GB2049965A - Device for determining filter settings and printing photographic colour negatives - Google Patents

Abstract

A device for printing photographic colour negatives, comprising a photocell unit which by means of an optical fibre receives light from an unexposed part of the negative film and measures its colour values. A calculating and setting unit determines the filter settings to be used in printing. The filter adjustments are therefore determined on the basis of the measurements made on the unexposed part of the developed negative.

Description

SPECIFICATION Device for printing photographic colour negatives The invention relates to a device for printing photographic colour negatives, comprising a device for measuring the colour values of the film to be printed to determine the filter settings to be used upon printing. Such printing devices are used extensively by printing agencies.

The filter settings to be used depend upon several factors. A first factor is the type of paper to be used for printing. Usually, this is not varied, so that it would be possible to use constant filter settings as far as this factor is concerned.

However, a second factor which determines the desirable filter settings is the type of film being handled. Since printing agencies are confronted with a large variety of brands and types of film, while the colour values of the negative of different brands and types of film are widely varying, separate filter adjustments are necessary for each brand and type of film. For this reason, the colour values of each negative to be printed are usually measured, and by means of the resulting measurements, the filter settings to be used for printing that negative are determined.

The measurements are influenced not only by the properties of the brand and type of film concerned, but equally by the type of picture.

Dependent upon the main feature of the picture (blue sky, green pasture, yellow beach), but also dependent upon the type of light used during the exposure (day light, flash light, incandescent light, candle light) a certain colour will often be predominant or lacking in the colour negative, and this influences the resulting measurements and thereby the filter Settings selected, without real justification. There is no cause, for example, to suppress the colour blue by means of a certain filter adjustment if the picture to be printed largely conisists of a blue sky. For that reason, extremely complicated measuring devices have been developed, which are able to determine automatically whether a certain colour is predominant or lacking for good reason, and which, if that is the case, refrain from making any correction.Measuring devices have also been developed which taken into account only the measured overall density of each negative, and which do not respond to certain colours being predominant or lacking. Such devices, however, are suitable only for printing negatives of a certain brand and type of film, since the colour values of different brands and types of film differ widely, even if the pictures are otherwise identical. Such devices must be switched for other brands and types of film, for which reason they cannot handle different brands and types of film without the execution of a separate adjustment for each film.

The invention aims to provide a device of the type described above, which is able to handle any brand and type of film, provided is has been developed in the proper way, without it being necessary to execute a specific adjustment for each brand and type of film. The brand and type of film need not even be known at all.

The invention is based upon the recognition that colour slide films, provided they are not out of date, have been stored and exposed in a reasonable way and have been developed correctly, invariably provide pictures with an acceptable colour balance, without any correction being necessary. Since such films are developed with a standard process (the process used obviously having been matched to the brand and type of film) correction is in fact not even possible.

Therefore, the same result can be expected of the colour negative image proper of a colour negative film. Here again, the colour negative image exhibits an acceptable colour balance, provided that the film is not out of date, has been stored and exposed in a reasonable way, and has been developed properly. The fact that, nevertheless, entirely different filter settings are necessary fpr printing different brands and types of film, in order to obtain a good colour balance of the prints, is due exclusively to the fact that colour negative films as distinct from colour slide films, are provided with a colour mask which arises during development, the colour of which is widely varying for different brands and types of film.

A good colour baiance of the print is therefore ensured if upon printing, filter settings are selected which compensate for the presence of the colour mask. The colour mask in its pure form (not influenced by the negative images on the film) is present on unexposed parts of the developed film, and therefore a measurement of unexposed parts of the developed film provides results which can be used for determining filter adjustments which compensate colour mask of the film.

According to the present invention there is provided a device for use in printing photographic colour negatives, comprising a measuring device for the colour values of the film to be printed, which produces signals for determining the filter settings to be used upon printing, the measuring device being arranged to receive light from an unexposed part of the developed film and determine the filter adjustments on the basis of the measuring results on the said unexposed part.

Since in this way, the colour mask of any brand or type of film can be fully compensated for, without it being necessary even to know the brand and type, such a device can, provided they have been developed properly, handle all brands and types of film intermingled, without any coding of the films to be handled or any hand adjustment necessary.

