GB2253319A

GB2253319A - Photographic printing apparatus

Info

Publication number: GB2253319A
Application number: GB9104283A
Authority: GB
Inventors: Andrew David Hollows; Andrew George Minty
Original assignee: Durst
Current assignee: Durst
Priority date: 1991-02-28
Filing date: 1991-02-28
Publication date: 1992-09-02
Also published as: GB9104283D0

Abstract

A photographic negative or positive is illuminated by light of an adjustable colour eg from an enlarger head (4) and is observed by a video camera (7). The RGB signals are convened to digital form and then transformed using look-up tables in a personal computer (1), which produces on a monitor (10) a display of the illuminated image as it would be if it were to be used to produce a photographic print on paper having characteristics defined by the look-up tables. A small area A, B of the display is selected, compared with a reference image and its colour adjusted (manually or by feedback from the computer) to match that of the reference image. The reference image may be from another negative or it may be an area of some desired colour. Several different reference images may be used, separately compared with different small areas, the colour differences averaged and used to control the colour of the light. Once the colour of the light has been adjusted it may be used to produce a photographic print from the image, in the normal way. <IMAGE>

Description

Method and apparatus for Drocessina imaaes This invention relates to a method and an apparatus for processing images and especially, but not exclusively, for processing photographic images for the purpose of producing prints.

A problem facing photographic laboratories when printing photographs is to achieve a good match between prints which have been photographed under different lighting and background conditions. Two examples of where that problem can occur are wedding photography and product advertising-. In wedding photography lighting conditions vary enormously on the same film between bright sunshine, shade, and flashlight as photographs are taken outside and inside the church and at the reception. To make prints which match the bride's dress or groom's suit over all lighting conditions requires several test prints and a very skilled grading expert.

Similarly in product advertising the product will be photographed under different conditions and the product is often required to be exactly the same colour in all prints.

Two methods have been tried to solve the problem; negative scanning and video analysis.

Negative scanning involves testing many samples of colour over all the negative and making decisions as how best to print the negative; such systems are capable of producing good prints perhaps 70 to 90% of the time but are not capable of matching prints.

Video analysis involves producing a 'positive' colour image of the negative on a colour monitor via a video camera and an analogue negative/positive conversion box. The negative is illuminated with an enlarger style lamphouse in which red, green, blue, density can be independently controlled. The values RGBD are adjusted until the desired image is obtained on the monitor and these RGBD values are then translated to enlarger or printer control values to make the print. With video analysis systems good prints are obtained with a success rate of, perhaps, 80 to 90%. While some colour matching can be carried out in the process the results are not reliable because the eye's perception of colour depends on the background scene and these systems only offer a complete negative image on the screen.Some more sophisticated systems have a split image feature where half of the screen is the negative being analysed and the other half is a reference picture; while that gives better results it still suffers from the human perception problem and also that the colour response of the video system cannot be accurately adjusted to simulate the photographic paper response.

It is an object of the present invention to overcome the difficulty described above.

According to one aspect of the present invention there is provided a method of processing images including the steps of providing a first photographic image, illuminating the first image with a first light of adjustable colour, deriving three colour component signals representing the illuminated first image, converting the three colour component signals into digital signals, producing from the digital signals a first visible display representing a photographic print, the print being that obtained from the illuminated first image using photographic paper having particular characteristics, selecting a small area of the first display, comparing the colouring of the selected small area with that of a reference image, and providing adjustment signals to the first light of adjustable colour thereby to tend to bring the colouring of the selected small area to match that of the reference image.

According to a second aspect of the present invention there is provided apparatus for processing images including means for supporting a photographic image, a light source of adjustable colour for illuminating a photographic image held by the supporting means, video camera means focussed on the illuminated photographic image and producing three colour component signals representing that image, conversion means responsive to the three colour component signals to produce corresponding digital signals, transformation means receiving the digital signals and responsive to stored transformation data to produce transformed digital signals, digital to analogue conversion means receiving the transformed digital signals and producing transformed colour component signals, display means responsive to the transformed colour component signals to produce a visible display, the transformation of the digital signals being such that the display represents the illuminated photographic image as it would appear if printed on a photographic paper having particular characteristics, and digital computer means having operator input means, data storage means for storing at least a representation of a reference image, digital signal input means for receiving the digital signals from the conversion means, and digital signal output means connected to the digital to analogue conversion means and the display means, the digital computer being so programmed that there can be designated on the visible display a small area of the display selected by the operator using the operator input means, the apparatus further including means enabling the colour of the light source to be adjusted in response to a comparison of the colouring of the small area of the display with that of the reference image to bring the colouring of the selected small area of the display substantially to match that of the reference image.

