go/src/image/jpeg/dct_test.go

func benchmarkDCT(b *testing.B, f func(*block)) { … }

func BenchmarkFDCT(b *testing.B) { … }

func BenchmarkIDCT(b *testing.B) { … }

func TestDCT(t *testing.T) { … }

// differ reports whether any pair-wise elements in b0 and b1 differ by 2 or
// more. That tolerance is because there isn't a single definitive decoding of
// a given JPEG image, even before the YCbCr to RGB conversion; implementations
// can have different IDCT rounding errors.
func differ(b0, b1 *block) bool { … }

// alpha returns 1 if i is 0 and returns √2 otherwise.
func alpha(i int) float64 { … }

var cosines …

func init() { … }

// slowFDCT performs the 8*8 2-dimensional forward discrete cosine transform:
//
//	dst[u,v] = (1/8) * Σ_x Σ_y alpha(u) * alpha(v) * src[x,y] *
//		cos((π/2) * (2*x + 1) * u / 8) *
//		cos((π/2) * (2*y + 1) * v / 8)
//
// x and y are in pixel space, and u and v are in transform space.
//
// b acts as both dst and src.
func slowFDCT(b *block) { … }

// slowIDCT performs the 8*8 2-dimensional inverse discrete cosine transform:
//
//	dst[x,y] = (1/8) * Σ_u Σ_v alpha(u) * alpha(v) * src[u,v] *
//		cos((π/2) * (2*x + 1) * u / 8) *
//		cos((π/2) * (2*y + 1) * v / 8)
//
// x and y are in pixel space, and u and v are in transform space.
//
// b acts as both dst and src.
func slowIDCT(b *block) { … }

func (b *block) String() string { … }

var testBlocks …