as an example, when the processor 130 is calculating the confidence level of the image group less than the map 500, the processor 130 may find the lack of confidence block 510 according to the preset confidence threshold value. In detail, when the confidence of a pixel in an image group is less than the confidence threshold, the pixel is judged to be too low in confidence and the pixel is marked in the low confidence block 510. , where confidence is the degree of change in the exposure value of the pixel in this image group. Insufficient confidence map 500 can be implemented using the following equation:

Insufficient confidence map = (I ² + Q ² ) ^1/2 , where I = (2 * image 2 - image 1 - image 3), Q = tan (120 / 360 * π) * (image 1 - image 3) . The image 1-3 represents the exposure value of all pixels of the image 1-3.

In detail, the exposure values of the pixels in the images 1-3 can be expressed by the following equations (1), (2), (3):

………(1)

………(2)

.........(3)

In equations (1)-(3), , , The intensity of the exposure value of the pixels in the image 1-3, For the corresponding ambient light intensity Corresponding to the brightness of the structure projected by the projector, For the phase angle, For phase shift. In this embodiment, It is 120 degrees.

.........(4)

In equation (4), the phase angle is eliminated by the operation of the left half of the equal sign. Corresponding to ambient light intensity And the corresponding value of the structural lightness projected by the projector Dependence and get the phase angle versus , , Phase shift The relationship is shown in equation (5), and finally equation (6) is derived from equation (5).

).........(5)

.........(6)

In this way, the confidence is not enough for the map I is And Q is And the above confidence can be regarded as the length of the triangle bevel, as shown in Figure 6.

It can be seen from the above equation that the lower the degree of change of a pixel in an image group, the lower the calculated confidence. When the confidence of a pixel in an image group is less than the confidence threshold (eg, 10), the processor 130 marks the pixel in the confidence low block 510.

After the processor 130 calculates the overexposed block 410 and the lack of confidence block 510, the number of overexposed pixels and the low confidence can be obtained from the overexposed block 410 and the lack of confidence block 510. The number of pixels. In the present embodiment, the processor 130 may set the exposure failure value to the sum of the number of overexposed pixels and the number of low confidence pixels. However, the invention is not limited thereto. In another embodiment, the processor 130 may set the exposure failure value to the number of overexposed pixels multiplied by the first weight parameter and the number of confidence low pixels multiplied by the total of the second weight parameters. .

Next, the processor 130 may calculate an exposure failure value corresponding to each exposure condition, and set an exposure condition having a minimum exposure failure value as an optimum exposure condition, as shown in FIG.

In step S305, a stereoscopic image of the object is calculated according to the image group corresponding to the optimal exposure condition.

It should be noted that the area in which the exposure failure value is calculated in this embodiment is the entire picture of the image, but the invention is not limited thereto. In another embodiment, the exposure failure value may also be calculated only for the Region of Interest (ROI) to reduce the computation time.

In summary, the exposure control method and the exposure control apparatus of the present invention can calculate the initial correspondence each according to the number of overexposed pixels in the image group corresponding to each exposure condition and the number of low pixels of confidence. The exposure condition is unqualified, and the optimal exposure conditions with the smallest exposure failure value are found from a plurality of exposure conditions, and the image group corresponding to the optimal exposure condition is used to generate a stereoscopic image to effectively improve the accuracy of the stereoscopic scanning.

Although the present invention has been disclosed in the above embodiments, it is not intended to limit the present invention, and any one of ordinary skill in the art can make some changes and refinements without departing from the spirit and scope of the present invention. The scope of the invention is defined by the scope of the appended claims.

