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Add experimental sharpness calc to stats #2251

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Lovell Fuller 2020-06-12 11:25:57 +01:00
parent 9431029917
commit 8f5495a446
6 changed files with 49 additions and 2 deletions
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5
docs/api-input.md
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@ -71,6 +71,7 @@ A `Promise` is returned when `callback` is not provided.
- `maxY` (y-coordinate of one of the pixel where the maximum lies)
- `isOpaque`: Is the image fully opaque? Will be `true` if the image has no alpha channel or if every pixel is fully opaque.
- `entropy`: Histogram-based estimation of greyscale entropy, discarding alpha channel if any (experimental)
- `sharpness`: Estimation of greyscale sharpness based on the standard deviation of a Laplacian convolution, discarding alpha channel if any (experimental)
### Parameters
@ -87,6 +88,10 @@ image
});
```
```javascript
const { entropy, sharpness } = await sharp(input).stats();
```
Returns **[Promise][5]<[Object][6]>**
[1]: https://libvips.github.io/libvips/API/current/VipsImage.html#VipsInterpretation

3
docs/changelog.md
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@ -21,6 +21,9 @@ Requires libvips v8.9.1
* Add support for named `alpha` channel to `extractChannel` operation.
[#2138](https://github.com/lovell/sharp/issues/2138)
* Add experimental `sharpness` calculation to `stats()` response.
[#2251](https://github.com/lovell/sharp/issues/2251)
### v0.25.3 - 17th May 2020
* Ensure libvips is initialised only once, improves worker thread safety.

4
lib/input.js
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@ -299,6 +299,7 @@ function metadata (callback) {
* - `maxY` (y-coordinate of one of the pixel where the maximum lies)
* - `isOpaque`: Is the image fully opaque? Will be `true` if the image has no alpha channel or if every pixel is fully opaque.
* - `entropy`: Histogram-based estimation of greyscale entropy, discarding alpha channel if any (experimental)
* - `sharpness`: Estimation of greyscale sharpness based on the standard deviation of a Laplacian convolution, discarding alpha channel if any (experimental)
*
* @example
* const image = sharp(inputJpg);
@ -308,6 +309,9 @@ function metadata (callback) {
* // stats contains the channel-wise statistics array and the isOpaque value
* });
*
* @example
* const { entropy, sharpness } = await sharp(input).stats();
*
* @param {Function} [callback] - called with the arguments `(err, stats)`
* @returns {Promise<Object>}
*/

12
src/stats.cc
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@ -75,8 +75,17 @@ class StatsWorker : public Napi::AsyncWorker {
baton->isOpaque = false;
}
}
// Convert to greyscale
vips::VImage greyscale = image.colourspace(VIPS_INTERPRETATION_B_W)[0];
// Estimate entropy via histogram of greyscale value frequency
baton->entropy = std::abs(image.colourspace(VIPS_INTERPRETATION_B_W)[0].hist_find().hist_entropy());
baton->entropy = std::abs(greyscale.hist_find().hist_entropy());
// Estimate sharpness via standard deviation of greyscale laplacian
VImage laplacian = VImage::new_matrixv(3, 3,
0.0, 1.0, 0.0,
1.0, -4.0, 1.0,
0.0, 1.0, 0.0);
laplacian.set("scale", 9.0);
baton->sharpness = greyscale.conv(laplacian).deviate();
} catch (vips::VError const &err) {
(baton->err).append(err.what());
}
@ -123,6 +132,7 @@ class StatsWorker : public Napi::AsyncWorker {
info.Set("channels", channels);
info.Set("isOpaque", baton->isOpaque);
info.Set("entropy", baton->entropy);
info.Set("sharpness", baton->sharpness);
Callback().MakeCallback(Receiver().Value(), { env.Null(), info });
} else {
Callback().MakeCallback(Receiver().Value(), { Napi::Error::New(env, baton->err).Value() });

4
src/stats.h
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@ -47,13 +47,15 @@ struct StatsBaton {
std::vector<ChannelStats> channelStats;
bool isOpaque;
double entropy;
double sharpness;
std::string err;
StatsBaton():
input(nullptr),
isOpaque(true),
entropy(0.0)
entropy(0.0),
sharpness(0.0)
{}
};

23
test/unit/stats.js
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@ -25,6 +25,7 @@ describe('Image Stats', function () {