The control of the colour of the light may be by the operator from his comparison of the colour of the selected small area of the display with the reference image or reference colour. That control may, on the other hand be automatic in response to the differences between the corresponding colour component signals of the selected small area of the display and of the reference colour; the operator may be permitted to make small adjustments to the colour of the light after it has been set automatically, for example, to take into account small variations in the colour over the selected small area.

The reference colour may be entered by the operator as values of the colour components, representing a particular colour. Alternatively, the reference colour or reference image may be derived from a selected small area of the display of another photographic image and then entered for later use. Preferably, a plurality of different reference colours and images may be stored for comparison with the colours of different selected small areas of the display of the first-mentioned photographic image.

The photographic image may be a colour negative or a colour positive.

An example of apparatus for processing photographic images will now be described with reference to the drawings of which: Figures 1 and 2 are diagrams to be used to explain the operation of the apparatus, Figure 3 is a block diagram of the apparatus, and Figure 4 is a diagram of the flow of data through the apparatus.

A block diagram of the apparatus is shown in Figure 3. It includes a personal computer 1 fitted with a number of rack boards 2 for performing different special functions which are connected to it by a bus system 3. A lamphouse 4 with filters 5 illuminates a photographic image 6, for example a colour negative, and a video camera 7 is focussed on the illuminated image. A keypad 8 and thumbwheels 9 are provided to enable an operator to make manual inputs into the computer 1 through one or more of the rack boards 2. A colour monitor 10 is provided for producing a display of the photographic image after processing. A liquid crystal data display 11 is also provided for displaying alphanumeric data and graphics separately from the monitor 10.

The rack boards 2 comprise boards 21 to 27, including three identical video boards 21, 22 and 23 respectively receiving the red, green and blue video signals from the camera 7. Those boards operate on-line to digitise the video signals and to transform the digital data using look-up-tables stored in random-access storage means on the boards to produce in digital form the image to be displayed on the monitor 10. The transformed image, or part of it, in digital form can be stored in a frame store forming part of the random-access storage of the computer 1. The look-up tables include the negative to positive transformation functions (if the image 6 is a negative), that is the characteristics of a photographic colour printing paper on which a print of the image is to be produced.The apparatus can also be used with a colour positive as the photographic image, in which case different look-up tables will be used. The random-access storage means on the boards 21, 22 and 23 can be accessed by the operator through the computer 1 to enable the look-up tables to be changed when required.

The boards 21, 22 and 23 also include digital to analogue converters operating on-line for producing from the transformed image in digital form or from data stored in the frame store the analogue signals for the monitor 10.

A sync (synchronising) board 24 controls the timing functions for the video signals from the camera 7 and to the monitor 10 synchronising the image transformation by the video boards 21, 22 and 23. The size and position of the overlay (frame) are also handled by this board.

An A/D (analogue to digital) board 25 receives voltage readings from photocells, photodiodes or phototransistors in the lamphouse 4 representing the amplitudes of the different colour components in its light output to the image 6 and converts them to digital form for adjusting the positions of the filters 5 to correct for any change in the light from the lamp in the lamphouse, due, for example, to a change in supply voltage. The digital values are stored for record purposes. The A/D board also includes the interface for the keypads. An expansion board has interface circuitry for the liquid crystal display 11 and four thumbwheel switches 9. The display 11 can display eight lines each of forty characters. The thumbwheel switches 9 are used for manual adjustment of the positions of the filters 5.

A stepper motor board 27 has four stepper motors together with limit switches and reference switch inputs.

Each stepper motor is coupled to drive a respective one of the filters (red, green, blue and density) 5 on the lamphouse 4. In the automatic mode of the apparatus, the computer 1 operates the stepper motors to adjust the colour of the light from the lamphouse 4 which illuminates the image 6. The stepper motors can also be operated in response to outputs from the thumbwheel switches 9.

The keypad 8, lamphouse 4, camera 7 and monitor 10 are all conventional items and perform the functions described below. In one example of the apparatus the camera is a Sony XC-711P colour RGB camera and the monitor is a Philips CM 8833 RGB monitor.

