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1a3f26fb5c* media: add webp support Signed-off-by: Sigrid Solveig Haflínudóttir <sigrid@ftrv.se> * bump exif-terminator to v0.5.0 Signed-off-by: Sigrid Solveig Haflínudóttir <sigrid@ftrv.se> Signed-off-by: Sigrid Solveig Haflínudóttir <sigrid@ftrv.se>
98 lines
2.8 KiB
Go
98 lines
2.8 KiB
Go
// Copyright 2011 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package vp8
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// This file implements the inverse Discrete Cosine Transform and the inverse
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// Walsh Hadamard Transform (WHT), as specified in sections 14.3 and 14.4.
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func clip8(i int32) uint8 {
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if i < 0 {
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return 0
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}
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if i > 255 {
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return 255
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}
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return uint8(i)
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}
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func (z *Decoder) inverseDCT4(y, x, coeffBase int) {
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const (
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c1 = 85627 // 65536 * cos(pi/8) * sqrt(2).
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c2 = 35468 // 65536 * sin(pi/8) * sqrt(2).
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)
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var m [4][4]int32
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for i := 0; i < 4; i++ {
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a := int32(z.coeff[coeffBase+0]) + int32(z.coeff[coeffBase+8])
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b := int32(z.coeff[coeffBase+0]) - int32(z.coeff[coeffBase+8])
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c := (int32(z.coeff[coeffBase+4])*c2)>>16 - (int32(z.coeff[coeffBase+12])*c1)>>16
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d := (int32(z.coeff[coeffBase+4])*c1)>>16 + (int32(z.coeff[coeffBase+12])*c2)>>16
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m[i][0] = a + d
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m[i][1] = b + c
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m[i][2] = b - c
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m[i][3] = a - d
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coeffBase++
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}
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for j := 0; j < 4; j++ {
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dc := m[0][j] + 4
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a := dc + m[2][j]
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b := dc - m[2][j]
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c := (m[1][j]*c2)>>16 - (m[3][j]*c1)>>16
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d := (m[1][j]*c1)>>16 + (m[3][j]*c2)>>16
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z.ybr[y+j][x+0] = clip8(int32(z.ybr[y+j][x+0]) + (a+d)>>3)
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z.ybr[y+j][x+1] = clip8(int32(z.ybr[y+j][x+1]) + (b+c)>>3)
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z.ybr[y+j][x+2] = clip8(int32(z.ybr[y+j][x+2]) + (b-c)>>3)
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z.ybr[y+j][x+3] = clip8(int32(z.ybr[y+j][x+3]) + (a-d)>>3)
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}
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}
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func (z *Decoder) inverseDCT4DCOnly(y, x, coeffBase int) {
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dc := (int32(z.coeff[coeffBase+0]) + 4) >> 3
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for j := 0; j < 4; j++ {
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for i := 0; i < 4; i++ {
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z.ybr[y+j][x+i] = clip8(int32(z.ybr[y+j][x+i]) + dc)
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}
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}
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}
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func (z *Decoder) inverseDCT8(y, x, coeffBase int) {
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z.inverseDCT4(y+0, x+0, coeffBase+0*16)
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z.inverseDCT4(y+0, x+4, coeffBase+1*16)
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z.inverseDCT4(y+4, x+0, coeffBase+2*16)
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z.inverseDCT4(y+4, x+4, coeffBase+3*16)
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}
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func (z *Decoder) inverseDCT8DCOnly(y, x, coeffBase int) {
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z.inverseDCT4DCOnly(y+0, x+0, coeffBase+0*16)
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z.inverseDCT4DCOnly(y+0, x+4, coeffBase+1*16)
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z.inverseDCT4DCOnly(y+4, x+0, coeffBase+2*16)
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z.inverseDCT4DCOnly(y+4, x+4, coeffBase+3*16)
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}
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func (d *Decoder) inverseWHT16() {
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var m [16]int32
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for i := 0; i < 4; i++ {
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a0 := int32(d.coeff[384+0+i]) + int32(d.coeff[384+12+i])
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a1 := int32(d.coeff[384+4+i]) + int32(d.coeff[384+8+i])
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a2 := int32(d.coeff[384+4+i]) - int32(d.coeff[384+8+i])
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a3 := int32(d.coeff[384+0+i]) - int32(d.coeff[384+12+i])
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m[0+i] = a0 + a1
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m[8+i] = a0 - a1
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m[4+i] = a3 + a2
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m[12+i] = a3 - a2
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}
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out := 0
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for i := 0; i < 4; i++ {
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dc := m[0+i*4] + 3
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a0 := dc + m[3+i*4]
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a1 := m[1+i*4] + m[2+i*4]
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a2 := m[1+i*4] - m[2+i*4]
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a3 := dc - m[3+i*4]
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d.coeff[out+0] = int16((a0 + a1) >> 3)
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d.coeff[out+16] = int16((a3 + a2) >> 3)
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d.coeff[out+32] = int16((a0 - a1) >> 3)
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d.coeff[out+48] = int16((a3 - a2) >> 3)
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out += 64
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}
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}
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