GB2158955A - Colour photography - Google Patents

Abstract

When taking a colour image, a reading is taken of the prevailing colour temperature and is recorded directly onto the film on which the photographic image itself is exposed. A camera is described having diffusers 26 through which the ambient light passes; it is then analysed by devices 28, before reaching film 10. The negative is developed in the usual way. When producing a positive from the negative by printing, the recorded colour temperature is read by the printer and used to modify the colour characteristics of the light source used, to compensate for the colour cast or bias prevailing at the time of exposure of the picture and to produce a positive which appears as though exposed under neutral white light. Also disclosed is a projector for projecting still or cine images which modifies the light source in response to the colour temperature recordings on the film adjacent the images. <IMAGE>

Description

SPECIFICATION Colour photography This invention is concerned with colour photography, and with the production on a positive photograph of a colour balance which is corrected relative to that prevailing at the time the negative was exposed. The intention is that a photographed scene taken under light other than neutral white light will appear in a positive print or on a screen as though it had been taken under neutral white light.

For the purposes of this specification, the terms "positive", "photograph" and "positive photograph" include photographic prints and projected images produced on a screen from a transparency or from a cine film.

Production of a positive from a colour negative requires a determination, from the colour tones on the negative, of the colour conditions (the "colour temperature") at the time the photograph was taken. This is because there is always a colour cast or bias in the ambient light at the time of taking a photograph which is different from the cast existing at another time or place. It is desirable to correct this cast, and to produce a positive which reproduces the scene photographed, as if the photograph had been taken under conditions without the colour cast, i.e. under neutral white light. To produce such a positive, the colour temperature has to be subjectively determined from the negative. In colour laboratories which process films automatically on a large scale, an averaging technique is used.

The processing machine looks at the negative and if the amount of transmitted light, or the contrast in the film falls between predetermined limits, a filter deemed to be appropriate to these conditions is switched in. This technique necessarily falls down on phtographs which do not meet the "average" criteria.

Examples of this failure are shots taken in incandescent light which tend to be printed with a reddish/yellow cast.

When negatives are developed individually, it is customary to make prints at a number of different settings and then subjectively to examine the results to determine which setting is most satisfactory. This is time consuming and wasteful of materials.

According to the invention, there is provided a method of producing a colour photograph, comprising the steps of: using a camera to record an image of an object on a photographic film, simultaneously obtaining a reading indicative of the colour temperature of the light illuminating the object, recording the colour temperature reading on the film at a fixed position relative to the position of the recorded image, developing the film to produce a negative of the object, making a positive from the negative, and in so doing reading the recorded colour temperature and using the recorded colour temperature to control the light source used to expose the positive.

The invention also provides a method of taking a photograph, including the steps of: using a camera to record an image of an object on a photographic film, simultaneously obtaining a reading indicative of the colour temperature of the light illuminating the object, and recording the colour temperature reading on the film at a fixed position relative to the position of the recorded image.

The invention further provides a method of producing a photographic positive from a film on which a colour temperature reading has been recorded, comprising the steps of: developing the film to produce a negative of the object, making a positive from the negative, and in so doing reading the recorded colour temperature and using the recorded colour temperature to control the light source used to expose the positive.

In yet another aspect of the invention, there is provided a camera including light receiving means situated outside the light path between the object being photographed and the film, the light receiving means being adapted to produce a signal representative of the colour temperature of the area surroundinq the object and means for putting a marking on the film adjacent the the image area on the film, the marking being indicative of the intensity of the signal.

Still another aspect of the invention provides apparatus for producing a colour photographic positive from a colour photographic negative, the apparatus comprising a light source, means for varying the colour composition of the light source, means for reading a marking on the negative indicative of the colour temperature at the time and place where the negative was exposed and means for using the markings on the negative to control the light source.

