Browse Prior Art Database

Digital Color Decompression Circuit

IP.com Disclosure Number: IPCOM000034312D
Original Publication Date: 1989-Feb-01
Included in the Prior Art Database: 2005-Jan-27
Document File: 3 page(s) / 63K

Publishing Venue

IBM

Related People

Barrera, DD: AUTHOR [+3]

Abstract

In today's video cameras the input illumination is captured in a nonlinear format. Error is introduced when using this nonlinear (compressed) format for averaging or mixing calculations. A hardware circuit is suggested to decompress or linearize the digital color image data to reduce error before averaging or mixing of the pel data occurs. A compressed or nonlinear format is used to represent the captured image data. The image compression format takes away quantization resolution from the higher intensity areas resulting in no visual degradation of the image when displayed on a CRT monitor. (Image Omitted) Averaging or mixing of pels while in this compressed format causes some error due to the gray-scale nonlineararity of the data.

This text was extracted from a PDF file.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 55% of the total text.

Page 1 of 3

Digital Color Decompression Circuit

In today's video cameras the input illumination is captured in a nonlinear format. Error is introduced when using this nonlinear (compressed) format for averaging or mixing calculations. A hardware circuit is suggested to decompress or linearize the digital color image data to reduce error before averaging or mixing of the pel data occurs. A compressed or nonlinear format is used to represent the captured image data. The image compression format takes away quantization resolution from the higher intensity areas resulting in no visual degradation of the image when displayed on a CRT monitor.

(Image Omitted)

Averaging or mixing of pels while in this compressed format causes some error due to the gray-scale nonlineararity of the data. The proposed circuit suggests a method of decompressing the pel data in hardware to a linear format first before averaging or mixing of data to eliminate the error due to nonlinearity of the data. Fig. 1 shows a graph of illumination (E) input to the camera and the compressed output (Y) from the camera as given by this formula Y = E**.45. The dashed line in Fig. 1 shows the compressed (C) input to the circuit shown in Fig. 2 and the uncompressed (U) output of the circuit as given by the formulas below. IF C = 0-15 THEN U=C

IF C = 16-47 THEN U = ((C-16)*2)+16 = 2C=16

IF C = 48-63 THEN U = ((C-48)*3)+81 = 3C-63

where C = compressed data (6 bits)

U = uncompressed data (7 bits) All values in Fig. 1 have been normalized. The dashed line represents a 3-line approximation to an ideal inverse function of the compressed camera output function
(Y). T...