Browse Prior Art Database

SHADING / HISTOGRAM CIRCUIT

IP.com Disclosure Number: IPCOM000026661D
Original Publication Date: 1993-Feb-28
Included in the Prior Art Database: 2004-Apr-06
Document File: 2 page(s) / 86K

Publishing Venue

Xerox Disclosure Journal

Abstract

A shadinghistogram circuit 5 for a scanner which combines the functions of Charge Coupled Device (CCD) shading and histogram mapping in the same hardware is shown in Figure 1. Each CCD pixel Px requires two correction factors to make the individual pixels respond to light equally. The shading circuit 5 provides both offset 6 and gain correction 8 functions. The offset correction 6 subtracts a constant from each digitized CCD pixel Px. This corn ensates for residual offset voltages in the electronics and dark currents in

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XEROX DISCLOSURE JOURNAL

SHADING / HISTOGRAM CIRCUIT

Proposed Perry S. Bowen U.S. C1.358/461 Classification

Int. C1. H04N 1/00

P,

MX) Mapping cx*Fl prj%-r[

P, = raw digitized pixel

0, = offset corrected pixel C, = gain corrected pixel

8 by 8K 43-J '

t

M, = rnappedpixel

u

Mapped pixel M,

255

GREY

OUT

High Contrast

0

0 GREY IN 255

Corrected pixel Cx

XEROX DISCLOSURE JOURNAL - Vol. 18, No. 1 JanuarylFebruary 1993 83

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SHADING / HISTOGRAM CIRCUIT(Cont'd)

A shadinghistogram circuit 5 for a scanner which combines the functions of Charge Coupled Device (CCD) shading and histogram mapping in the same hardware is shown in Figure 1. Each CCD pixel Px requires two correction factors to make the individual pixels respond to light equally. The shading circuit 5 provides both offset 6 and gain correction 8 functions. The offset correction 6 subtracts a constant from each digitized CCD pixel Px. This corn ensates for residual offset voltages in the electronics and dark currents in

the

 E CD.
Then, gain correction 8, using a gain factor which is computed for each pixel, multiplies the offset correct pixel Ox by a number between 1 and 2. The gain factor compensates for gain variations from pixel to pixel since each pixel in

the CCD array responds to light differently. Weaker pixels are multiplied by a larger gain factor while stronger pixels are multiplied by a smaller gain factor. The gain factor is determined by a...