NAME
Image::Leptonica::Func::warper
VERSION
version 0.04
warper.c
warper.c
High-level captcha interface
PIX *pixSimpleCaptcha()
Random sinusoidal warping
PIX *pixRandomHarmonicWarp()
Helper functions
static l_float64 *generateRandomNumberArray()
static l_int32 applyWarpTransform()
Version using a LUT for sin
PIX *pixRandomHarmonicWarpLUT()
static l_int32 applyWarpTransformLUT()
static l_int32 makeSinLUT()
static l_float32 getSinFromLUT()
Stereoscopic warping
PIX *pixWarpStereoscopic()
Linear and quadratic horizontal stretching
PIX *pixStretchHorizontal()
PIX *pixStretchHorizontalSampled()
PIX *pixStretchHorizontalLI()
Quadratic vertical shear
PIX *pixQuadraticVShear()
PIX *pixQuadraticVShearSampled()
PIX *pixQuadraticVShearLI()
Stereo from a pair of images
PIX *pixStereoFromPair()FUNCTIONS
pixQuadraticVShear
PIX * pixQuadraticVShear ( PIX *pixs, l_int32 dir, l_int32 vmaxt, l_int32 vmaxb, l_int32 operation, l_int32 incolor )
pixQuadraticVShear()
Input: pixs (1, 8 or 32 bpp)
dir (L_WARP_TO_LEFT or L_WARP_TO_RIGHT)
vmaxt (max vertical displacement at edge and at top)
vmaxb (max vertical displacement at edge and at bottom)
operation (L_SAMPLED or L_INTERPOLATED)
incolor (L_BRING_IN_WHITE or L_BRING_IN_BLACK)
Return: pixd (stretched), or null on error
Notes:
(1) This gives a quadratic bending, upward or downward, as you
move to the left or right.
(2) If @dir == L_WARP_TO_LEFT, the right edge is unchanged, and
the left edge pixels are moved maximally up or down.
(3) Parameters @vmaxt and @vmaxb control the maximum amount of
vertical pixel shear at the top and bottom, respectively.
If @vmaxt > 0, the vertical displacement of pixels at the
top is downward. Likewise, if @vmaxb > 0, the vertical
displacement of pixels at the bottom is downward.
(4) If @operation == L_SAMPLED, the dest pixels are taken from
the nearest src pixel. Otherwise, we use linear interpolation
between pairs of sampled pixels.
(5) This is for quadratic shear. For uniform (linear) shear,
use the standard shear operators.pixQuadraticVShearLI
PIX * pixQuadraticVShearLI ( PIX *pixs, l_int32 dir, l_int32 vmaxt, l_int32 vmaxb, l_int32 incolor )
pixQuadraticVShearLI()
Input: pixs (8 or 32 bpp, or colormapped)
dir (L_WARP_TO_LEFT or L_WARP_TO_RIGHT)
vmaxt (max vertical displacement at edge and at top)
vmaxb (max vertical displacement at edge and at bottom)
incolor (L_BRING_IN_WHITE or L_BRING_IN_BLACK)
Return: pixd (stretched), or null on error
Notes:
(1) See pixQuadraticVShear() for details.pixQuadraticVShearSampled
PIX * pixQuadraticVShearSampled ( PIX *pixs, l_int32 dir, l_int32 vmaxt, l_int32 vmaxb, l_int32 incolor )
pixQuadraticVShearSampled()
Input: pixs (1, 8 or 32 bpp)
dir (L_WARP_TO_LEFT or L_WARP_TO_RIGHT)
vmaxt (max vertical displacement at edge and at top)
vmaxb (max vertical displacement at edge and at bottom)
incolor (L_BRING_IN_WHITE or L_BRING_IN_BLACK)
Return: pixd (stretched), or null on error
Notes:
(1) See pixQuadraticVShear() for details.pixRandomHarmonicWarp
PIX * pixRandomHarmonicWarp ( PIX *pixs, l_float32 xmag, l_float32 ymag, l_float32 xfreq, l_float32 yfreq, l_int32 nx, l_int32 ny, l_uint32 seed, l_int32 grayval )
pixRandomHarmonicWarp()
Input: pixs (8 bpp; no colormap)
xmag, ymag (maximum magnitude of x and y distortion)
xfreq, yfreq (maximum magnitude of x and y frequency)
nx, ny (number of x and y harmonic terms)
seed (of random number generator)
grayval (color brought in from the outside;
0 for black, 255 for white)
Return: pixd (8 bpp; no colormap), or null on error
Notes:
(1) To generate the warped image p(x',y'), set up the transforms
that are in getWarpTransform(). For each (x',y') in the
dest, the warp function computes the originating location
(x, y) in the src. The differences (x - x') and (y - y')
are given as a sum of products of sinusoidal terms. Each
term is multiplied by a maximum amplitude (in pixels), and the
angle is determined by a frequency and phase, and depends
on the (x', y') value of the dest. Random numbers with
a variable input seed are used to allow the warping to be
unpredictable. A linear interpolation is used to find
the value for the source at (x, y); this value is written
into the dest.
