Color photoprinting with a scanning memory mask

A color contact printer for exposing opaque photographic material to photographic images by scanning said images with a plurality of cathode ray tubes (CRT's), said printer comprising:

• a. a light source having first, second and third CRT's, said first CRT having a red emitting phospor screen, the second a green emitting phospor screen, and the third a blue emitting phospor screen, said light source also having a projecting lens for each CRT to enable the combined beams from the three CRTs to be focussed into a single scanning spot;
• b. at least one photosensor means for measuring a portion of the light from the scanning spot after it has been modulated by the photographic image, to generate a density related signal therefrom;
• c. a first memory scan means for scanning said photographic image, said memory scan means having a first control means responsive to said density related signal to modify the effective contrast range and exposure level of said scanning spot, said memory scan means further having a storage means for storing the modified density related signals obtained during the memory scan, said signals representing a density corrected luminous mask of said image;
• d. carriage means for bringing said opaque photographic material into intimate contact with said photographic image after completion of said memory scan;
• e. exposure scan means for exposing said photographic material with said scanning spot, said exposure scan having a second control means responsive to the modified density-related signal stored in said storage means to superimpose upon said imaging scan a luminous mask of the image obtained during the memory scan, said exposure scan thereby having a corrected exposure level and corrected contrast excursion range, for exposing said photographic material.

A color contact printer for exposing an opaque photographic material from a color original with a scanning spot light source, said printer comprising:

• a. CRT means for scanning said color original with a scanning spot of light, said means having separate gain controls for adjusting the relative intensity of the three primary colors of light to be generated by said means;
• b. at least one photosensor means for measuring the light passing through said color original to generate density-related signals therefrom;
• c. prescan means responsive to said density-related signals for modulating said scanning spot to modify the effective contrast range and exposure level of said density-related signals, said means generating during prescan a D.sub.min signal representative of the minimum density of said color original, a D.sub.max signal representative of the maximum density of said color original, a .DELTA.D signal representative of the difference between D.sub.min and D.sub.max, and a D.sub.sum exposure level signal;
• d. comparative circuit means for automatically comparing the .DELTA.D signal to a preset value representative of the contrast acceptance range of said opaque photographic material to be exposed, said means generating thereby a contrast excursion range signal;
• e. memory scan means for scanning said original with said scanning spot and storing a modified density-related signal generated thereby in an image storage tube, said scanning spot being modified by said .DELTA.D signal and said D.sub.sum signal during said memory scan to generate a density corrected luminous mask of said original;
• f. means for bringing said opaque photographic material into intimate contact with said color original after completion of said memory scan;
• g. exposure scan means for exposing said opaque photographic material with said scanning spot after it has passed through said color original, said exposure means responsive to said stored, modified, density-related signal to generate an exposing scan having a density-corrected luminous mask superimposed thereon to alter the exposing effect of said beam spot and thereby provide a density corrected image on said opaque photographic material.

A method of automatically modifying the exposure level and contrast excursion limits for a color contact printer wherein an opaque photographic receiving media is used, said method comprising:

• a. positioning a color original to be duplicated over a scanning spot light source, said light source having means to vary the respective blue, red and green components of said light;
• b. prescanning said original with said scanning spot while measuring the light passing through the original to determine its minimum and maximum density, the maximum density of the material, the difference between said minimum and maximum densities (.DELTA.D) and its average density;
• c. comparing the .DELTA.D value to a predetermined reference value to generate a scanning spot control signal, said reference value representing the maximum contrast acceptance limits of said photographic receiving media;
• d. memory scanning the original while simultaneously (1) modulating the scanning spot with said control signal, and (2) recording the light level passing through the original in a memory storage means, said controlled modulation being effective to alter the contrast excursion limits and determine the exposure level required, said modulated light level representing a modified luminous mask of the original to be duplicated;
• e. positioning said opaque photographic receiving media over said color original and in intimate contact therewith;
• f. exposing said opaque photographic receiving media with said scanning spot while modulating said spot with the luminous mask signal stored in said memory storage means, whereby the exposure level and contrast excursion limits of said exposure are retained within the predetermined contrast excursion limits of the opaque photographic receiving media.