NAME
Image::Leptonica::Func::coloring
VERSION
version 0.04
coloring.c
coloring.c
Coloring "gray" pixels
PIX *pixColorGrayRegions()
l_int32 pixColorGray()
Adjusting one or more colors to a target color
PIX *pixSnapColor()
PIX *pixSnapColorCmap()
Piecewise linear color mapping based on a source/target pair
PIX *pixLinearMapToTargetColor()
l_int32 pixelLinearMapToTargetColor()
Fractional shift of RGB towards black or white
PIX *pixShiftByComponent()
l_int32 pixelShiftByComponent()
l_int32 pixelFractionalShift()
There are several "coloring" functions in leptonica.
You can find them in these files:
coloring.c
paintcmap.c
pix2.c
blend.c
enhance.c
They fall into the following categories:
(1) Moving either the light or dark pixels toward a
specified color. (pixColorGray)
(2) Forcing all pixels whose color is within some delta of a
specified color to move to that color. (pixSnapColor)
(3) Doing a piecewise linear color shift specified by a source
and a target color. Each component shifts independently.
(pixLinearMapToTargetColor)
(4) Shifting all colors by a given fraction of their distance
from 0 (if shifting down) or from 255 (if shifting up).
This is useful for colorizing either the background or
the foreground of a grayscale image. (pixShiftByComponent)
(5) Shifting all colors by a component-dependent fraction of
their distance from 0 (if shifting down) or from 255 (if
shifting up). This is useful for modifying the color to
compensate for color shifts in acquisition, for example
(enhance.c: pixColorShiftRGB).
(6) Repainting selected pixels. (paintcmap.c: pixSetSelectMaskedCmap)
(7) Blending a fraction of a specific color with the existing RGB
color. (pix2.c: pixBlendInRect())
(8) Changing selected colors in a colormap.
(paintcmap.c: pixSetSelectCmap, pixSetSelectMaskedCmap)
(9) Shifting all the pixels towards black or white depending on
the gray value of a second image. (blend.c: pixFadeWithGray)
(10) Changing the hue, saturation or brightness, by changing the
appropriate parameter in HSV color space by a fraction of
the distance toward its end-point. For example, you can change
the brightness by moving each pixel's v-parameter a specified
fraction of the distance toward 0 (darkening) or toward 255
(brightening). (enhance.c: pixModifySaturation,
pixModifyHue, pixModifyBrightness)FUNCTIONS
pixColorGray
l_int32 pixColorGray ( PIX *pixs, BOX *box, l_int32 type, l_int32 thresh, l_int32 rval, l_int32 gval, l_int32 bval )
pixColorGray()
Input: pixs (8 bpp gray, rgb or colormapped image)
box (<optional> region in which to apply color; can be NULL)
type (L_PAINT_LIGHT, L_PAINT_DARK)
thresh (average value below/above which pixel is unchanged)
rval, gval, bval (new color to paint)
Return: 0 if OK; 1 on error
Notes:
(1) This is an in-place operation; pixs is modified.
If pixs is colormapped, the operation will add colors to the
colormap. Otherwise, pixs will be converted to 32 bpp rgb if
it is initially 8 bpp gray.
(2) If type == L_PAINT_LIGHT, it colorizes non-black pixels,
preserving antialiasing.
If type == L_PAINT_DARK, it colorizes non-white pixels,
preserving antialiasing.
(3) If box is NULL, applies function to the entire image; otherwise,
clips the operation to the intersection of the box and pix.
(4) If colormapped, calls pixColorGrayCmap(), which applies the
coloring algorithm only to pixels that are strictly gray.
(5) For RGB, determines a "gray" value by averaging; then uses this
value, plus the input rgb target, to generate the output
pixel values.
(6) thresh is only used for rgb; it is ignored for colormapped pix.
If type == L_PAINT_LIGHT, use thresh = 0 if all pixels are to
be colored (black pixels will be unaltered).
In situations where there are a lot of black pixels,
setting thresh > 0 will make the function considerably
more efficient without affecting the final result.
If type == L_PAINT_DARK, use thresh = 255 if all pixels
are to be colored (white pixels will be unaltered).
