GB2169167A

GB2169167A - Obtaining monochromatic images from colour originals

Info

Publication number: GB2169167A
Application number: GB08520720A
Authority: GB
Inventors: Noriyuki Shimano; Shigeo Murakami
Original assignee: Dainippon Screen Manufacturing Co Ltd
Current assignee: Dainippon Screen Manufacturing Co Ltd
Priority date: 1984-12-21
Filing date: 1985-08-19
Publication date: 1986-07-02
Also published as: JPS61148959A; GB2169167B; DE3531339A1; DE3531339C2; GB8520720D0

Abstract

A colour original 1 is illuminated by differently coloured light sources 3R, 3G and 3B and light is reflected by the original 1 onto photosensitive means 5 e.g. an array of photosensitive devices, for a predetermined period, i.e. the integrating period, the output of which represents the integral of all the light falling on it during the integrating period. The period for which each source is on TR, TG and TB is controlled by control means 2, and by suitably varying the periods TR, TG and TB the output signal may be made to represent a monochromatic image, i.e. analysis of the colour image is performed by a system having the spectral sensitivity of the eye. <IMAGE>

Description

SPECIFICATION A Method of and Apparatus for Obtaining Image Information This invention relates to a method of and apparatus for obtaining image information.

Because of the increasing popularity of colour pictures, colour original images are increasingly being used for design, reproduction, printing and so forth.

One such use of color original images is the production of monochromatic reproductions. For example, elaborate reproductions are produced by colouring such monochromatic images in one of the warm colours to provide a design effect, or by using monochromatic grey images to provide variation of contrast effects.

Even where a grey image is available for use to provide the desired monochromatic grey image, a colour original image may be used to produce the desired grey reproduction when the original image is originally in colour.

Generally, in order to enable a monochromatic image to be produced from a colour image, many different colour compensatory filters, which produce a total spectral sensitivity corresponding to the spectral sensitivity of the human eye, are used in combination with a source of light illuminating the colour image to produce an image of the colour image on a photosensitive device or substrate, in order to attain a similar tonal property in the reproduction as in the colour image to provide an image as real as that obtained by looking directly at the colour original image with the naked eye.

Although, where many different colour compensatory filters are used, there is no problem when the tone of the original colour image is normal when the colour emission from the original colour image is uneven for example when there is a colour imbalance in the original colour image, or when a special modulation of reproduction is required, many filters of various tones must be provided, and the exchange of these filters takes much time and labour. Moreover, fading ofthe filter colours must be always taken into account.

It has also been proposed to scan a colour original image using two different wavelengths of laser light, and to control the ratio of enhancement, that is the intensity, of these beams in order to produce a desired monochromatic reproduction.

Where two different laser wavelengths are used, the equipment is expensive and it is hard to attain accurate correspondence of the modulated reproduction with the characteristics of human vision. In this method it is advantageous to use three different laser wavelengths, namely, red, green and blue for accurate modulation. However, in this case, the constitution of the electric circuit and the lighting systems are complicated, and the equipment becomes more expensive.

It is an object of the present invention to overcome or at least mitigate the above-mentioned problems.

According to one aspect of the present invention, there is provided a method of obtaining image information, which method comprises: illuminating a colour image; obtaining a plurality of differentcolour colour separation signals from the colour image; supplying each of the colour-separation signals to photosensitive means comprising a plurality of photosensitive devices for each receiving colour-separation signals over a predetermined period of time and for each then providing a signal representing the accumulated colour-separation signals received thereby in the said time period; and controlling the supply of the different-colour colour-separation signals to the photosensitive means during the said time period.

In a second aspect, the present invention provides apparatus for obtaining image information, which apparatus comprises: means for obtaining a plurality of different-colour colour-separation signals from a colour image; photosensitive means comprising a plurality of photosensitive devices for each receiving colour separation signals from a colour image over a predetermined period of time and for each then providing a signal representing the accumulated coiour-separation signals receiving thereby in the said time period; and means for controlling supply of colour-separation signals to the photosensitive means during the said time period.

