58 lines
1004 B
JavaScript
58 lines
1004 B
JavaScript
/**
|
|
* https://en.wikipedia.org/wiki/YCbCr#JPEG_conversion
|
|
*
|
|
* JPEG conversion without head/footroom
|
|
*
|
|
* @module color-space/jpeg
|
|
*/
|
|
import rgb from './rgb.js';
|
|
|
|
|
|
var jpeg = {
|
|
name: 'jpeg',
|
|
min: [0, 0, 0],
|
|
max: [255, 255, 255],
|
|
channel: ['Y', 'Cb', 'Cr'],
|
|
alias: ['JPEG']
|
|
};
|
|
|
|
export default (jpeg);
|
|
|
|
|
|
/**
|
|
* JPEG to RGB
|
|
* transform through analog form
|
|
*
|
|
* @param {Array<number>} arr RGB values
|
|
*
|
|
* @return {Array<number>} JPEG values
|
|
*/
|
|
jpeg.rgb = function (arr) {
|
|
var y = arr[0], cb = arr[1], cr = arr[2];
|
|
|
|
return [
|
|
y + 1.402 * (cr - 128),
|
|
y - 0.34414 * (cb - 128) - 0.71414 * (cr - 128),
|
|
y + 1.772 * (cb - 128)
|
|
]
|
|
};
|
|
|
|
|
|
/**
|
|
* RGB to JPEG
|
|
* transform through analog form
|
|
*
|
|
* @param {Array<number>} arr JPEG values
|
|
*
|
|
* @return {Array<number>} RGB values
|
|
*/
|
|
rgb.jpeg = function (arr) {
|
|
var r = arr[0], g = arr[1], b = arr[2];
|
|
|
|
return [
|
|
0.299 * r + 0.587 * g + 0.114 * b,
|
|
128 - 0.168736 * r - 0.331264 * g + 0.5 * b,
|
|
128 + 0.5 * r - 0.418688 * g - 0.081312 * b
|
|
]
|
|
};
|