assert.strictEqual(true, stats.isOpaque);
assert.strictEqual(true, isInAcceptableRange(stats.entropy, 7.319914765248541));
assert.strictEqual(true, isInAcceptableRange(stats.sharpness, 0.7883011147075762));
// red channel
assert.strictEqual(0, stats.channels[0].min);
@ -84,6 +85,7 @@ describe('Image Stats', function () {
assert.strictEqual(true, stats.isOpaque);
assert.strictEqual(true, isInAcceptableRange(stats.entropy, 0.3409031108021736));
assert.strictEqual(true, isInAcceptableRange(stats.sharpness, 9.111356137722868));
// red channel
assert.strictEqual(0, stats.channels[0].min);
@ -110,6 +112,7 @@ describe('Image Stats', function () {
assert.strictEqual(false, stats.isOpaque);
assert.strictEqual(true, isInAcceptableRange(stats.entropy, 0.06778064835816622));
assert.strictEqual(true, isInAcceptableRange(stats.sharpness, 2.522916068931278));
// red channel
assert.strictEqual(0, stats.channels[0].min);
@ -185,6 +188,7 @@ describe('Image Stats', function () {
assert.strictEqual(false, stats.isOpaque);
assert.strictEqual(true, isInAcceptableRange(stats.entropy, 0));
assert.strictEqual(true, isInAcceptableRange(stats.sharpness, 0));
// alpha channel
assert.strictEqual(0, stats.channels[3].min);
@ -212,6 +216,7 @@ describe('Image Stats', function () {
assert.strictEqual(true, stats.isOpaque);
assert.strictEqual(true, isInAcceptableRange(stats.entropy, 0.3851250782608986));
assert.strictEqual(true, isInAcceptableRange(stats.sharpness, 10.312521863719589));
// red channel
assert.strictEqual(0, stats.channels[0].min);
@ -239,6 +244,7 @@ describe('Image Stats', function () {
assert.strictEqual(true, stats.isOpaque);
assert.strictEqual(true, isInAcceptableRange(stats.entropy, 7.51758075132966));
assert.strictEqual(true, isInAcceptableRange(stats.sharpness, 9.959951636662941));
// red channel
assert.strictEqual(0, stats.channels[0].min);
@ -298,6 +304,7 @@ describe('Image Stats', function () {
assert.strictEqual(true, stats.isOpaque);
assert.strictEqual(true, isInAcceptableRange(stats.entropy, 6.087309412541799));
assert.strictEqual(true, isInAcceptableRange(stats.sharpness, 2.9250574456255682));
// red channel
assert.strictEqual(35, stats.channels[0].min);
@ -357,6 +364,7 @@ describe('Image Stats', function () {
assert.strictEqual(false, stats.isOpaque);
assert.strictEqual(true, isInAcceptableRange(stats.entropy, 1));
assert.strictEqual(true, isInAcceptableRange(stats.sharpness, 15.870619016486861));
// gray channel
assert.strictEqual(0, stats.channels[0].min);
@ -410,6 +418,7 @@ describe('Image Stats', function () {
assert.strictEqual(true, stats.isOpaque);
assert.strictEqual(true, isInAcceptableRange(stats.entropy, 7.319914765248541));
assert.strictEqual(true, isInAcceptableRange(stats.sharpness, 0.788301114707569));
// red channel
assert.strictEqual(0, stats.channels[0].min);
@ -472,6 +481,7 @@ describe('Image Stats', function () {
return pipeline.stats().then(function (stats) {
assert.strictEqual(true, stats.isOpaque);
assert.strictEqual(true, isInAcceptableRange(stats.entropy, 7.319914765248541));
assert.strictEqual(true, isInAcceptableRange(stats.sharpness, 0.788301114707569));
// red channel
assert.strictEqual(0, stats.channels[0].min);
@ -529,6 +539,7 @@ describe('Image Stats', function () {
return sharp(fixtures.inputJpg).stats().then(function (stats) {
assert.strictEqual(true, stats.isOpaque);
assert.strictEqual(true, isInAcceptableRange(stats.entropy, 7.319914765248541));
assert.strictEqual(true, isInAcceptableRange(stats.sharpness, 0.788301114707569));
// red channel
assert.strictEqual(0, stats.channels[0].min);
@ -582,6 +593,18 @@ describe('Image Stats', function () {
});
});
it('Blurred image has lower sharpness than original', () => {
const original = sharp(fixtures.inputJpg).stats();
const blurred = sharp(fixtures.inputJpg).blur().toBuffer().then(blur => sharp(blur).stats());
return Promise
.all([original, blurred])
.then(([original, blurred]) => {
assert.strictEqual(true, isInAcceptableRange(original.sharpness, 0.7883011147075476));
assert.strictEqual(true, isInAcceptableRange(blurred.sharpness, 0.4791559805997398));
});
});
it('File input with corrupt header fails gracefully', function (done) {
sharp(fixtures.inputJpgWithCorruptHeader)
.stats(function (err) {