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Add normalize() for simple histogram stretching

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Available as normalize() or normalise().
Normalization takes place in LAB place and thus should not change any
colors.

Existing alpha channels are preserved untouched by normalization.
This commit is contained in:
Bernhard K. Weisshuhn
2015-04-16 19:04:33 +02:00
parent ba034a8164
commit dce36e0074
9 changed files with 240 additions and 3 deletions
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87
src/resize.cc
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@@ -83,6 +83,7 @@ struct ResizeBaton {
double sharpenJagged;
double gamma;
bool greyscale;
bool normalize;
int angle;
bool rotateBeforePreExtract;
bool flip;
@@ -115,6 +116,7 @@ struct ResizeBaton {
sharpenJagged(2.0),
gamma(0.0),
greyscale(false),
normalize(false),
angle(0),
flip(false),
flop(false),
@@ -694,6 +696,86 @@ class ResizeWorker : public NanAsyncWorker {
image = gammaDecoded;
}
// Apply normalization
if (baton->normalize) {
VipsInterpretation typeBeforeNormalize = image->Type;
if (typeBeforeNormalize == VIPS_INTERPRETATION_RGB) {
typeBeforeNormalize = VIPS_INTERPRETATION_sRGB;
}
// normalize the luminance band in LAB space:
VipsImage *lab;
if (vips_colourspace(image, &lab, VIPS_INTERPRETATION_LAB, NULL)) {
return Error();
}
vips_object_local(hook, lab);
VipsImage *luminance;
if (vips_extract_band(lab, &luminance, 0, "n", 1, NULL)) {
return Error();
}
vips_object_local(hook, luminance);
VipsImage *chroma;
if (vips_extract_band(lab, &chroma, 1, "n", 2, NULL)) {
return Error();
}
vips_object_local(hook, chroma);
VipsImage *stats;
if (vips_stats(luminance, &stats, NULL)) {
return Error();
}
vips_object_local(hook, stats);
double min = *VIPS_MATRIX(stats, 0, 0);
double max = *VIPS_MATRIX(stats, 1, 0);
VipsImage *normalized;
if (min == max) {
// Range of zero: create black image
if (vips_black(&normalized, image->Xsize, image->Ysize, "bands", 1, NULL )) {
return Error();
}
vips_object_local(hook, normalized);
} else {
double f = 100.0 / (max - min);
double a = -(min * f);
VipsImage *luminance100;
if (vips_linear1(luminance, &luminance100, f, a, NULL)) {
return Error();
}
vips_object_local(hook, luminance100);
VipsImage *normalizedLab;
if (vips_bandjoin2(luminance100, chroma, &normalizedLab, NULL)) {
return Error();
}
vips_object_local(hook, normalizedLab);
if (vips_colourspace(normalizedLab, &normalized, typeBeforeNormalize, NULL)) {
return Error();
}
vips_object_local(hook, normalized);
}
if (HasAlpha(image)) {
VipsImage *alpha;
if (vips_extract_band(image, &alpha, image->Bands - 1, "n", 1, NULL)) {
return Error();
}
vips_object_local(hook, alpha);
VipsImage *normalizedAlpha;
if (vips_bandjoin2(normalized, alpha, &normalizedAlpha, NULL)) {
return Error();
}
vips_object_local(hook, normalizedAlpha);
image = normalizedAlpha;
} else {
image = normalized;
}
}
// Convert image to sRGB, if not already
if (image->Type != VIPS_INTERPRETATION_sRGB) {
// Switch intrepretation to sRGB
@@ -762,10 +844,10 @@ class ResizeWorker : public NanAsyncWorker {
#if (VIPS_MAJOR_VERSION >= 8 || (VIPS_MAJOR_VERSION >= 7 && VIPS_MINOR_VERSION >= 42))
} else if (baton->output == "__raw") {
// Write raw, uncompressed image data to buffer
if (baton->greyscale) {
if (baton->greyscale || image->Type == VIPS_INTERPRETATION_B_W) {
// Extract first band for greyscale image
VipsImage *grey;
if (vips_extract_band(image, &grey, 1, NULL)) {
if (vips_extract_band(image, &grey, 0, NULL)) {
return Error();
}
vips_object_local(hook, grey);
@@ -1082,6 +1164,7 @@ NAN_METHOD(resize) {
baton->sharpenJagged = options->Get(NanNew<String>("sharpenJagged"))->NumberValue();
baton->gamma = options->Get(NanNew<String>("gamma"))->NumberValue();
baton->greyscale = options->Get(NanNew<String>("greyscale"))->BooleanValue();
baton->normalize = options->Get(NanNew<String>("normalize"))->BooleanValue();
baton->angle = options->Get(NanNew<String>("angle"))->Int32Value();
baton->rotateBeforePreExtract = options->Get(NanNew<String>("rotateBeforePreExtract"))->BooleanValue();
baton->flip = options->Get(NanNew<String>("flip"))->BooleanValue();