In the operation of the apparatus shown in Figure 3, a photographic image, for example a colour negative, is placed as shown at 6 to be illuminated by the light from the lamphouse 4. The positions of the four filters (red, green, blue and density) 5 are adjusted by the stepper motors under the control of the computer 1 in response to the voltage readings from the photocells in the lamphouse 4 so that the light illuminating the image is of the desired colour. The camera 7 produces red, green and blue video signals by scanning the illuminated image, and those signals are respectively applied to the video boards 21, 22 and 23. After digitising, the video signals are transformed using the stored look-up tables to red, green and blue digital signals and then to corresponding analogue signals for the display to be produced by the monitor 10.The transformations convert the colour negative image as it is scanned into a colour positive display having the colours which would be produced by printing the colour negative on a photographic printing paper having the characteristics represented by the look-up tables. The operator can enter the look-up tables in the random-access storage in the video boards 21, 22 and 23 through the computer 1 using the keypad 8.

When the image is displayed on the monitor 10, the operator can adjust its colours using the thumbwheels 9 respectively allocated to red, green, blue and density.

The adjustment of the thumbwheels 9 causes the computer 1 to drive the stepping motors to move the filters 5, thereby changing the colour of the light illuminating the image 6 and that, in turn, alters the colours of the image displayed on the monitor 10.

The computer 1 can generate patches on the displayed image, the patches being of position and size that are adjustable by the operator using the keypad 8. The patches may be very small, even consisting of a single picture element only; in such a case an additional display such as crossed lines or a small circle may be required to assist the operator in locating the patch.

The computer 1 also stores one or more reference colours and/or reference images. Under operator control a selected one of the reference colours or reference images can replace a selected one of the patches temporarily or be displayed beside that patch, so that the operator can judge how close the or each colour of the patch is to the reference colour or the colour(s) of the reference image.

In a manual mode of operation of the apparatus the operator can use the thumbwheels 9 to adjust the colour of the light so as to match the colour(s) of the patch to the reference colour.

The operator can select the size and position of a patch of the image displayed on the monitor 10. The colour of that patch, as represented by the averages of each colour component value taken over the picture elements within the patch, can be compared with a selected reference colour, as represented by the colour component values stored, and the respective differences between the corresponding colour component values used to operate the stepping motors automatically. The stepping motors move the filters 5 into and away from the path of light from the lamphouse 4, so that the colour of the patch is changed to match the reference colour. That constitutes an automatic mode of operation of the apparatus.

The apparatus displays the changing colour of the image enabling the operator to follow the adjustment of the colour of the displayed image and in particular the colour of the patch as it approaches the reference colour. The adjustment of the colour is performed in steps, the patch being scanned and its average colour, that is to say the colour of the individual picture elements in the patch being averaged over the patch, being compared with the reference colour or average colour of the reference image in the computer 1 to provide a step in that adjustment of the colour by movement of the filters 5.

The automatic matching can also be based on colour values other than the average taken over all the picture elements of the reference image and the patch as just described. For example, if the reference image and the patch to be matched to it, is of a strongly patterned subject, such as a polka dot material, then two colour values could be assigned to both the reference image and the patch, the values being the maximum RGB values and the minimum RGB values found at any position within the reference image and the patch. Two comparisons would then be performed, one between the maximum RGB values of the reference image and the patch and the other between the minimum RGB values of the reference image and the patch, and the average of the two differences used to adjust the colour of the light.Other representations of the properties of the patch and the reference image which could be used in place of the colour values could be based on spatial and statistical analysis of the colours within the two areas.

After the automatic adjustment, the operator can be enabled to use the thumbwheels 9 for additional adjustment of the colour, where, for example, some shading of the selected patch has an undesirable influence on the matching to the reference colour or reference image. In order to facilitate that additional adjustment the operator can cause the reference colour or reference image to be displayed beside or in place of the selected patch.

Figure 1 shows an example of a displayed image showing two patches A and B. The patches are of relatively small area, adjustable in size, and may be positioned by the operator on parts of the image of substantially uniform colour, so that it is reasonable to compare that colour with a reference colour. Other possible places where the patches may be positioned are commonly occurring features such as faces or on areas of patterned fabrics, in which cases the patches would be compared with reference images of the same face or the same fabric derived from another photographic image as described below. The reference colour or colours can be provided in two different ways. In the first way, each reference colour is represented by colour component values and these values are entered and stored in the computer as numbers.That is useful where, in an advertisement, for example, the colour of a particular part of the display image has to be exactly the correct colour. The reference colour may be one of a range of standard colours of which the colour component values are listed or stored in the computer memory.

