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Switch from custom trim op to vips_find_trim #914

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Lovell Fuller
2018-10-02 11:24:32 +01:00
parent 11900945eb
commit 21fbe546b8
8 changed files with 34 additions and 65 deletions
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60
src/operations.cc
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@@ -324,55 +324,21 @@ namespace sharp {
return image.boolean(imageR, boolean);
}
VImage Trim(VImage image, int const tolerance) {
using sharp::MaximumImageAlpha;
// An equivalent of ImageMagick's -trim in C++ ... automatically remove
// "boring" image edges.
// We use .project to sum the rows and columns of a 0/255 mask image, the first
// non-zero row or column is the object edge. We make the mask image with an
// amount-different-from-background image plus a threshold.
// find the value of the pixel at (0, 0) ... we will search for all pixels
// significantly different from this
std::vector<double> background = image(0, 0);
double const max = MaximumImageAlpha(image.interpretation());
// we need to smooth the image, subtract the background from every pixel, take
// the absolute value of the difference, then threshold
VImage mask = (image.median(3) - background).abs() > (max * tolerance / 100);
// sum mask rows and columns, then search for the first non-zero sum in each
// direction
VImage rows;
VImage columns = mask.project(&rows);
VImage profileLeftV;
VImage profileLeftH = columns.profile(&profileLeftV);
VImage profileRightV;
VImage profileRightH = columns.fliphor().profile(&profileRightV);
VImage profileTopV;
VImage profileTopH = rows.profile(&profileTopV);
VImage profileBottomV;
VImage profileBottomH = rows.flipver().profile(&profileBottomV);
int left = static_cast<int>(floor(profileLeftV.min()));
int right = columns.width() - static_cast<int>(floor(profileRightV.min()));
int top = static_cast<int>(floor(profileTopH.min()));
int bottom = rows.height() - static_cast<int>(floor(profileBottomH.min()));
int width = right - left;
int height = bottom - top;
if (width <= 0 || height <= 0) {
/*
Trim an image
*/
VImage Trim(VImage image, int const threshold) {
// Top-left pixel provides the background colour
VImage background = image.extract_area(0, 0, 1, 1);
if (HasAlpha(background)) {
background = background.flatten();
}
int top, width, height;
int const left = image.find_trim(&top, &width, &height,
VImage::option()->set("background", background(0, 0)));
if (width == 0 || height == 0) {
throw VError("Unexpected error while trimming. Try to lower the tolerance");
}
// and now crop the original image
return image.extract_area(left, top, width, height);
}