The invention thus allows a paper print to be produced from a negative or a projected image to be produced from a transparency, under light conditions which take account of the conditions occurring at the time the film was exposed. The light conditions at the printing stage can be individually set, automatically and/or electronically for each frame of a film, so that the correct light conditions are achieved for each exposure.

In another aspect, the invention extends to a projector for projecting either a moving picture or a still picture, the projector including a light source for illuminating a transparent film bearing an image and recorded colour temperature readings, and means for reading the recorded colour temperature and for adjusting the tone of the light source to compensate for a colour cast prevailing at the time of exposure of the film, as recorded on the film.

In a moving picture projector, it may be necessary to record the colour temperature readings on the film ahead of the picture frame to which they relate, to give the light source time to respond to the colour information.

The colour information can be analysed (i.e.

split into its three primary colours) in the camera before being recorded on the film. The information can be in the form of dots of colour (which are developed along with the picture) on a part of the film outside the picture area. Possible areas for this recordal are between the sprocket holes at the edge of a 35mm film, or between the picture frames.

The intensity of colour in each dot can indicate the proportion of that colour in the light illuminating the object being photographed, and can be read by the printing apparatus to reproduce the correct colour. However other methods of recording may be used. For example, a bar code could be printed on the film, or a magnetic strip could be included on the film and appropriate data could be recorded on the strip. The film could even be mechanically marked. An advantage of a developable marking however is that it will be subject to the same process conditions as the image itself, so if there are faults in the developing process leading to incorrect colour tones, these will also manifest themselves in the marking, and are likely to be automatically corrected, when the positive is produced using the colour information on the markings.

It may be desirable to provide a marking corresponding to each of the three primary colours in the relevant spectrum. When printing using transmitted light, these colours are red, green and blue. These colours produce their complement in the print.

Alternatively, only a single marking may be recorded on the film. This marking would reach the film through neutral white filters or diffusers, and would not be analysed in the camera but would be analysed in the processing apparatus which would thus include filters for splitting light transmitted through the single marking into its three primary colours, and means for responding to the analysed light.

It is also desirable to record the ambient level of white light at the time the film was exposed, to be used as a reference and as an indication of, the overall light level, for the purpose of exposure control, and this can be done with a fourth marking.

The camera used to take a photograph must be modified to allow the recording of the colour temperature. Preferably apertures are provided on the camera body, outside the path of light from the object to the film, and diffusers are mounted in these apertures so that a beam of diffused light enters the camera. This diffused beam is then analysed by being split into separate beams which are passed through filters each of which transmits one of the primary colours (e.g. a red filter transmits red and absorbs all other colours).

The light transmitted through the filters can then be transmitted by fibre optics directly to the film, where it can be incident on the film emulsion to leave a developable marking. Alternatively, the light transmitted by the filters can be sensed photoelectrically, and an electronic signal representative of the colour temperature can be produced and can be used to apply a marking to the film.

It may be possible to add to an existing camera a device which picks up and records the colour temperature, as described, and the invention extends to a fitting for a camera, the fitting being adapted to obtain a reading indicative of the colour temperature of the light illuminating an object being photographed and to record the colour temperature reading on the film in a fixed position relative to the position of the recorded image.

One type of printing apparatus (or enlarger) has three light sources representing the three primary colours, with the light from these sources being combined to produce white light. If the voltage applied to each of these light sources is controlled from the marking on the film, the light used to print from a developed film can be controlled to correct the colour cast prevailing at the time of exposure of the film. Alternatively, the light source may be provided with a filter or filters which are to be placed in the light path to alter the tone of the white light. The selection and placing of these filters in the light path can be controlled automatically using the information provided by the markings on the film.

There is very little space available on most films for recording additional data, since camera and film designers aim to put the largest possible picture area on to the film. However there is usually a small border between adjacent frames which could be used to record colour information. Also there is some area between the sprocket film transport holes which could be used. It may be difficult to obtain access to these positions, and it may be necessary to use reflecting surfaces to direct the light transmitted through the colour filters to its destination on the film.

