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Improve normalise op with use of histogram #200

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Lovell Fuller 2022-09-04 10:31:43 +01:00
parent 9a54a034e1
commit 55c4d8807c
3 changed files with 7 additions and 6 deletions
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3
docs/changelog.md
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@ -16,6 +16,9 @@ Requires libvips v8.13.0
* The `flip` and `flop` operations will now occur before the `rotate` operation. * The `flip` and `flop` operations will now occur before the `rotate` operation.
* Improve `normalise` operation with use of histogram.
[#200](https://github.com/lovell/sharp/issues/200)
* Use combined bounding box of alpha and non-alpha channels for `trim` operation. * Use combined bounding box of alpha and non-alpha channels for `trim` operation.
[#2166](https://github.com/lovell/sharp/issues/2166) [#2166](https://github.com/lovell/sharp/issues/2166)

7
src/operations.cc
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@ -68,10 +68,9 @@ namespace sharp {
// Extract luminance // Extract luminance
VImage luminance = lab[0]; VImage luminance = lab[0];
// Find luminance range // Find luminance range
VImage stats = luminance.stats(); int const min = luminance.percent(1);
double min = stats(0, 0)[0]; int const max = luminance.percent(99);
double max = stats(1, 0)[0]; if (std::abs(max - min) > 1) {
if (min != max) {
// Extract chroma // Extract chroma
VImage chroma = lab.extract_band(1, VImage::option()->set("n", 2)); VImage chroma = lab.extract_band(1, VImage::option()->set("n", 2));
// Calculate multiplication factor and addition // Calculate multiplication factor and addition

3
test/unit/normalize.js
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@ -13,7 +13,7 @@ const assertNormalized = function (data) {
max = Math.max(max, data[i]); max = Math.max(max, data[i]);
} }
assert.strictEqual(0, min); assert.strictEqual(0, min);
assert.strictEqual(255, max); assert.ok([254, 255].includes(max));
}; };
describe('Normalization', function () { describe('Normalization', function () {
@ -30,7 +30,6 @@ describe('Normalization', function () {
it('spreads grayscaled image values between 0 and 255', function (done) { it('spreads grayscaled image values between 0 and 255', function (done) {
sharp(fixtures.inputJpgWithLowContrast) sharp(fixtures.inputJpgWithLowContrast)
.gamma()
.greyscale() .greyscale()
.normalize(true) .normalize(true)
.raw() .raw()