NAME
Image::Leptonica::Func::dewarp2
VERSION
version 0.04
dewarp2.c
dewarp2.c
Build the page disparity model
Build page disparity model
l_int32 dewarpBuildPageModel()
l_int32 dewarpFindVertDisparity()
l_int32 dewarpFindHorizDisparity()
PTAA *dewarpGetTextlineCenters()
static PTA *dewarpGetMeanVerticals()
PTAA *dewarpRemoveShortLines()
static l_int32 dewarpGetLineEndpoints()
static l_int32 dewarpQuadraticLSF()
Build the line disparity model
l_int32 dewarpBuildLineModel()
Query model status
l_int32 dewarpaModelStatus()
Rendering helpers
static l_int32 pixRenderFlats()
static l_int32 pixRenderHorizEndPointsFUNCTIONS
dewarpBuildLineModel
l_int32 dewarpBuildLineModel ( L_DEWARP *dew, l_int32 opensize, const char *debugfile )
dewarpBuildLineModel()
Input: dew
opensize (size of opening to remove perpendicular lines)
debugfile (use null to skip writing this)
Return: 0 if OK, 1 if unable to build the model or on error
Notes:
(1) This builds the horizontal and vertical disparity arrays
for an input of ruled lines, typically for calibration.
In book scanning, you could lay the ruled paper over a page.
Then for that page and several below it, you can use the
disparity correction of the line model to dewarp the pages.
(2) The dew has been initialized with the image of ruled lines.
These lines must be continuous, but we do a small amount
of pre-processing here to insure that.
(3) @opensize is typically about 8. It must be larger than
the thickness of the lines to be extracted. This is the
default value, which is applied if @opensize < 3.
(4) Sets vsuccess = 1 and hsuccess = 1 if the vertical and/or
horizontal disparity arrays build.
(5) Similar to dewarpBuildPageModel(), except here the vertical
and horizontal disparity arrays are both built from ruled lines.
See notes there.dewarpBuildPageModel
l_int32 dewarpBuildPageModel ( L_DEWARP *dew, const char *debugfile )
dewarpBuildPageModel()
Input: dew
debugfile (use null to skip writing this)
Return: 0 if OK, 1 if unable to build the model or on error
Notes:
(1) This is the basic function that builds the horizontal and
vertical disparity arrays, which allow determination of the
src pixel in the input image corresponding to each
dest pixel in the dewarped image.
(2) Sets vsuccess = 1 if the vertical disparity array builds.
Always attempts to build the horizontal disparity array,
even if it will not be requested (useboth == 0).
Sets hsuccess = 1 if horizontal disparity builds.
(3) The method is as follows:
(a) Estimate the points along the centers of all the
long textlines. If there are too few lines, no
disparity models are built.
(b) From the vertical deviation of the lines, estimate
the vertical disparity.
(c) From the ends of the lines, estimate the horizontal
disparity, assuming that the text is made of lines
that are left and right justified.
(d) One can also compute an additional contribution to the
horizontal disparity, inferred from slopes of the top
and bottom lines. We do not do this.
(4) In more detail for the vertical disparity:
(a) Fit a LS quadratic to center locations along each line.
This smooths the curves.
(b) Sample each curve at a regular interval, find the y-value
of the mid-point on each curve, and subtract the sampled
curve value from this value. This is the vertical
disparity at sampled points along each curve.
(c) Fit a LS quadratic to each set of vertically aligned
disparity samples. This smooths the disparity values
in the vertical direction. Then resample at the same
regular interval. We now have a regular grid of smoothed
vertical disparity valuels.
(5) Once the sampled vertical disparity array is found, it can be
interpolated to get a full resolution vertical disparity map.
This can be applied directly to the src image pixels
to dewarp the image in the vertical direction, making
all textlines horizontal. Likewise, the horizontal
disparity array is used to left- and right-align the
longest textlines.dewarpFindHorizDisparity
l_int32 dewarpFindHorizDisparity ( L_DEWARP *dew, PTAA *ptaa )
dewarpFindHorizDisparity()
Input: dew
ptaa (unsmoothed lines, not vertically ordered)
Return: 0 if OK, 1 if vertical disparity array is no built or on error
(1) This is not required for a successful model; only the vertical
disparity is required. This will not be called if the
function to build the vertical disparity fails.
(2) Debug output goes to /tmp/dewmod/ for collection into a pdf.dewarpFindVertDisparity
l_int32 dewarpFindVertDisparity ( L_DEWARP *dew, PTAA *ptaa, l_int32 rotflag )
dewarpFindVertDisparity()
Input: dew
ptaa (unsmoothed lines, not vertically ordered)
rotflag (0 if using dew->pixs; 1 if rotated by 90 degrees cw)
Return: 0 if OK, 1 on error
Notes:
(1) This starts with points along the centers of textlines.
It does quadratic fitting (and smoothing), first along the
lines and then in the vertical direction, to generate
the sampled vertical disparity map. This can then be
interpolated to full resolution and used to remove
the vertical line warping.
(2) Use @rotflag == 1 if you are dewarping vertical lines, as
is done in dewarpBuildLineModel(). The usual case is for
@rotflag == 0.
(3) The model fails to build if the vertical disparity fails.
This sets the vsuccess flag to 1 on success.
(4) Pix debug output goes to /tmp/dewvert/ for collection into
a pdf. Non-pix debug output goes to /tmp.dewarpGetTextlineCenters
PTAA * dewarpGetTextlineCenters ( PIX *pixs, l_int32 debugflag )
dewarpGetTextlineCenters()
Input: pixs (1 bpp)
debugflag (1 for debug output)
Return: ptaa (of center values of textlines)
Notes:
(1) This in general does not have a point for each value
of x, because there will be gaps between words.
It doesn't matter because we will fit a quadratic to the
points that we do have.dewarpRemoveShortLines
PTAA * dewarpRemoveShortLines ( PIX *pixs, PTAA *ptaas, l_float32 fract, l_int32 debugflag )
dewarpRemoveShortLines()
Input: pixs (1 bpp)
ptaas (input lines)
fract (minimum fraction of longest line to keep)
debugflag
Return: ptaad (containing only lines of sufficient length),
or null on errordewarpaModelStatus
l_int32 dewarpaModelStatus ( L_DEWARPA *dewa, l_int32 pageno, l_int32 *pvsuccess, l_int32 *phsuccess )
dewarpaModelStatus()
Input: dewa
pageno
&vsuccess (<optional return> 1 on success)
&hsuccess (<optional return> 1 on success)
Return: 0 if OK, 1 on error
Notes:
(1) This tests if a model has been built, not if it is valid.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.