The second way of providing the reference colour or colours is useful when a number of pictures of the same people are taken under different lighting conditions, for example, as at a wedding. In this case, a first negative is placed in the apparatus and the colour of the display image is adjusted by the operator using the thumbwheels 9. When he is satisfied, he places one or more patches on the image where the colour is substantially uniform and recurs in other pictures. Suppose that the picture is as shown in Figure 1 and patches A and B are chosen.

The colours of the patches A and B are selected as the reference colours by the operator and are stored in the computer 1. The operator now takes a second negative, for example, as in Figure 2, and puts it in the apparatus in place of the first. He then positions patches C and D as shown in Figure 2 and instructs the apparatus to match patch C to the first reference colour using the automatic mode described above. The operator may then match patch D to the second reference colour or he may use the thumbwheels 9 to adjust the colour until he is satisfied with the result. The computer may be arranged to take the average of the light colours needed to match the patches C and D respectively to the first and second reference colours. Figure 4 illustrates the flow of colour component data through the apparatus.

The technique just described is used for deriving and recording reference images. Examples of suitable subjects for reference images are faces and patterned fabrics as mentioned above. The automatic matching of colours of patches to reference images is effected by matching the average colours. Because of the colour variations within the patches and the reference images it is possible that the automatic matching may not produce a satisfactory result and the operator may be enabled to make further adjustment to the colour using the thumbwheels 9.

Once the colour of the light illuminating the photographic image has been adjusted to the operator's satisfaction a print may be prepared by focussing an image of the illuminated image on the printing paper.

The printing paper and a lens may be brought into position in place of the camera 7, or a mirror may be interposed in the light path between the image 6 and the camera 7 to reflect the light to the printing paper and the lens. The printing paper should, of course, have characteristics corresponding to the look-up tables stored in the computer.

In an alternative arrangement, the apparatus for determining the colour of light to be used to illuminate the photographic image may be separate from the printing and enlarging apparatus, the control of the colour of light to be used in the printing and enlarging process being effected in response to data provided by the firstmentioned apparatus and entered on records respectively attached to or otherwise associated with the photographic images. In that arrangement a single apparatus of the first-mentioned kind can service a plurality of printing and enlarging apparatus.

The apparatus can equally well be used to process colour positives instead of colour negatives using reversal printing paper, the look-up tables stored in the computer being changed accordingly.

An important feature of the apparatus is that the reference colours are stored as numbers and the comparisons of colours are effected by subtracting numbers in the computer, so that, although the representation of colours on the display on the monitor 10 may not be exact, the matching of colours, that is the matching of the colour of a selected patch to a reference colour, is exact.

Claims

CLAIMS:

1. A method of processing images including the steps of providing a first photographic image, illuminating the first image with a first light of adjustable colour, deriving three colour component signals representing the illuminated first image, converting the three colour component signals into digital signals, producing from the digital signals a first visible display representing a photographic print, the print being that obtained from the illuminated first image using photographic paper having particular characteristics, selecting a small area of the first display comparing the colouring of the selected small area with that of a reference image, and providing adjustment signals to the first light of adjustable colour thereby to tend to bring the colouring of the selected small area to match that of the reference image.

2. A method according to claim 1 wherein the selected small area of the display contains a commonly occurring feature or has substantially uniform colour or pattern

3. A method according to claim 1 or 2, wherein the adjustment signals for the first light of adjustable colour are produced by respectively comparing digital colour component signals representing the average colour of the reference image with corresponding digital colour component signals representing the average colour of the selected small area.

4. A method according to claim 1, 2 or 3 wherein the reference image is displayed beside the selected small area or intermittently in place of the selected small area and at least parts of the adjustment signals are entered by an operator observing the display.

5. A method according to any one of the preceding claims wherein the reference image is an area of a single colour and data identifying that colour is entered by an operator.

6. A method according to any one of claims 1 to 4 including the further steps of providing a second photographic image, illuminating the second image with a second light, deriving three colour component signals representing the illuminated second image, converting the three colour component signals into digital signals, producing from the digital signals a second visible display representing a photographic print obtained from the illuminated second image using a photographic paper having particular characteristics, selecting a small area of the second display, the selected small area containing a commonly occurring feature or having a substantially uniform colour or pattern, and storing a representation of the selected small area of the second display as the reference image.

7. A method according to claim 6 wherein the second light illuminating the second image is of adjustable colour and the method includes the further step of adjusting the colour of the second light so that the selected small area of the second display is of a desired colouring.