The invention will now be further described, by way of example, with reference to the accompanying drawing, in which: Figure 1 shows a 35mm film layout; Figure 2 is a schematic representation of a camera according to the invention; and Figure 3 is a schematic diagram showing how colour information is recorded on the film.

A film 10, shown after developing, has a number of picture areas 1 2 and sprocket holes 14 along each edge. Before exposure, the complete film is uniformly coated with a light-sensitive emulsion which is thus applied also to the space between the picture areas and the space around and between the sprocket holes. In the developed film, the picture areas bear recorded images and the other areas of the film appear transparent.

In Figure 2, a camera 20 is being used to take a picture of a plant 22. The film 10 is positioned at the back of the camera, at the focal plane of the lens 24. At other positions on the camera body, light diffusers 26 are mounted over openings in the body. These openings are positioned where they will not be obscured by a photographer holding his camera in a normal way. The diffusers could be positioned within the camera, behind the openings. Light from the surroundings of the plant being photographed is incident on these diffusers, and is allowed to enter the camera body after having been diffused. This diffused light is then analysed inside the camera by devices generally indicated at 28, and a resultant colour temperature is recorded on the edges of the film 10.

With this arrangement, a retro-fit device can be provided for fitting to an existing camera, with a body carrying the diffusers 26 and the analysing devices 28 and mountable to a camera, probably at the back, to produce and record the colour information on the film.

Figure 3 shows how the analysing devices 28 operate. Light 30 from a variety of directions and of a variety of colours falls on the diffuser 26. After being diffused, this light is transmitted. The transmitted light is then split by optical means, possibly using four bundles of optical fibres, into four separate beams, which are all the same. Each beam 32 is passed to a filter 34. Three filters are shown, for red, blue and green light. The filtered light transmitted through these filters will be picked up by respective optical fibres 36 and directed to the edge of the film 10. White light will also be directed by a fibre 37 to the film. The light beams from the fibres 36,37 will then fall on the desired spots on the film to leave four markings 38. Alternative marking positions are also shown at 40.

Some form of shuttering device will be required so that the filtered light only falls on the film when the camera shutter is open to take a picture.

It may be possible to use light transmitted through the lens to provide the colour information, if diffusers are mounted on the Dshaped areas in the camera around the picture area. These areas result from the circular shape of the lens which transmits a circle of light towards the film plane. Since the film is rectangular, some unwanted light falls on the internal walls of the camera, in D-shaped areas bounded by a parabolic curve.

Alternative sites for light pick-up are around the periphery of the lens, or from positions on the outside of the lens housing.

Claims (28)

1. A method of producing a colour photograph, comprising the steps of: using a camera to record an image of an object on a photographic film, simultaneously obtaining a reading indicative of the colour temperature of the light illuminating the object, recording the colour temperature reading on the film at a fixed position relative to the position of the recorded image, developing the film to produce a negative of the object, making a positive from the negative, and in so doing reading the recorded colour temperature and using the recorded colour temperature to control the light source used to expose the positive.

2. A method of taking a photograph, including the steps of: using a camera to record an image of an object on a photographic film, simultaneously obtaining a reading indicative of the colour temperature of the light illuminating the object, and recording the colour temperature reading on the film at a fixed position relative to the position of the recorded image.

3. A method of producing a photographic positive from a film on which a colour temperature reading has been recorded, comprising the steps of: developing the film to produce a negative of the object, making a positive from the negative, and in so doing reading the recorded colour temperature and using the recorded colour temperature to control the light source used to expose the positive.

4. A camera including light receiving means situated outside the light path between the object being photographed and the film, the light receiving means being adapted to produce a signal representative of the colour temperature of the area surrounding the object and means for putting a marking on the film adjacent the the image area on the film, the marking being indicative of the intensity of the signal.