In situations where there are a lot of white pixels,
setting thresh < 255 will make the function considerably
more efficient without affecting the final result.pixColorGrayRegions
PIX * pixColorGrayRegions ( PIX *pixs, BOXA *boxa, l_int32 type, l_int32 thresh, l_int32 rval, l_int32 gval, l_int32 bval )
pixColorGrayRegions()
Input: pixs (2, 4 or 8 bpp gray, rgb, or colormapped)
boxa (of regions in which to apply color)
type (L_PAINT_LIGHT, L_PAINT_DARK)
thresh (average value below/above which pixel is unchanged)
rval, gval, bval (new color to paint)
Return: pixd, or null on error
Notes:
(1) This generates a new image, where some of the pixels in each
box in the boxa are colorized. See pixColorGray() for usage
with @type and @thresh. Note that @thresh is only used for
rgb; it is ignored for colormapped images.
(2) If the input image is colormapped, the new image will be 8 bpp
colormapped if possible; otherwise, it will be converted
to 32 bpp rgb. Only pixels that are strictly gray will be
colorized.
(3) If the input image is not colormapped, it is converted to rgb.
A "gray" value for a pixel is determined by averaging the
components, and the output rgb value is determined from this.
(4) This can be used in conjunction with pixFindColorRegions() to
add highlight color to a grayscale image.pixLinearMapToTargetColor
PIX * pixLinearMapToTargetColor ( PIX *pixd, PIX *pixs, l_uint32 srcval, l_uint32 dstval )
pixLinearMapToTargetColor()
Input: pixd (<optional>; either NULL or equal to pixs for in-place)
pixs (32 bpp rgb)
srcval (source color: 0xrrggbb00)
dstval (target color: 0xrrggbb00)
Return: pixd (with all pixels mapped based on the srcval/destval
mapping), or pixd on error
Notes:
(1) For each component (r, b, g) separately, this does a piecewise
linear mapping of the colors in pixs to colors in pixd.
If rs and rd are the red src and dest components in @srcval and
@dstval, then the range [0 ... rs] in pixs is mapped to
[0 ... rd] in pixd. Likewise, the range [rs ... 255] in pixs
is mapped to [rd ... 255] in pixd. And similarly for green
and blue.
(2) The mapping will in general change the hue of the pixels.
However, if the src and dst targets are related by
a transformation given by pixelFractionalShift(), the hue
is invariant.
(3) For inplace operation, call it this way:
pixLinearMapToTargetColor(pixs, pixs, ... )
(4) For generating a new pixd:
pixd = pixLinearMapToTargetColor(NULL, pixs, ...)pixShiftByComponent
PIX * pixShiftByComponent ( PIX *pixd, PIX *pixs, l_uint32 srcval, l_uint32 dstval )
pixShiftByComponent()
Input: pixd (<optional>; either NULL or equal to pixs for in-place)
pixs (32 bpp rgb)
srcval (source color: 0xrrggbb00)
dstval (target color: 0xrrggbb00)
Return: pixd (with all pixels mapped based on the srcval/destval
mapping), or pixd on error
Notes:
(1) For each component (r, b, g) separately, this does a linear
mapping of the colors in pixs to colors in pixd.
Let rs and rd be the red src and dest components in @srcval and
@dstval, and rval is the red component of the src pixel.
Then for all pixels in pixs, the mapping for the red
component from pixs to pixd is:
if (rd <= rs) (shift toward black)
rval --> (rd/rs) * rval
if (rd > rs) (shift toward white)
(255 - rval) --> ((255 - rs)/(255 - rd)) * (255 - rval)
Thus if rd <= rs, the red component of all pixels is
mapped by the same fraction toward white, and if rd > rs,
they are mapped by the same fraction toward black.
This is essentially a different linear TRC (gamma = 1)
for each component. The source and target color inputs are
just used to generate the three fractions.
(2) Note that this mapping differs from that in
pixLinearMapToTargetColor(), which maps rs --> rd and does
a piecewise stretching in between.
(3) For inplace operation, call it this way:
pixFractionalShiftByComponent(pixs, pixs, ... )
(4) For generating a new pixd:
pixd = pixLinearMapToTargetColor(NULL, pixs, ...)
(5) A simple application is to color a grayscale image.
A light background can be colored using srcval = 0xffffff00
and picking a target background color for dstval.
A dark foreground can be colored by using srcval = 0x0
and choosing a target foreground color for dstval.pixSnapColor
PIX * pixSnapColor ( PIX *pixd, PIX *pixs, l_uint32 srcval, l_uint32 dstval, l_int32 diff )
pixSnapColor()
Input: pixd (<optional>; either NULL or equal to pixs for in-place)
pixs (colormapped or 8 bpp gray or 32 bpp rgb)
srcval (color center to be selected for change: 0xrrggbb00)
dstval (target color for pixels: 0xrrggbb00)
diff (max absolute difference, applied to all components)
Return: pixd (with all pixels within diff of pixval set to pixval),
or pixd on error
Notes:
(1) For inplace operation, call it this way:
pixSnapColor(pixs, pixs, ... )
(2) For generating a new pixd:
pixd = pixSnapColor(NULL, pixs, ...)