Unexposed parts of the film are available on the end parts of each film, between each pair of adjacent images on each film, and alongside the image sequence of each film. Therefore, all these film parts are suitable for the measurement.

However, it must be taken into account that at certain locations alongside the image sequence of each film, code indications of the brand and type of film are usually present, which can undesirably influence the results of the measurements if they are accidentally taken at such a code location.

Apart from the above measurement for obtaining a correction for the influence of the colour mask, a measurement of the density of the various negative images can be executed in the usual way if desired, for obtaining a correction for overexposure or underexposure of the negative image concerned, and moreover colour measurements can be executed on the negative images, in order to introduce a correction by adjustment of the filter settings for the fact that certain colours are predominant or lacking in the picture, caused, for example, by the type of light used for the exposure.

An embodiment of the invention will now be described with reference to the accompanying drawings of which: Fig. 1 shows a fragmentary view of a short length of film; and Fig. 2 shows in diagrammatic form a device for measuring the colour values of a colour negative film in accordance with the invention.

Referring to Fig. 1 this shows a short length of exposed and developed colour negative film 1, which in the case shown is of the 35 mm type, although other sizes of film are equally suitable.

This film is provided with the usual two rows of sprocket perforations 2, which are, of course, not suitable for the measurement intended. Neither are the exposed frames 3, since they contain the developed negative images in addition to the basic colour mask. All other regions of the film, with the obvious exception of the very first part which has been grossly overexposed when loading the camera, are basically suitable for the measurement intended. However, it is preferred not to use the margins between either two of sprocket perforations 2 and the film edge, since these margins usually contain indications of the film brand and film type, which would falsify the measurement if the measurement was inadvertantly taken at the exact location of such an indication.More suitable locations for the intended measurement are the narrow strips between the long sides of the frames 3 and either row of sprocket perforations 2, the narrow strips between the short sides of successive frames 3, the region between the two rows of sprocket perforations 2 in the initial part of the film from the end of the part which has been grossly overexposed when loading the camera to the start of the first frame or at the end of the film between the two rows of sprocket perforations 2 from the end of the last frame 3 to the very end of the film.

A device for effecting the measurements may be set up as shown in Fig. 2.

The film 1 is illuminated by a light source 4 which can be the same light source as is used for projecting the images in the film frames onto the light sensitive material during printing. Light passing through the film at any of the suitable locations as explained in connection with Fig. 1 is picked up by an optical fibre 5 which is positioned so as to select only the light passing through the desired location on the film. Alternatively, a lens system can be used for this purpose. The light thus selected is fed to a photocell unit 6 containing three photocells, each of which is sensitive to light of a different colour. These three photocells provide three corresponding electric output signals 7, the magnitude of which represent both the absolute and relative transmission of the measurement location on the film for each of the three measurement colours.

Therefore, the three electrical output signals 7 to.gether are representative of the colour as well as the density of the colour mask on the film. These signals are applied to a calculating and setting unit 8 which derives the necessary filter adjustments for printing from these signals. The unit 8 therefore provides three setting signals 9, each of which adjusts the filter setting for one particular colour. Therefore, the filter settings are automatically adjusted so as to compensate for the colour mask on the film.

Both the photocell unit 6 and the calculating and setting unit 8 are known devices. the design of which need not be explained here in detail.

Claims (6)

1. A device for use in printing photographic colour negatives, comprising a measuring device for the colour values of the film to be printed, which produces signals for determining the filter settings to be used upon printing, the measuring device being arranged to receive iight from an unexposed part of the developed film and determine the filter adjustments on the basis of the measuring results on the said unexposed part.

2. A device according to claim 1, in which the measuring device is arranged to make a measurement on an unexposed part of the header of each film.

3. A device according to claim 1, in which the measuring device is arranged to make a measurement on an unexposed part between two images of each film.

4. A device according to claim 1, in which the measuring device is arranged to make a measurement on an unexposed part alongside the image sequence of each film

5. A method of determining the filter settings to be used for printing from colour negative film comprising measuring the colour values of an unexposed part of the film to be printed.

6. A device for use in printing photographic colour negative substantially as hereinbefore described with reference to the accompanying drawings.