LooksSame


Pure node.js library for comparing png images, taking into account human color
perception. It is created specially for the needs of visual regression testing
for testplane utility, but can be used
for other purposes.

Benchmark

Benchmark is presented in the corresponding directory.

- Benchmark description
- Benchmark results

Comparing images

``javascript
const looksSame = require('looks-same');

// equal will be true, if images looks the same
const {equal} = await looksSame('image1.png', 'image2.png');
`

Parameters can be paths to files or buffer with compressed image.

By default, it will detect only noticeable differences. If you wish to detect any difference,
use strict options:

`javascript
const {equal} = await looksSame('image1.png', 'image2.png', {strict: true});
`

You can also adjust the ΔE value that will be treated as error
in non-strict mode:

`javascript
const {equal} = await looksSame('image1.png', 'image2.png', {tolerance: 5});
`

Default tolerance in non-strict mode is 2.3 which is enough for the most cases.
Setting tolerance to 0 will produce the same result as strict: true, but strict mode
is faster.
Attempt to set tolerance in strict mode will produce an error.

Some devices can have different proportion between physical and logical screen resolutions also
known as pixel ratio. Default value for this proportion is 1.
This param also affects the comparison result, so it can be set manually with pixelRatio option.

`javascript
const {equal} = await looksSame('image1.png', 'image2.png', {pixelRatio: 2});
`

$3

Text caret in text input elements it is a pain for visual regression tasks, because it is always blinks. These diffs will be ignored by default. You can use ignoreCaret option with false value to disable ignoring such diffs. In that way text caret will be marked as diffs.

`javascript
const {equal} = await looksSame('image1.png', 'image2.png', {ignoreCaret: true});
`

Both strict and ignoreCaret can be set independently of one another.

$3

Some images has difference while comparing because of antialiasing. These diffs will be ignored by default. You can use ignoreAntialiasing option with false value to disable ignoring such diffs. In that way antialiased pixels will be marked as diffs. Read more about anti-aliasing algorithm.

`javascript
const {equal} = await looksSame('image1.png', 'image2.png', {ignoreAntialiasing: true});
`

Sometimes the antialiasing algorithm can work incorrectly due to some features of the browser rendering engine. Use the option antialiasingTolerance to make the algorithm less strict. With this option you can specify the minimum difference in brightness (zero by default) between the darkest/lightest pixel (which is adjacent to the antialiasing pixel) and theirs adjacent pixels.

We recommend that you don't increase this value above 10. If you need to increase more than 10 then this is definitely not antialiasing.

Example:
`javascript
const {equal} = await looksSame('image1.png', 'image2.png', {ignoreAntialiasing: true, antialiasingTolerance: 3});
`

$3


Looksame returns information about diff bounds. It returns only first pixel if you passed stopOnFirstFail option with true value. The whole diff area would be returned if stopOnFirstFail option is not passed or it's passed with false value.

$3

Looksame returns diff bounds divided into clusters if option shouldCluster passed with true value. Moreover you can pass clusters size using clustersSize option.

`javascript
// {
// equal: false,
// diffBounds: {left: 10, top: 10, right: 20, bottom: 20}
// diffClusters: [
// {left: 10, top: 10, right: 14, bottom: 14},
// {left: 16, top: 16, right: 20, bottom: 20}
// ]
// }
const {equal, diffBounds, diffClusters} = await looksSame('image1.png', 'image2.png', {shouldCluster: true, clustersSize: 10});
`

Building diff image

`javascript
await looksSame.createDiff({
reference: '/path/to/reference/image.png',
current: '/path/to/current/image.png',
diff: '/path/to/save/diff/to.png',
highlightColor: '#ff00ff', // color to highlight the differences
strict: false, // strict comparsion
tolerance: 2.5,
antialiasingTolerance: 0,
ignoreAntialiasing: true, // ignore antialising by default
ignoreCaret: true // ignore caret by default
});
`

Building diff image as a Buffer

If you don't want the diff image to be written on disk, then simply don't
pass any diff: path to the createDiff method. The method will then
resolve a Buffer containing the diff. You can also specify buffer format
with extension key. Default extension is png. List of supported formats:
heic, heif, avif, jpeg, jpg, png, raw, tiff, tif, webp, gif, jp2, jpx, j2k, j2c

`javascript
const buffer = await looksSame.createDiff({
// exactly same options as above, but with optional extension and without diff
extension: 'png'
});
`

Comparing images and creating diff image simultaneously

If you need both co compare images and create diff image, you can pass option createDiffImage: true,
it would work faster than two separate function calls:

`javascript
const {
equal,
diffImage,
differentPixels,
totalPixels,
diffBounds,
diffClusters
} = await looksSame('image1.png', 'image2.png', {createDiffImage: true});

if (!equal) {
await diffImage.save('diffImage.png');
}
`

Comparing colors

If you just need to compare two colors you can use colors function:

`javascript
const equal = looksSame.colors(
{R: 255, G: 0, B: 0},
{R: 254, G: 1, B: 1},
{tolerance: 2.5}
);
``