Method of and apparatus for establishing a reference point on a gradation correction curve
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United States of America Patent
Stats
-
Jan 8, 1991
Grant Date -
N/A
app pub date -
Dec 5, 1989
filing date -
Dec 9, 1988
priority date (Note) -
Expired
status (Latency Note)
Importance
Abstract
A highlight point (HL.sub.R, HL.sub.G, HL.sub.B) and/or a shadow point (SD.sub.R, SD.sub.G, SD.sub.B) on a gradation correction curve are established in consideration of decoloration and color fog of an original. Density values of respective primary colors are obtained for each pixel on an original. Average density is computed for each pixel and a cumulative histogram of average density distribution is generated. Temporary reference density values corresponding to prescribed cumulative frequencies are found on the cumulative histogram. Reference color density values (D.sub.RH, D.sub.GH, D.sub.BH) are computed by averaging the density of each color for the pixels having average density between the temporary reference density and terminal density on the cumulative histogram. The highlight and shadow points are specified with one of the reference color density values.
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