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Two-Dimensional Luminance Compression

IP.com Disclosure Number: IPCOM000040001D
Original Publication Date: 1987-Sep-01
Included in the Prior Art Database: 2005-Feb-01
Document File: 3 page(s) / 64K

Publishing Venue

IBM

Related People

Bellinghausen, JM: AUTHOR [+2]

Abstract

This article describes a two dimensional luminance compression technique for compressing a captured image of a discrete color document. A discrete color document is one having luminance and chrominance values which are intended to be constant throughout well-defined areas. Most business documents fall in this category. The compression technique operates on captured data after that data has been filtered and thresholded to remove unintended variations in luminance or chrominance values. The original data is preferably stored in memory in logical lines with each logical line consisting of a series of paired values. One value in each pair is the luminance (Y) of the run. The other value is the pel position (P) at the end of the run.

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Two-Dimensional Luminance Compression

This article describes a two dimensional luminance compression technique for compressing a captured image of a discrete color document. A discrete color document is one having luminance and chrominance values which are intended to be constant throughout well-defined areas. Most business documents fall in this category.

The compression technique operates on captured data after that data has been filtered and thresholded to remove unintended variations in luminance or chrominance values. The original data is preferably stored in memory in logical lines with each logical line consisting of a series of paired values. One value in each pair is the luminance (Y) of the run. The other value is the pel position (P) at the end of the run. The abbreviations used in describing the technique are: CL - current line CR - current run PP - position pointer HL - history (preceding) line SOR - start of run HR - history run Y - luminance value PR - previous run on same line YS - Y stack P - pel position at end of run The compression technique uses a number of special transmision symbols, defined below: SYMBOL DEFINITION Defines Luminance and Run Length
SYSP Y(CR) = Y(HR); P(CR) = P(HR); and SOR(CR) > or = SOR(HR).

SYL1 As for SYSP, except P(CR) 1 pel left of P(HR).

SYR1 As for SYSP, except P(CR) 1 pel right of P(HR).

SYDP As for SYSP, except no correlation between P(CR) and P(HR).

DYSP Y(CR) <> Y(HR); P(CR) = P(HR); and SOR(CR) > or = SOR(HR).

DYL1 As for DYSP, exept P(CR) 1 pel left of P(HR).

DYR1 As for DYSP, exept P(CR) 1 pel right of P(HR). Defines Luminance Values Only

SYDP Y(CR) = Y(HR) but no correlation between P(CR) and P(HR).

B1 Y(CR) = Y(PR-1).

B2 Y(CR) = Y(PR-2).

NY New luminance header. New Y defined by next six bits. Defines Run Length Values Only L1 - L5 Run lengths one to five bits long.

L31 Run length header for runs 5 < RUN < 32. Actual run length defined by next 5 bits.

L63 Run length header for runs 31 < RUN < 64. Actual run length defi...