Abstract: Apparatus for performing a color transformation or color retouch operation on multibit digital data defining P color components of image pixels. The apparatus comprises a look-up table (2) which is addressed by N most significant bits (MSBS) of each color component value and which contains coarse versions of output pixel color component values. An interpolator (3) is responsive to M least significant bits (LSBS) of each color component value to interpolate fine versions of the output pixel values from the coarse output pixel values obtained from the look-up table. A processor loads coarse output pixel data for each color component into the 2.sub.NP addresses of the look-up table which may be addressed by the M MSBs of the input pixel data. The processor (8) is adapted to cause the value of N progressively to increase with successive iterations.

Abstract: Image display apparatus comprises a display monitor; an image frame buffer for storing data defining the color content of pixels of an image; and a control system for selecting from the frame buffer for each pixel displayed on the monitor the appropriate pixel data from the frame buffer. The relationship between the monitor pixels and the frame buffer pixels is defined by a preselected composite linear function, wherein the control system determines the frame buffer pixels corresponding to the monitor pixels by applying the preselected composite linear function in a stepwise manner.

Abstract: A method and apparatus for interactively modifying an image defined by original digital data, representing the color content of pixels of the image at a first resolution. The apparatus comprises a first store (4;12) for storing the digital data of the pixels at the first resolution; a monitor (9); a digitizing table (5); and an image processor (6;13,15). The image processor (6;13,15) is responsive to signals from the digitizing table (5) to select a modification algorithm and a portion of the image stored in the first store (4;12) to which the algorithm is to be applied.

Abstract: Digital signals are generated for each pixel of an image to be reproduced, corresponding to the values of color components in each pixel. The respective color component values of each pixel are applied to a set of look-up tables (30) so loaded that they recognize whether the color component values of a pixel fall within a color range(s) for which a processing operation is to be carried out. The look-up tables provide an output signal representing one of a number of possible processing operations for that pixel, in the form of an operation number. The operation number signal is applied through a processor (32) to an operation select table (36) which converts the operation number into a specific processing operation for each color component. The processing operations may be retouching, image retention (no change), replacement by a tint value, or dropout.