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https://github.com/duniul/pixel-scale

📐 Get the pixel scale of an image, or scale it up or down without quality loss. Useful for pixel art!
https://github.com/duniul/pixel-scale

canvas image image-processing image-resize imagedata pixel-art pixels

Last synced: about 2 months ago
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📐 Get the pixel scale of an image, or scale it up or down without quality loss. Useful for pixel art!

Host: GitHub
URL: https://github.com/duniul/pixel-scale
Owner: duniul
License: isc
Created: 2020-09-04T20:50:04.000Z (over 4 years ago)
Default Branch: main
Last Pushed: 2024-05-13T08:01:10.000Z (7 months ago)
Last Synced: 2024-10-02T09:18:07.027Z (3 months ago)
Topics: canvas, image, image-processing, image-resize, imagedata, pixel-art, pixels
Language: TypeScript
Homepage: https://pixel-scale.netlify.app
Size: 568 KB
Stars: 19
Watchers: 1
Forks: 0
Open Issues: 0
Metadata Files:
- Readme: README.md
- Changelog: CHANGELOG.md
- License: LICENSE

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README

        










# pixel-scale

[![](https://img.shields.io/npm/v/pixel-scale?color=brightgreen)](https://www.npmjs.com/package/pixel-scale)

[![](https://img.shields.io/bundlephobia/minzip/pixel-scale)](https://bundlephobia.com/result?p=pixel-scale)

📐 Get the pixel scale of an image, or scale it up or down without quality loss. Useful for pixel

art!

- 👀 Zero loss of quality

- 🤖 Auto-detects current scale by default

- ⏫ Can scale by multiplier or to a specific scale

- 0️⃣ Zero dependencies

- 🖼️ Works directly on [ImageData](#imagedata)

## Table of contents

- [Demo](#demo)

- [Installation](#installation)

- [Usage](#usage)

  - [`scalePixels(imageData, to, options)`](#scalepixelsimagedata-to-options)

  - [`getPixelScale(imageData, options)`](#getpixelscaleimagedata-options)

  - [`multiplyPixelScale(imageData, by, options)`](#multiplypixelscaleimagedata-by-options)

  - [`dividePixelScale(imageData, by, options)`](#divideixelscaleimagedata-by-options)

- [About](#about)

  - [ImageData](#imagedata)

  - [Pixel scale](#pixel-scale-1)

  - [How does it work?](#how-does-it-work)

## Demo

https://pixel-scale.netlify.app

## Installation

| npm                       | yarn                    |

| ------------------------- | ----------------------- |

| `npm install pixel-scale` | `yarn add pixel-scale`  |

## Usage

### `scalePixels(imageData, to, options)`

Up- or downscales an image to the specified scale, without losing quality or changing any colors.

**Parameters:**

- `imageData` (ImageData instance) - The ImageData instance to scale.

- `to` (number) - The desired scale of the new image.

- `options` (object, optional)

  - `from` (number) - The current scale of the image. If no `from` value is provided, the scale is

    calculated with `getPixelScale`. Only provide a `from` value if you are sure of the current

    pixel scale and want to save time.

  - `maxColorDiff` (number, default: 0) - Passed along to `getPixelScale` if no `from` value is set,

    otherwise does nothing.

**Return value:**

A new, scaled ImageData-instance.

**Examples:**

```js

import { scalePixels } from 'pixel-scale';

// detect an image's current scale, and rescale it to 1

const scale1ImageData = scalePixels(imageData, 1);

// increase an image's scale from 5 to 10

const scale10ImageData = scalePixels(imageData, 10, { from: 5 });

// detect an image's current scale, allowing a color diff of 10,

// and rescale it to 2

const scale2ImageData = scalePixels(imageData, 2, { maxColorDiff: 10 });

```

### `getPixelScale(imageData, options)`

Get the current pixel scale of an image.

**Parameters:**

- `imageData` (ImageData instance) - The ImageData instance to scale.

- `options` (object, optional)

  - `maxColorDiff` (number, default: 0) - See `scalePixels`'s `maxColorDiff` option.

**Return value:**

A number indicating the image's pixel scale.

**Examples:**

```js

import { getPixelScale } from 'pixel-scale';

// get an image's pixel scale

const imageScale = getPixelScale(imageData);

// get an image's pixel scale, allowing a maximum difference of 10 when comparing

// color channels of individual pixels

const imageScale = getPixelScale(imageData, { maxColorDiff: 10 });

```

### `multiplyPixelScale(imageData, by, options)`

Similar to `scalePixels`, but upscales the image by the specified multiplier instead of to a specific scale. Detects the current scale of the image if no `options.from` value is provided.

**Parameters:**

- `imageData` (ImageData instance) - The ImageData instance to upscale.

- `by` (number) - The amount to multiply the image's current scale by.

- `options` (object, optional) - See `scalePixels`'s `options`.

**Return value:**

A new, scaled ImageData-instance.

**Examples:**

```js

import { multiplyPixelScale } from 'pixel-scale';

// detect an image's current scale, and double it's size

const doubledImageData = multiplyPixelScale(imageData, 2);

// take an image of scale 5, and multiply it by 10

const tenfoldImageData = multiplyPixelScale(imageData, 10, { from: 5 });

```

### `dividePixelScale(imageData, by, options)`

Similar to `scalePixels`, but downscales the image by the specified amount of times instead of to a specific scale. Detects the current scale of the image if no `options.from` value is provided.

**Parameters:**

- `imageData` (ImageData instance) - The ImageData instance to downscale.

- `by` (number) - The amount to divide the image's current scale by.

- `options` (object, optional) - See `scalePixels`'s `options`.

**Return value:**

A new, scaled ImageData-instance.

**Examples:**

```js

import { dividePixelScale } from 'pixel-scale';

// detect an image's current scale, and make it half as big

const doubledImageData = dividePixelScale(imageData, 2);

// take an image of scale 8 and divide it by 4

const tenfoldImageData = dividePixelScale(imageData, 4, { from: 8 });

```

## About

### ImageData

All functions operate on [ImageData](https://developer.mozilla.org/en-US/docs/Web/API/ImageData),

which can be retrieved from a

[canvas](https://developer.mozilla.org/en-US/docs/Web/HTML/Element/canvas) in the browser or e.g.

[node-canvas](https://github.com/Automattic/node-canvas) or [sharp](https://github.com/lovell/sharp)

on Node.

### Pixel scale

The pixel scale referred to in this readme is the amount of times a pixel of e.g. a pixel art image

has been multiplied to increase the image size. For example,

[this image](https://github.com/duniul/pixel-scale/blob/master/test/images/pixel-the-cat_x1.png) has

a pixel scale of 1, while

[this image](https://github.com/duniul/pixel-scale/blob/master/test/images/pixel-the-cat_x10.png)

has a pixel scale of 10.

### How does it work?

To get the pixel scale of an image, `pixel-scale` first figures out the common divisors of the

image's height and width. This is done using Euclid's algorithm for finding the greatest common

divisor, and then counting down. A more performant method (e.g. prime factorization/Pollard rho) is

not deemed necessary here, as image dimensions never go up to those sizes that big.

It then tests each common divisor, starting with the largest one, by chunking up the image equally

sized pieces and verifying that they each chunk is in a solid color (scaled pixels). If a chunk

contains a different color outside of the max allowed span (`maxColorDiff`), then it will go to the

next divisor. If every chunk is a solid color, then the divisor is most likely the pixel scale of

the image.