@swnb/dct

> dct algorithm implement in typescript

for example

luma image before dct

!luma

after dct, you can use idct to recovery origin image

!dct

install

use pnpm

``shell
pnpm i @swnb/dct
`

use npm

`shell
npm i @swnb/dct
`

usage

prepare example data

`typescript
const example = [
[65, 76, 82, 66, 18, 32],
[12, 87, 9, 2, 54, 78],
[74, 45, 18, 48, 60, 72],
[65, 2, 54, 404, 800, 905],
]
`

discrete cosine transform

`typescript
import { dct } from '@swnb/dct'

const result = dct(example)

console.log(result)
// [
// [
// 638.5003262854817, -416.9193200063309, 154.99999999999983, 42.4578222082416, -43.01259505462728,
// -17.244243642209376,
// ],
// [
// -512.6170218697843, 578.6135814300578, -184.03403633138637, -109.98075816639899,
// 29.645534009728465, -12.201804240974509,
// ],
// [
// 410.2895319161823, -385.13955429855645, 75.4999999999998, 66.54447134560958, 8.660254037844224,
// 12.49428061324591,
// ],
// [
// -188.89844420398651, 249.46420106733234, -75.84671035435811, 2.2508146252807193,
// 52.71203828296457, 1.9283180367658657,
// ],
// ]
`

inverse discrete cosine transform

`typescript
import { idct } from '@swnb/dct'

const result = dct(example)

const originData = idct(result)

console.log(originData)
// [
// [
// 64.99999999999993,
// 75.99999999999999,
// 81.99999999999997,
// 65.99999999999996,
// 17.999999999999897,
// 31.999999999999893
// ],
// [
// 11.99999999999998,
// 87.00000000000003,
// 8.999999999999943,
// 1.9999999999999762,
// 53.99999999999998,
// 78.00000000000009
// ],
// [
// 73.99999999999994,
// 45.000000000000036,
// 17.999999999999922,
// 47.99999999999986,
// 59.99999999999982,
// 71.99999999999982
// ],
// [
// 64.99999999999974,
// 2.00000000000048,
// 53.99999999999999,
// 404.0000000000001,
// 799.9999999999999,
// 904.9999999999995
// ]
// ]
`

use interface

`typescript
// if you implement Matrix or MatrixPromise

interface Matrix {
getValue: (x: number, y: number) => number
}

interface MatrixPromise {
getValue: (x: number, y: number) => Promise
}

`

you can use dctMatrix, dctMatrixPromise, idctMatrix, idctMatrixPromise to process matrix

`typescript
import { dctMatrix, idctMatrix, dctMatrixPromise, idctMatrixPromise, Matrix, MatrixPromise } from '@swnb/dct'

declare const m: number // matrix's width
declare const n: number // matrix's height
declare const matrix: Matrix // matrix implement { getValue: ( x, y ) => number } 0 <= x < m , 0 <= y < n

declare const matrixPromise: MatrixPromise

const result1 = dctMatrix(matrix, m, n)

const result2 = await dctMatrixPromise(matrixPromise, m, n)
``