Anti-clipping color-image correction
Computer-based, anti-clipping, pre-printing, color-image correction via virtual color-parameter controllers that are provided within the graphic user interface of a print drier. Parameters accommodated include Red, Green and Blue offset, Lightness offset, Gamma and Chroma. Chroma modifications are handled preliminarily by a special mathematical matrix. In one embodiment of the invention, matrix-processed Chroma values are directly inserted into an algorithm, and are then co-processed with other parameter modifications within an anti-clipping, hyperbolic-tangent-function (asymptotic-like) algorithm which implements an asymptotic-like approach toward creating final pixel modification values that avoid range-limit color and/or tone-scale clipping. In another embodiment of the invention, matrix-processed Chroma values are additionally inserted in to such an algorithm as components of a pair of like cubic terms. These cubic terms function to enhance asymptotic behavior of the algorithm in certain situations. Final pixel values are drawn from three one-dimensional look-up tables, one for each of the three colors. These tables which, save overall computational time, are based upon prior user approval of a low-pixel-count sub-sampled preview image of the whole, larger, original image, in which preview image the expected effects of color parameter changes are observable.
1. A computer-based image-manipulation method for enabling anti-clipping, selective user control over a color-affecting parameter in a computer-presented color image which is intended to be printed, where clipping is defined by the occurrence of an unintended condition, based upon user control input, wherein that parameter assumes a value which lies outside a desired value range which is directly associated with the computer-recognized number value range of 0–255, said method comprising:
furnishing suitable computer-responsive, change-value color controls that are selectively manipulable by a user to effect changes, ultimately, in such a parameter value, thus to vary a certain characteristic of color in the image, and
applying predetermined governance over the actual value of the color-affecting parameter, including (a) implementing preliminary matrix processing of a user-chosen Chroma value, followed by (b) implementing for each respective color-space color, an anti-clipping algorithm in accordance with the algorithmic formula expressed as follows:
OUTPUT
=
255
4
(
[
1
+
TANH
(
[
INPUT
+
Δ
L
-
128
-
G
+
Δ
R
]
/
G
)
]
+
[
1
+
TANH
(
[
INPUT
+
Δ
L
-
128
+
G
+
Δ
R
]
/
G
)
]
)
whereby, no matter the input control implemented by the user, that user chosen value is constrained in relation to approaching either one of the two limit values in the mentioned range to an asymptotic-like approach toward such limit value.
2. The method of claim 1 , wherein the application of governance involves inserting a selected, matrix-processed Chroma value directly into the mentioned anti-clipping algorithm.
3. The method of claim 1 , wherein said furnishing of controls includes providing individual controllers each relating to at least one of the collection of color parameters drawn from the list including (a) Red, Green and Blue color offset, (b) Lightness offset, (c) Chroma, and (d) Gamma.
4. The method of claim 1 , wherein the algorithmic formula expressed as follows:
OUTPUT
=
255
4
(
[
1
+
TANH
(
[
INPUT
+
Δ
L
-
128
-
G
+
Δ
R
]
/
G
)
]
+
[
1
+
TANH
(
[
INPUT
+
Δ
L
-
128
+
G
+
Δ
R
]
/
G
)
]
)
is modified as expressed by the modifified algorithmic formula as follows:
(
255
4
)
(
[
1
+
TANH
(
[
(
INPUT
-
128
)
+
B
(
INPUT
-
128
)
3
+
Δ
L
-
G
+
Δ
R
]
/
G
)
]
+
[
1
+
TANH
(
[
(
INPUT
-
128
)
+
B
(
INPUT
-
128
)
3
+
Δ
L
+
G
+
Δ
R
]
/
G
)
]
)
.
5. The method of claim 4 , wherein said applying of governance involves inserting a selected, matrix-processed Chroma value directly into the mentioned modified algorithmic formula.
6. The method of claim 4 , wherein said furnishing of controls includes providing individual controllers each relating to at least one of the collection of color parameters drawn from the list including (a) Red, Green and Blue color offset, (b) Lightness offset, (c) Chroma, and (d) Gamma.