The present invention also provides a method of obtaining image information, wherein: a colour original is illuminated by a plurality of light sources which have different main wavelengths, and have lighting periods which are controlled respectively in each integrating period of an array sensor formed of charge-coupled devices, so as to convert an optical image of the colour original formed on the array sensor by an optical system into electric signals for a monochromatic image.

The lighting periods of the light sources are advantageously synchronised with the integrating period of the charge-coupled devices, and the ratio of respective lighting periods are preferably freely variable within the range in which the maximum total exposure of the charge-coupled devices is less than the saturation exposure thereof. Conveniently, in one preferred arrangement, any variation of total exposure of the charge-coupled devices in each integrating period is compensated for by an amplifier.

In an alternative preferred arrangement, the total exposure of the charge-coupled devices in each integrating period is regulated to a constant value by modifying the lighting period of other lighting sources in response to the modification of the lighting period of a desired or selected lighting source.

The plurality of lighting sources may comprise red, green and blue light sources.

For a better understanding ofthe present invention, and to show how the same may be put into effect, reference will now be made, by way of example, to the accompanying drawings, in which: Figure 1 is a schematic block diagram of apparatus for carrying out a method in accordance with the invention; Figure 2 illustrates graphically respective the periods TR, TG and TB for which three light sources are on during a charging or integrating period of charge-coupled devices of photosensitive means of the apparatus shown in Figure 1; Figure 3 shows the spectral distribution curves for three lamps of different fundamental colours; Figure 4 shows a spectral sensitivity curve for the photosensitive means; and Figure 5 illustrates graphically a spectral response curve for the photosensitive means.

Referring now to the drawings, Figure 1 shows a block diagram of apparatus suitable for use in a method in accordance with the invention for obtaining image information to enable a monochromatic image to be produced from a colour image.

As shown in Figure 1, the apparatus comprises scanning apparatus for scanning a colour image 1.

The apparatus comprises three light sources of different colour (in the arrangement shown, a red (R) light source 3R, a green (G) light source 3G and a blue (B) light source 3B) for illuminating the colour image 1.A A lens 4 is provided to focus colour- separation signals from each light source which are either transmitted through or, as in the arrangement shown, reflected from the colour image 1 onto photosensitive means comprising an array 5 of photosensitive devices. The photosensitive devices are each arranged to receive, via the lens 4, light from the colour image over a predetermined period of time and to provide a signal representing the accumulated colour-separation signals received thereby in the said time period.In particular, the photosensitive devices may provide a signal representing the sum of the colour-separation signals received thereby in the said time period or an integral thereof over the said time period. The array 5 may comprise a linear array 5a of chargecoupled devices (CCD), or bucket-brigade devices (BBD) formed of metal oxide semiconductors (MOS).

The linear array 5 is arranged to scan the colour image 1, via the lens 4, in a main scanning direction, that is parallel to the linear array and, in the arrangement shown in Figure 1, in a direction extending perpendicularly of the plane of the paper.

The colour image 1 is scanned in a subsidiary scanning direction shown by the arrow A by effecting relative movement between any two of the array 5, the colour image 1 and the lens 4, for example by moving any one of the array 5, the lens 4 or the colour image 1 in the direction of the arrow A in Figure 1. Thus, the photosensitive array 5 is arranged to scan the entire colour image 1. The colour image 1 is scanned in the main scanning direction by reading the outputs of the photosensitive devices of the array 5 in series and, of course, the speed of scanning is synchronised with the said time period of the photosensitive devices so that the output of each photosensitive device is read at the end of the respective said time period.The optical image is thus converted into electrical signals at every movement in the main scanning direction by the respective photosensitive devices, so that the image signals can be read in one sweep.

A control circuit 2 controls the respective periods T, TB, TB for which the three light sources SR, SG, 3B are actuated or lit, that is the lighting periods thereof, as illustrated graphically in Figure 2, the lighting periods being synchronised with the main scanning speed within the said time period Tint of the photosensitive devices of the array 5 so as to obtain signals for a desired monochromatic image.

