Calibration method for video image reproduction with electronic printer and video monitor

Claim 2

The system of claim 1 wherein said video image is a digital image, wherein said correcting means includes a first look-up table (LUT) for correcting the image applied to said video image printer and a second look-up table (LUT) for correcting the image applied to said video monitor and including digital to analog converter means (1) for converting said corrected image from said first LUT to an analog video image applied to said video image printer, and (2) for converting said corrected image from said second LUT to an analog video image applied to said video monitor.

Claim 3

The system of claim 1 wherein said video image printer is a cathode ray tube multiformat camera.

Claim 4

The system of claim 3 wherein said cathode ray tube multiformat camera (CRT MFC) includes brightness, contrast and density controls and wherein said first look-up table is generated as follows: printing a set of gray scale test patterns on film by means of said CRT MFC at preselected contrast and density control settings C₀ and D₀ and at incremental brightness settings B₁, B₂, B n ; measuring the density of film with a densitometer to determine the maximum film density, D max , for each brightness setting; from a plot of B vs. D max , selecting a desired D max and finding the brightness control setting B' to give the desired D max ; causing said CRT MFC to print on film the same said gray scale test pattern using brightness, contrast and density settings, respectively, of B', C₀ and D₀; with a densitometer, measuring the film density for each gray level and calculating intermediate densities using an interpolation technique; converting the set of density values into perceived lightness values using the formula where c₁ and c₂ are normalization constants, D f is film density, and p ≈ 1/3; constructing said first look-up tale from the measured and desired tone curves; wherein said monitor has brightness and contrast controls; and wherein said second look-up table is generated as follows: varying said brightness and contrast controls of said monitor to obtain, using a photometer, a desired minimum luminance, L min , and maximum luminance, L max , which correspond to minimum digital image value, CV=0, and maximum digital image value, CV=2 n -1, respectively; using a photometer, measuring the monitor luminance for each level of said gray scale test pattern used in constructing said first look-up table; calculating said monitor luminance for other digital image values, CV, using an interpolation technique; converting the monitor luminance values L m into perceived lightness values S m , using the visual perception characteristic formula S m = c₁(L m ) p + c₂ where c₁ and c₂ are normalization constants and p ≈ 1/3; and constructing said second look-up table from the measured and desired tone curves.