5. Apparatus for producing a colour photographic positive from a colour photographic negative, the apparatus comprising a light source, means for varying the colour composition of the light source, means for reading a marking on the negative indicative of the colour temperature at the time and place where the negative was exposed and means for using the markings on the negative to control the light source.

6. A projector for projecting either a moving picture or a still picture, the projector including a light source for illuminating a transpar ent film bearing an image and recorded colour temperature readings, and means for reading the recorded colour temperature and for adjusting the tone of the light source to compensate for a colour cast prevailing at the time of exposure of the film, as recorded on the film.

7. A projector as claimed in Claim 6 for projecting moving pictures, wherein the means for reading the recorded colour temperature is adapted to read the temperature from a part of the film ahead of the image being projected.

6. A method as claimed in Claim 1 or Claim 2, wherein the colour information is analysed (i.e. split into its three primary colours) in the camera before being recorded on the film.

9. A method as claimed in any one of Claims 1, 2 or 8, wherein the information is recorded in the form of dots of colour (which are developed along with the picture) on a part of the film outside the picture area.

10. A method as claimed in any one of Claims 1, 2, 8 or 9, wherein the colour temperature reading is recorded between the sprocket holes at the edge of a 35mm film.

11. A method as claimed in any one of Claims 1, 2, 8 or 9, wherein the colour temperature reading is recorded between the picture frames.

1 2. A method as claimed in Claim 9, wherein the intensity of colour in each dot indicates the proportion of that colour in the light illuminating the object being photographed, and can be read by the printing apparatus to reproduce the correct colour.

1 3. A method as claimed in any one of Claims 1, 2 or 8 to 1 2 wherein the colour temperature reading is recorded on the film using a bar code.

14. A method as claimed in any one of Claims 1, 2 or 8 to 12, wherein the colour temperature reading is recorded on the film using a magnetic strip.

1 5. A method as claimed in any one of Claims 1, 2 or 8 to 12, wherein the colour temperature reading is recorded on the film using a mechanically applied marking.

1 6. A method as claimed in any one of Claims 1, 2 or 8 to 15, wherein a marking is provided corresponding to each of the three primary colours in the relevant spectrum.

1 7. A method as claimed in any one of Claims 1, 2 or 8 to 15, wherein a single marking is recorded on the film.

18. A method as claimed in Claim 16, wherein a fourth marking is applied to the film to record the level of ambient white light at the time the film was exposed.

1 9. A camera as claimed in Claim 4, wherein apertures are provided on the camera body, outside the path of light from the object to the film, and diffusers are mounted in these apertures so that a beam of diffused light enters the camera.

20. A camera as claimed in Claim 1 9, including filters each of which transmits one of the primary colours.

21. A camera as claimed in Claim 20, wherein fibre optics are used to transmit the light through the filters directly to the film.

22. A camera as claimed in Claim 21, including means for photoelectrically sensing the light transmitted by the filters and means for producing an electronic signal representative of the colour temperature which can be used to apply a marking to the film.

23. A camera as claimed in any one of Claims 4 or 1 9 to 23, including reflecting surfaces to direct the light transmitted through the colour filters to its destination on the film.

24. Apparatus as claimed in Claim 5, having three light sources representing the three primary colours, with the light from these sources being combined to produce white light, and means for controlling the voltage applied to each of these light sources from the marking on the film.

25. Apparatus as claimed in Claim 5, wherein the light source is provided with a filter or filters which are to be placed in the light path to alter the tone of the white light, and wherein the selection and placing of these filters in the light path can be controlled automatically using the information provided by the markings on the film.

26. A fitting for a camera, the fitting being adapted to obtain a reading indicative of the colour temperature of the light illuminating an object being photographed and to record the colour temperature reading on the film in a fixed position relative to the position of the recorded image.

27. A method of producing a colour photograph, substantially as herein described with reference to the accompanying drawing.

28. A camera substantially as herein described, with reference to the accompanying drawing.