The response of a photosensitive device during the said time period to the light from the three sources is shown in Figure 5 and is given by the foilowing equations: E(A)=(fS(A) LH(A)dA} TR +ffS(A) LG(A)dA} T, + f rS(A) Ls(A)dA} TB (1) wherein: S(A) is a spectral sensitivity of the sensor 5; LR(A) is the spectral energy distribution of the source 3R of red light; LG(A) is the spectral energy distribution of the source 3G of green light; and LB(A) is the spectral energy distribution of the source 3B of blue light.

As the spectral response E of the photosensitive device 5 is a function of wave-length A, it is possible to modify the characteristics of the spectral response curve E(A) freely by selecting or modifying the time periods TR, TB, TB. Thus, if the time periods T,, TG and TB are appropriately selected, the spectral response curve E can be made to bear a close resemblance to the spectral response curve e of the human eye. The spectral response curve e of the human eye is shown in Figure 5. Alternatively, the spectral response curve E can be given a particular property or characteristic.For example, the spectral response E(A) for red light may be increased as indicated by the phantom line in Figure 5, as would be suitable for reproducing a reproduction image in warm colour by increasing the time period TR relative to the time periods TG and TB.

Where the spectral response curve E(A) has a close resemblance to the spectral response curve e of the human eye, the same modulations or variations of density are observed by the human eye for both the original colour image and the monochromatic reproduction so that the monochromatic reproduction gives a smooth and natural density variation or modulation without strangeness.

The so-called duty ratios TR/Tjnt, TB/Tint, TB/Tint between the respective lighting periods TR, TB, TB of the light sources 3R, 3G, 3B and the integrating time Tint can be varied appropriately to correct for over emission of colour or colour imbalance in the colour original. Thus, for example, when the colour original has a red cast, that is when the red component is too strong, the lighting period TR of the source of red light 3R may be reduced relative to the lighting periods TG and TB.

It is preferable that care is taken to ensure that the maximum total amount of light EMAX received by the array sensor 5a, that is the maximum exposure thereof, is kept less than the saturation exposure of the sensor, particularly when the lighting periods TRI TB, TB are varied, so as to prevent a blooming effect. However, any one or more of the lighting periods may be varied as desired.

Where the lighting period T,, TB, TB of each light source 3R, 3G, 3B is varied for the correction of over-emission of colour, that is where the colour image provides colour signals which are too strong, the total exposure in a said time period can be varied by AE to avoid saturation of the photosensitive devices, as well as the output level from the same sampling point.

In order to compensate for the variation of the output level or total exposure, the amplification factor K is controlled in accordance with the following equation (2), so that the gain G of the amplifier is kept constant: K=G(E+hE) (2) It is preferable in order to extend the dynamic range of the apparatus, that the maximum total amount of exposure EMAX of the photosensitive devices be chosen to be less than but near to the saturation exposure thereof. Therefore, it is preferable to vary the lighting periods of the other sources of lights, when the lighting period of a desired or selected source is varied, in response to the variation of the lighting period of the selected light source, so as to keep constant the maximum total amount of exposure EMAX of the photosensitive devices.

In a modified arrangement, only two light sources, for example the red and green light sources 3R and 3G, or any other different colour light sources (that is, light sources of different main or predominant wavelength) may be used and the lighting periods thereof controlled to obtain particular image signals to produce special effects in the monochromatic reproduction. Alternatively, it would of course, be possible to use more than three light sources, depending upon the predominant wavelength of the selected sources.

The light sources may comprise any suitable light sources, for example differently coloured (in the preferred arrangement, red, green and blue) lightemitting diodes.

Atwo-dimensional matrix sensor may be used in place of the one-dimensioned array sensor described above, in which case relative movement between the colour image 1, the sensor and the lens 4 may not be necessary, depending upon the size of the matrix.

Any kind of image pickup or photosensitive device having such a matrix sensor which receives a frame of an image at one go, such as a television camera, may be used.

Although in the arrangement described above, light sources of different main wavelengths are used to provide the colour-separation signals, it should be appreciated that appropriate filters could alternatively be used to produce the colourseparation signals. Also, the main wavelengths of the colour separation signals will, of course, depend upon the different-colour light sources or filters used and the colour-separation signals need not necessarily be red, green, blue.