(2) This can be used to generate 'captcha's, which are somewhat
randomly distorted images of text. A typical set of parameters
for a captcha are:
xmag = 4.0 ymag = 6.0
xfreq = 0.10 yfreq = 0.13
nx = 3 ny = 3
Other examples can be found in prog/warptest.c.pixSimpleCaptcha
PIX * pixSimpleCaptcha ( PIX *pixs, l_int32 border, l_int32 nterms, l_uint32 seed, l_uint32 color, l_int32 cmapflag )
pixSimpleCaptcha()
Input: pixs (8 bpp; no colormap)
border (added white pixels on each side)
nterms (number of x and y harmonic terms)
seed (of random number generator)
color (for colorizing; in 0xrrggbb00 format; use 0 for black)
cmapflag (1 for colormap output; 0 for rgb)
Return: pixd (8 bpp cmap or 32 bpp rgb), or null on error
Notes:
(1) This uses typical default values for generating captchas.
The magnitudes of the harmonic warp are typically to be
smaller when more terms are used, even though the phases
are random. See, for example, prog/warptest.c.pixStereoFromPair
PIX * pixStereoFromPair ( PIX *pix1, PIX *pix2, l_float32 rwt, l_float32 gwt, l_float32 bwt )
pixStereoFromPair()
Input: pix1 (32 bpp rgb)
pix2 (32 bpp rgb)
rwt, gwt, bwt (weighting factors used for each component in
pix1 to determine the output red channel)
Return: pixd (stereo enhanced), or null on error
Notes:
(1) pix1 and pix2 are a pair of stereo images, ideally taken
concurrently in the same plane, with some lateral translation.
(2) The output red channel is determined from @pix1.
The output green and blue channels are taken from the green
and blue channels, respectively, of @pix2.
(3) The weights determine how much of each component in @pix1
goes into the output red channel. The sum of weights
must be 1.0. If it's not, we scale the weights to
satisfy this criterion.
(4) The most general pixel mapping allowed here is:
rval = rwt * r1 + gwt * g1 + bwt * b1 (from pix1)
gval = g2 (from pix2)
bval = b2 (from pix2)
(5) The simplest method is to use rwt = 1.0, gwt = 0.0, bwt = 0.0,
but this causes unpleasant visual artifacts with red in the image.
Use of green and blue from @pix1 in the red channel,
instead of red, tends to fix that problem.pixStretchHorizontal
PIX * pixStretchHorizontal ( PIX *pixs, l_int32 dir, l_int32 type, l_int32 hmax, l_int32 operation, l_int32 incolor )
pixStretchHorizontal()
Input: pixs (1, 8 or 32 bpp)
dir (L_WARP_TO_LEFT or L_WARP_TO_RIGHT)
type (L_LINEAR_WARP or L_QUADRATIC_WARP)
hmax (horizontal displacement at edge)
operation (L_SAMPLED or L_INTERPOLATED)
incolor (L_BRING_IN_WHITE or L_BRING_IN_BLACK)
Return: pixd (stretched/compressed), or null on error
Notes:
(1) If @hmax > 0, this is an increase in the coordinate value of
pixels in pixd, relative to the same pixel in pixs.
(2) If @dir == L_WARP_TO_LEFT, the pixels on the right edge of
the image are not moved. So, for example, if @hmax > 0
and @dir == L_WARP_TO_LEFT, the pixels in pixd are
contracted toward the right edge of the image, relative
to those in pixs.
(3) If @type == L_LINEAR_WARP, the pixel positions are moved
to the left or right by an amount that varies linearly with
the horizontal location.