8. A method according to claim 6 or claim 7 including the further step of averaging the colour of the selected small area of the second display over that area to produce the reference image.

9. A method according to any one of the preceding claims wherein several different reference images are provided and the method includes comparing the different reference images with different selected small areas of the first display and adjusting the colour of the first light in response to the comparisons.

10. A method according to any one of the preceding claims wherein the or each photographic image is a colour negative.

11. A method according to any one of claims 1 to 9 wherein the or each photographic image is a colour positive.

12. Apparatus for processing images including means for supporting a photographic image, a light source of adjustable colour for illuminating a photographic image held by the supporting means, video camera means focussed on the illuminated photographic image and producing three colour component signals representing that image, conversion means responsive to the three colour component signals to produce corresponding digital signals, transformation means receiving the digital signals and responsive to stored transformation data to produce transformed digital signals, digital to analogue conversion means receiving the transformed digital signals and producing transformed colour component signals, display means responsive to the transformed colour component signals to produce a visible display, the transformation of the digital signals being such that the display represents the illuminated photographic image as it would appear if printed on a photographic paper having particular characteristics, and digital computer means having operator input means, data storage means for storing at least a representation of a reference image, digital signal input means for receiving the digital signals from the conversion means, and digital signal output means connected to the digital to analogue conversion means and the display means, the digital computer being so programmed that there can be designated on the visible display small area of the display selected by the operator using the operator input means, the apparatus further including means enabling the colour of the light source to be adjusted in response to a comparison of the colouring of the small area of the display with that of the reference image to bring the colouring of the selected small area of the display substantially to match that of the reference image.

13. Apparatus according to claim 12, wherein the apparatus is such that the reference image is displayed beside the selected small area or in place of the selected small area, and the means enabling the colour of the light source to be adjusted is operable by the operator.

14. Apparatus according to claim 12, wherein the computer is so programmed that it compares the average colour of the selected small area of the display with that of the stored reference image and the colour difference signals so produced are fed to the digital signal output means, that digital signal output means being connected to the means enabling the colour of the light source to be adjusted, the apparatus being such that the average colour of the selected small area of the display tends to be changed to match that of the stored reference image.

15. Apparatus according to claim 14 wherein the means enabling the colour of the light source to be adjusted includes operator usable input means to enable the operator to make additional adjustments to the colour of the light source.

16. Apparatus according to any one of claims 12 to 15, wherein the computer stores representations of a plurality of different reference images, and the computer is so programmed that it permits a plurality of different small areas to be selected by the operator, and different reference images to be associated with different selected small areas.

17. Apparatus according to claim 16 when dependent on claim 14 or 15, wherein the computer is so programmed that it averages the colour difference signals produced in response to the different selected small areas so as to provide output signals to the means for producing control signals for adjusting the colour of the light source.

18. Apparatus according to any one of claims 12 to 17, wherein a reference image is an area of a single colour and data identifying that colour can be entered by the operator.

19. Apparatus according to any one of claims 12 to 18, wherein the computer is so programmed to enable the operator to store the or each reference image by designating as the reference image a selected small area of a display produced in response to another illuminated photographic image.

20. Apparatus according to any one of claims 12 to 19 wherein the photographic image is a colour negative and the transformation data are such that they convert the colour component signals for each picture element of the negative into the corresponding colour component signals of a photographic print, taking into account any nonlinearities of the photographic printing process.

21. Apparatus according to any one of claims 12 to 19 wherein the photographic image is a colour positive and the transformation data are such that they convert the colour component signals for each picture element of the positive into the corresponding colour component signals of a photographic print, taking into account any nonlinearities of the photographic printing process.

22. Apparatus according to any one of claims 12 to 21 wherein the computer is so programmed that the operator can enter the characteristics of the printing paper to form the transformation data.

23. A method of processing images substantially as described herein and as illustrated by the accompanying drawings.

24. A method of producing a photographic print including adjusting the colour of the light source by a method according to any one of claims 1 to 11 and 23 and using the adjusted light source to illuminate the photographic image to produce the print.

25. A method of reproducing a photographic print including deriving values representing the adjusted colour of the light source obtained by a method according to any one of claims 1 to 11 and 23 and using the derived values to adjust the colour of another light source illuminating the photographic image to produce the print.

26. Apparatus for processing images substantially as described herein and as illustrated by the accompanying drawings.

27. Apparatus for producing a photographic print including apparatus according to any one of claims 11 to 21 and 24, and means for focussing an image of the illuminated photographic image on to photographic printing paper.