The method and apparatus described above require only a few kinds of transmission filters of different main wavelengths; and thus the electrical circuitry and lighting system is simple and costeffective.

Claims

1. A method of obtaining image information, which method comprises: illuminating a colour image; obtaining a plurality of different colour colour-separation signals from the colour image; supplying each of the colour separation signals to photosensitive means comprising a plurality of photosensitive devices for each receiving colourseparation signals over a predetermined period of time and for each then providing a signal representing the accumulated colour-separation signals received thereby in the said time period; and controlling the supply of the different-colour colourseparation signals to the photosensitive means during the said time period.

2. A method according to Claim 1, wherein the supply of the different-colour colour-separation signals is controlled to vary the degree to which the photosensitive means is exposed to one or more of the different-colour colour-separation signals during the said time period.

3. A method according to Claim 1 or 2, wherein the supply of the different-colour colour-separation signals is controlled to vary a ratio between the different-colour colour-separation signals supplied to the photosensitive means during the said time period.

4. A method according to Claim 1,2 or 3, wherein the supply of the different-colour colour-separation signals is controlled to vary the time for which one or more of the different-colour colour-separation signals is supplied to photosensitive means during the said time period.

5. A method according to Claim 4, wherein the supply of the different-colour colour-separation signals is controlled to enable the ratio between the timeforwhich each different-colourcolourseparation signal is supplied to the photosensitive means and the said time period to be varied within a range up to, but not including, saturation of the photosensitive means.

6. A method according to any preceding claim, wherein the supply of the different-colour colourseparation signals is controlled to maintain a constant exposure of the photosensitive means during the said time period.

7. A method according to any one of Claims 1 to 5, in which a variation in the exposure of the photosensitive means is compensated for by amplifying means.

8. A method according to any preceding claim, wherein three different-colour colour-separation signals are obtained.

9. A method according to Claim 8, wherein the three colour-separation signals are red, green and blue.

10. A method according to any preceding claim, wherein the colour image is illuminated by a plurality of light sources o different colour to obtain the different-colour colour-separation signals.

11. A method according to any preceding claim, wherein the photosensitive means provides a signal representing a sum of the colour separation signals received thereby in the said time period.

12. A method according to any one of Claims 1 to 10, wherein the photosensitive means provides a signal representing an integral over the said time period of the colour-separation signals received by the photosensitive means in the said time period.

13. A method according to any preceding claim, wherein the photosensitive means and image are moved relative to one anotherto enable the photosensitive means to scan the entire image.

14. A method according to any preceding claim, wherein an array of photosensitive devices is used as the photosensitive means.

15. A method according to any one of Claims 1 to 13, wherein a matrix of photosensitive devices is used as the photosensitive means.

16. A method according to any preceding claim, wherein a plurality of bucket-brigade devices are used as the photosensitive means.

17. A method according to any preceding claim, wherein a plurality of metal oxide semiconductors are used as the photosensitive means.

18. A method according to any one of Claims 1 to 15, wherein a plurality of charge-coupled devices are used as the photosensitive means.

19. A method according to any preceding claim, wherein an optical system is used to supply the colour-separation signals to the photosensitive means.

20. A method according to any preceding claim, wherein the output of the photosensitive means is used to form a monochromatic image.

21. A method of obtaining image informations, wherein: a colour original is illuminated buy a plurality of light sources which have different main wavevengths, and have lighting periods which are controlled respectively in each integrating period of an array sensor formed of charge-coupled devices, so as to convert an optical image of the colour original formed on the array sensor by an optical system into electric signals for a monochromatic image.

22. A method according to Claim 21, wherein: the lighting periods of the light sources are synchronised with the integrating period of the charge coupled-devices and the ratio between the integrating period and each lighting period is varied freely within the range in which the maximum total exposure of charge-coupled devices is less than the saturation exposure thereof.

23. A method according to Claim 22, wherein the variation of the total exposure of the array sensor corresponding to the variation of the lighting period of the light sources is compensated for by amplifying means.

24. A method according to Claim 21 or 22, wherein the lighting periods of other sources of light are varied in response to the varying of the lighting period of a desired source of light so as to keep the total exposure of the array sensor constant.