100‧‧‧Exposure control device
110‧‧‧Projector
120‧‧‧Image capture device
130‧‧‧Processor
T‧‧‧ objects
Steps of S301, S303, S305‧‧‧ exposure control method
400‧‧‧Overexposed map
410‧‧‧Excessively exposed blocks
500‧‧‧Insufficient confidence map
510‧‧‧Insufficient confidence block

1 is a block diagram of an exposure control apparatus according to an embodiment of the invention. 2 is a schematic diagram of an exposure control apparatus according to an embodiment of the invention. FIG. 3 is a flow chart of an exposure control method according to an embodiment of the invention. 4 is a schematic diagram of an overexposed map according to an embodiment of the invention. FIG. 5 is a schematic diagram of a map of insufficient confidence according to an embodiment of the invention. FIG. 6 is a schematic diagram showing the relationship between phase angle and confidence according to an embodiment of the invention. FIG. 7 is a schematic diagram showing the relationship between exposure conditions and exposure failure values according to an embodiment of the invention.

Steps of S301, S303, S305‧‧‧ exposure control method

Claims (14)

An exposure control method based on structured light is applicable to an exposure control device having a projector and an image capture device, the exposure control method comprising: performing a structured light scanning operation on an object according to a plurality of exposure conditions to generate a corresponding a plurality of image groups; determining an optimal exposure condition from the exposure conditions, wherein an exposure failure value of the image group corresponding to the optimal exposure condition is smaller than the exposure failure value of the other image groups, the exposure The unqualified value is determined by the number of overexposed pixels in each of the image groups and the number of pixels that are too low in confidence; and calculating the object according to the image group corresponding to the optimal exposure condition A three-dimensional image. The exposure control method of claim 1, wherein the structured light scanning operation comprises: sequentially projecting a structure light having a plurality of scan patterns on the object to scan the object; and having the When the structured light of the scanned pattern is projected on the object, the image capturing device is used to capture a plurality of images of the object. The exposure control method of claim 2, wherein when a pixel has an exposure value greater than an exposure threshold in any of the image groups, determining the pixel is Overexposed pixels. The exposure control method of claim 2, wherein when a pixel has a confidence level in each of the image groups less than a confidence threshold, determining that the pixel is too low in confidence. A pixel, wherein the confidence is a degree of change of an exposure value of the pixel in each of the image groups. The exposure control method of claim 2, wherein the exposure conditions are brightness of the projector, aperture of the image capturing device, exposure time of the projector and the image capturing device, or the scanning The intensity of the change in the pattern. The exposure control method of claim 2, wherein the scan patterns comprise a first spatial frequency and a specific pattern of a second spatial frequency. The exposure control method of claim 2, wherein the structured light of each of the scan patterns has at least three different phase shifts, and each of the phase shifts respectively corresponds to one of the images. An exposure control device based on structured light, comprising: a projector; an image capture device; and a processor coupled to the projector and the image capture device, wherein the processor indicates the projector and the image The taking device performs a structured light scanning operation on an object according to a plurality of exposure conditions to generate a corresponding plurality of image groups, wherein the processor determines an optimal exposure condition from the exposure conditions, wherein the optimal exposure condition corresponds to The exposure failure value of the image group is smaller than the exposure failure value of the other image groups, and the exposure failure value is exceeded by the number of overexposed pixels in each of the image groups and a confidence The number of low pixels is determined, wherein the processor calculates a stereoscopic image of the object according to the image group corresponding to the optimal exposure condition. The exposure control device of claim 8, wherein the processor instructs the projector to sequentially project a structure having a plurality of scan patterns on the object to scan the object, wherein the structure having the scan patterns When the light is projected on the object, the processor instructs the image capturing device to capture a plurality of images of the object. The exposure control device of claim 9, wherein when a pixel has an exposure value greater than an exposure threshold in any of the image groups, determining the pixel is Overexposed pixels. The exposure control device of claim 9, wherein when a pixel has a confidence level in each of the image groups less than a confidence threshold, the pixel is judged to be too low in confidence. A pixel, wherein the confidence is a degree of change of an exposure value of the pixel in each of the image groups. The exposure control device of claim 9, wherein the exposure conditions are brightness of the projector, aperture of the image capture device, exposure time of the projector and the image capture device, or The intensity of the change in the scanned pattern. The exposure control device of claim 9, wherein the scan patterns comprise a specific pattern of a first spatial frequency and a second spatial frequency. The exposure control device of claim 9, wherein the structured light of each of the scan patterns has at least three different phase shifts, and each of the phase shifts respectively corresponds to one of the images.