Color image reproduction apparatus having a least squares look-up table augmented by smoothing

• US 4,941,039 A
• Filed: 04/04/1989
• Issued: 07/10/1990
• Est. Priority Date: 04/04/1989
• Status: Expired due to Term

• Current Assignee: Eastman Kodak Company
• Original Assignee: Eastman Kodak Company
• Inventors: E'Errico, John R.
• Primary Examiner(s): Groody, James J.
• Assistant Examiner(s): VU, KIM Y
• Application Number:
  US07/332,824
• Time in Patent Office: 462 Days
• Field of Search: 358/75, 358/78, 358/80, 358/428, 358/447, 364/526, 378/901
• US Class Current: 358/518
• CPC Class Codes: H04N 1/6019 using look-up tables H04N1/6025 takes precedence
• CPC Class Codes: H04N 1/6052 Matching two or more picture signal generators or two or more picture reproducers
• CPC Class Codes: H04N 1/6055 using test pattern analysis

Abstract

Color image reproduction apparatus, including a video monitor and a computer-based workstation, provides for reading a color image from an input film and for writing a reproduced image on an output film. A plurality of digitally operated look-up tables (LUTs), associated with the workstation, serve for transforming original imaging data to a common color space (CIELUV L* u* v*) and for transforming reproduced imaging data to different use-dependent RGB color spaces, e.g. video monitor, output film, etc. Output color image values stored in each LUT are computed off-line by means of a least squares algorithm applied to an input data set augmented by the second derivative of the function represented by the data set.

Claims

1. In imaging apparatus including an input device adapted to produce a multivariate signal representing an input image, a look-up table characterized by a series of discrete multivariate input signal values that are functionally related in a non-linear manner to a corresponding series of discrete reproduction signal values representative of useable output image information, and electronic computer means coupling said input device and said look-up table, for linearly interpolating between neighboring multivariate signal values in said look-up table in accordance with an actual multivariate signal provided by said input device, to compute a reproduction signal relating to an output image actually to be used, wherein the improvement comprises:

the discrete reproduction signal values, b_i, in said look-up table are computed by means of a least squares algorithm applied to the combination of (1) a first array of data, S, relating a series of values, Y, of a dependent variable of an input data set to the series of reproduction signal values to be computed for said look-up table, and (2) a second array of data, ρ

, relating a series of values of the second derivative of the non-linear function represented by the input data set, evaluated at selected input signal values, x_i, of said look-up table, to the series of reproduction signal values for said look-up table.

2. Imaging apparatus as defined in claim 1 wherein the least squares algorithm results in the series of reproduction signal values for said look-up table being computed from:

b_i =(S^T S+δ

² ρ

^T ρ

)^-1 S^T Y or its equivalent, where δ

is a smoothing parameter that determines the relative weight to be given the array of data ρ

.

3. In image composition apparatus including a scanner for scanning a photographic film to produce a tristimulous signal representative of colors in the film, a 3-dimensional look-up table characterized by a series of discrete tristimulous signal values and a corresponding series of discrete reproduction signal values which are functionally related in a non-linear manner to the series of tristimulous signal values and which are representative of colorants to be recorded on a particular photosensitive medium, and electronic computer means, coupling said scanner and said look-up table, for interpolating between neighboring tristimulous signal values in said look-up table as a function of an actual tristimulous signal produced by said scanner, to compute a reproduction signal relating colors in the film to colorants actually to be recorded on the photosensitive member, wherein the improvement comprises:

the discrete reproduction signal values, b_i, in said look-up table are computed by means of a least squares algorithm applied to the combinant of (1) a first array of data, S, relating a series of values, Y, of a dependent variable of an input data set to the series of reproduction signal values to be computed for said look-up table, and (2) a second array of data, ρ

, relating a series of values of the second derivative of the non-linear function represented by the input data set, evaluated at selected input signal values, x₁, of said look-up table, to the series of reproduction signal values for said look-up table.

4. Image composition apparatus as defined in claim 3 wherein the least squares algorithm results in the series of reproduction signal values for said look-up table being computed from:

(S^T S+δ

² ρ

^T ρ

)^-1 S^T Y or its equivalent, where δ

is a smoothing parameter that determines the relative weight to be given the array of data ρ

.