25. A method according to any one of Claims 21 to 24, wherein the sources of light are red, green and blue light sources.

26. A method of obtaining image information substantially as hereinbefore described with reference to the accompanying drawings.

27. Apparatus for obtaining image information, which apparatus comprises: means for obtaining a plurality of different-colour colour separation signals from a colour image; photosensitive means comprising a plurality of photosensitive devices for each receiving colour-separation signals from a colour image over a predetermined period of time and for each then providing a signal representing the accumulated colour-separation signals received thereby in the said time period; and means for controlling supply of colour-separation signals to the photosensitive means during the said time period.

28. Apparatus according to Claim 27, wherein the controlling means is arranged to vary the degree to which the photosensitive means is exposed to one or more of the different-colour colour-separation signals during the said time period.

29. Apparatus according to Claim 27 or 28, wherein the controlling means is arranged to vary a ratio between the different-colour colour-separation signals supplied to the photosensitive means during the said time period.

30. Apparatus according to Claim 27, 28 or 29, wherein the controlling means is arranged to vary the time for which one or more of the differentcolour colour-separation signals is supplied to the photosensitive means during the said time period.

31. Apparatus according to Claim 30, wherein the controlling means is arranged to enable the ratio between the time for which each different-colour colour-separation signal is supplied to the photosensitive means and the said time period to be varied within a range up to, but not including, saturation of the photosensitive means.

32. Apparatus according to any one of Claims 27 to 31, wherein the controlling means is arranged to provide a constant exposure of the photosensitive means over the said time period.

33. Apparatus according to any one of Claims 27 to 31, wherein amplifying means are provided to compensate for a variation in the exposure of the photosensitive means.

34. Apparatus according to any one of Claims 27 to 33, wherein the obtaining means provides three different-colour colour-separation signals.

35. Apparatus according to Claim 34, wherein the three colour-separation signals are red, green and blue.

36. Apparatus according to any one of Claims 27 to 35, wherein the obtaining means comprises means for illuminating the colour image.

37. Apparatus according to Claim 36, wherein the illuminating means comprises a plurality of different-colour light sources.

38. Apparatus according to Claim 37, wherein the light sources are red, green and blue light sources.

39. Apparatus according to any one of Claims 27 to 38, wherein the photosensitive means is arranged to provide a signal representing a sum of the colour-separation signals received thereby in the said time period.

40. Apparatus according to any one of Claims 27 to 38, wherein the photosensitive means is arranged to provide a signal representing an integral over the said time period of the colour-separation signals received by the photosensitive means in the said time period.

41. Apparatus according to any one of Claims 27 to 40, wherein means are provided for moving the photosensitive means and the colour image relative to one another to enable the photosensitive means to scan the colour image.

42. Apparatus according to any one of Claims 27 to 41, wherein the photosensitive means comprises an array of photosensitive devices.

43. Apparatus according to any one of Claims 27 to 41, wherein the photosensitive means comprises a matrix of photosensitive devices.

44. Apparatus according to any one of Claims 27 to 43, wherein the photosensitive means comprises a plurality of bucket-brigade devices.

45. Apparatus according to any one of Claims 27 to 44, wherein the photosensitive means comprises a plurality of metal oxide semiconductor devices.

46. Apparatus according to any one of Claims 27 to 43, wherein the photosensitive means comprises a plurality of charge-coupled devices.

47. Apparatus according to any one of Claims 27 to 46, wherein optical means are provided to supply the colour-separation signals to the photosensitive means.

48. Apparatus according to any one of Claims 27 to 47, wherein the photosensitive means is arranged to provide a signal for forming a monochromatic image.

49. Apparatus for obtaining image information substantially as hereinbefore described, with reference to the accompanying drawings.

50. Apparatus for forming a monochromatic image from a colour image whenever incorporating apparatus in accordance with any one of Claims 27 to 49.

51. A monochromatic image whenever produced using a method in accordance with any one of Claims 1 to 26 and/or apparatus in accordance with any one of Claims 27 to 50.

52. Any novel feature or combination of features disclosed herein.