(3) If pixs has a colormap, it is handled by pixSnapColorCmap().
(4) All pixels within 'diff' of 'srcval', componentwise,
will be changed to 'dstval'.pixSnapColorCmap
PIX * pixSnapColorCmap ( PIX *pixd, PIX *pixs, l_uint32 srcval, l_uint32 dstval, l_int32 diff )
pixSnapColorCmap()
Input: pixd (<optional>; either NULL or equal to pixs for in-place)
pixs (colormapped)
srcval (color center to be selected for change: 0xrrggbb00)
dstval (target color for pixels: 0xrrggbb00)
diff (max absolute difference, applied to all components)
Return: pixd (with all pixels within diff of srcval set to dstval),
or pixd on error
Notes:
(1) For inplace operation, call it this way:
pixSnapCcmap(pixs, pixs, ... )
(2) For generating a new pixd:
pixd = pixSnapCmap(NULL, pixs, ...)
(3) pixs must have a colormap.
(4) All colors within 'diff' of 'srcval', componentwise,
will be changed to 'dstval'.pixelFractionalShift
l_int32 pixelFractionalShift ( l_int32 rval, l_int32 gval, l_int32 bval, l_float32 fraction, l_uint32 *ppixel )
pixelFractionalShift()
Input: rval, gval, bval
fraction (negative toward black; positive toward white)
&ppixel (<return> rgb value)
Return: 0 if OK, 1 on error
Notes:
(1) This transformation leaves the hue invariant, while changing
the saturation and intensity. It can be used for that
purpose in pixLinearMapToTargetColor().
(2) @fraction is in the range [-1 .... +1]. If @fraction < 0,
saturation is increased and brightness is reduced. The
opposite results if @fraction > 0. If @fraction == -1,
the resulting pixel is black; @fraction == 1 results in white.pixelLinearMapToTargetColor
l_int32 pixelLinearMapToTargetColor ( l_uint32 scolor, l_uint32 srcmap, l_uint32 dstmap, l_uint32 *pdcolor )
pixelLinearMapToTargetColor()
Input: scolor (rgb source color: 0xrrggbb00)
srcmap (source mapping color: 0xrrggbb00)
dstmap (target mapping color: 0xrrggbb00)
&pdcolor (<return> rgb dest color: 0xrrggbb00)
Return: 0 if OK, 1 on error
Notes:
(1) This does this does a piecewise linear mapping of each
component of @scolor to @dcolor, based on the relation
between the components of @srcmap and @dstmap. It is the
same transformation, performed on a single color, as mapped
on every pixel in a pix by pixLinearMapToTargetColor().
(2) For each component, if the sval is larger than the smap,
the dval will be pushed up from dmap towards white.
Otherwise, dval will be pushed down from dmap towards black.
This is because you can visualize the transformation as
a linear stretching where smap moves to dmap, and everything
else follows linearly with 0 and 255 fixed.
(3) The mapping will in general change the hue of @scolor.
However, if the @srcmap and @dstmap targets are related by
a transformation given by pixelFractionalShift(), the hue
will be invariant.pixelShiftByComponent
l_int32 pixelShiftByComponent ( l_int32 rval, l_int32 gval, l_int32 bval, l_uint32 srcval, l_uint32 dstval, l_uint32 *ppixel )
pixelShiftByComponent()
Input: rval, gval, bval
srcval (source color: 0xrrggbb00)
dstval (target color: 0xrrggbb00)
&ppixel (<return> rgb value)
Return: 0 if OK, 1 on error
Notes:
(1) This is a linear transformation that gives the same result
on a single pixel as pixShiftByComponent() gives
on a pix. Each component is handled separately. If
the dest component is larger than the src, then the
component is pushed toward 255 by the same fraction as
the src --> dest shift.AUTHOR
Zakariyya Mughal <zmughal@cpan.org>
COPYRIGHT AND LICENSE
This software is copyright (c) 2014 by Zakariyya Mughal.
This is free software; you can redistribute it and/or modify it under the same terms as the Perl 5 programming language system itself.