(4) If @operation == L_SAMPLED, the dest pixels are taken from
the nearest src pixel. Otherwise, we use linear interpolation
between pairs of sampled pixels.pixStretchHorizontalLI
PIX * pixStretchHorizontalLI ( PIX *pixs, l_int32 dir, l_int32 type, l_int32 hmax, l_int32 incolor )
pixStretchHorizontalLI()
Input: pixs (1, 8 or 32 bpp)
dir (L_WARP_TO_LEFT or L_WARP_TO_RIGHT)
type (L_LINEAR_WARP or L_QUADRATIC_WARP)
hmax (horizontal displacement at edge)
incolor (L_BRING_IN_WHITE or L_BRING_IN_BLACK)
Return: pixd (stretched/compressed), or null on error
Notes:
(1) See pixStretchHorizontal() for details.pixStretchHorizontalSampled
PIX * pixStretchHorizontalSampled ( PIX *pixs, l_int32 dir, l_int32 type, l_int32 hmax, l_int32 incolor )
pixStretchHorizontalSampled()
Input: pixs (1, 8 or 32 bpp)
dir (L_WARP_TO_LEFT or L_WARP_TO_RIGHT)
type (L_LINEAR_WARP or L_QUADRATIC_WARP)
hmax (horizontal displacement at edge)
incolor (L_BRING_IN_WHITE or L_BRING_IN_BLACK)
Return: pixd (stretched/compressed), or null on error
Notes:
(1) See pixStretchHorizontal() for details.pixWarpStereoscopic
PIX * pixWarpStereoscopic ( PIX *pixs, l_int32 zbend, l_int32 zshiftt, l_int32 zshiftb, l_int32 ybendt, l_int32 ybendb, l_int32 redleft )
pixWarpStereoscopic()
Input: pixs (any depth, colormap ok)
zbend (horizontal separation in pixels of red and cyan
at the left and right sides, that gives rise to
quadratic curvature out of the image plane)
zshiftt (uniform pixel translation difference between
red and cyan, that pushes the top of the image
plane away from the viewer (zshiftt > 0) or
towards the viewer (zshiftt < 0))
zshiftb (uniform pixel translation difference between
red and cyan, that pushes the bottom of the image
plane away from the viewer (zshiftb > 0) or
towards the viewer (zshiftb < 0))
ybendt (multiplicative parameter for in-plane vertical
displacement at the left or right edge at the top:
y = ybendt * (2x/w - 1)^2 )
ybendb (same as ybendt, except at the left or right edge
at the bottom)
redleft (1 if the red filter is on the left; 0 otherwise)
Return: pixd (32 bpp), or null on error
Notes:
(1) This function splits out the red channel, mucks around with
it, then recombines with the unmolested cyan channel.
(2) By using a quadratically increasing shift of the red
pixels horizontally and away from the vertical centerline,
the image appears to bend quadratically out of the image
plane, symmetrically with respect to the vertical center
line. A positive value of @zbend causes the plane to be
curved away from the viewer. We use linearly interpolated
stretching to avoid the appearance of kinks in the curve.
(3) The parameters @zshiftt and @zshiftb tilt the image plane
about a horizontal line through the center, and at the
same time move that line either in toward the viewer or away.
This is implemented by a combination of horizontal shear
about the center line (for the tilt) and horizontal
translation (to move the entire plane in or out).
A positive value of @zshiftt moves the top of the plane
away from the viewer, and a positive value of @zshiftb
moves the bottom of the plane away. We use linear interpolated
shear to avoid visible vertical steps in the tilted image.
(4) The image can be bent in the plane and about the vertical
centerline. The centerline does not shift, and the
parameter @ybend gives the relative shift at left and right
edges, with a downward shift for positive values of @ybend.
(6) When writing out a steroscopic (red/cyan) image in jpeg,
first call pixSetChromaSampling(pix, 0) to get sufficient
resolution in the red channel.
(7) Typical values are:
zbend = 20
zshiftt = 15
zshiftb = -15
ybendt = 30
ybendb = 0
If the disparity z-values are too large, it is difficult for
the brain to register the two images.
(8) This function has been cleverly reimplemented by Jeff Breidenbach.
The original implementation used two 32 bpp rgb images,
and merged them at the end. The result is somewhat faded,
and has a parameter "thresh" that controls the amount of
color in the result. (The present implementation avoids these
two problems, skipping both the colorization and the alpha
blending at the end, and is about 3x faster)
The basic operations with 32 bpp are as follows:
// Immediate conversion to 32 bpp
Pix *pixt1 = pixConvertTo32(pixs);
// Do vertical shear
Pix *pixr = pixQuadraticVerticalShear(pixt1, L_WARP_TO_RIGHT,
ybendt, ybendb,
L_BRING_IN_WHITE);
// Colorize two versions, toward red and cyan
Pix *pixc = pixCopy(NULL, pixr);
l_int32 thresh = 150; // if higher, get less original color
pixColorGray(pixr, NULL, L_PAINT_DARK, thresh, 255, 0, 0);
pixColorGray(pixc, NULL, L_PAINT_DARK, thresh, 0, 255, 255);
// Shift the red pixels; e.g., by stretching
Pix *pixrs = pixStretchHorizontal(pixr, L_WARP_TO_RIGHT,
L_QUADRATIC_WARP, zbend,
L_INTERPOLATED,
L_BRING_IN_WHITE);
// Blend the shifted red and unshifted cyan 50:50
Pix *pixg = pixCreate(w, h, 8);
pixSetAllArbitrary(pixg, 128);
pixd = pixBlendWithGrayMask(pixrs, pixc, pixg, 0, 0);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.