--- /dev/null
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package image
+
+// TODO(nigeltao): Clarify semantics wrt premultiplied vs unpremultiplied colors.
+// It's probably also worth thinking about floating-point color models.
+
+// All Colors can convert themselves, with a possible loss of precision, to 128-bit RGBA.
+type Color interface {
+ RGBA() (r, g, b, a uint32);
+}
+
+// An RGBAColor represents a traditional 32-bit color, having 8 bits for each of red, green, blue and alpha.
+type RGBAColor struct {
+ R, G, B, A uint8;
+}
+
+func (c RGBAColor) RGBA() (r, g, b, a uint32) {
+ r = uint32(c.R);
+ r |= r<<8;
+ r |= r<<16;
+ g = uint32(c.G);
+ g |= g<<8;
+ g |= g<<16;
+ b = uint32(c.B);
+ b |= b<<8;
+ b |= b<<16;
+ a = uint32(c.A);
+ a |= a<<8;
+ a |= a<<16;
+ return;
+}
+
+// An RGBA64Color represents a 64-bit color, having 16 bits for each of red, green, blue and alpha.
+type RGBA64Color struct {
+ R, G, B, A uint16;
+}
+
+func (c RGBA64Color) RGBA() (r, g, b, a uint32) {
+ r = uint32(c.R);
+ r |= r<<16;
+ g = uint32(c.G);
+ g |= g<<16;
+ b = uint32(c.B);
+ b |= b<<16;
+ a = uint32(c.A);
+ a |= a<<16;
+ return;
+}
+
+// A ColorModel can convert foreign Colors, with a possible loss of precision, to a Color
+// from its own color model.
+type ColorModel interface {
+ Convert(c Color) Color;
+}
+
+// The ColorModelFunc type is an adapter to allow the use of an ordinary
+// color conversion function as a ColorModel. If f is such a function,
+// ColorModelFunc(f) is a ColorModel object that invokes f to implement
+// the conversion.
+type ColorModelFunc func(Color) Color
+
+func (f ColorModelFunc) Convert(c Color) Color {
+ return f(c);
+}
+
+func toRGBAColor(c Color) Color {
+ if _, ok := c.(RGBAColor); ok { // no-op conversion
+ return c;
+ }
+ r, g, b, a := c.RGBA();
+ return RGBAColor{ uint8(r>>24), uint8(g>>24), uint8(b>>24), uint8(a>>24) };
+}
+
+func toRGBA64Color(c Color) Color {
+ if _, ok := c.(RGBA64Color); ok { // no-op conversion
+ return c;
+ }
+ r, g, b, a := c.RGBA();
+ return RGBA64Color{ uint16(r>>16), uint16(g>>16), uint16(b>>16), uint16(a>>16) };
+}
+
+// The ColorModel associated with RGBAColor.
+var RGBAColorModel ColorModel = ColorModelFunc(toRGBAColor);
+
+// The ColorModel associated with RGBA64Color.
+var RGBA64ColorModel ColorModel = ColorModelFunc(toRGBA64Color);
+
--- /dev/null
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// The image package implements a basic 2-D image library.
+package image
+
+// An Image is a rectangular grid of Colors drawn from a ColorModel.
+type Image interface {
+ ColorModel() ColorModel;
+ Width() int;
+ Height() int;
+ // At(0, 0) returns the upper-left pixel of the grid.
+ // At(Width()-1, Height()-1) returns the lower-right pixel.
+ At(x, y int) Color;
+}
+
+// An RGBA is an in-memory image backed by a 2-D slice of RGBAColor values.
+type RGBA struct {
+ // The Pixel field's indices are y first, then x, so that At(x, y) == Pixel[y][x].
+ Pixel [][]RGBAColor;
+}
+
+func (p *RGBA) ColorModel() ColorModel {
+ return RGBAColorModel;
+}
+
+func (p *RGBA) Width() int {
+ if len(p.Pixel) == 0 {
+ return 0;
+ }
+ return len(p.Pixel[0]);
+}
+
+func (p *RGBA) Height() int {
+ return len(p.Pixel);
+}
+
+func (p *RGBA) At(x, y int) Color {
+ return p.Pixel[y][x];
+}
+
+func (p *RGBA) Set(x, y int, c Color) {
+ p.Pixel[y][x] = toRGBAColor(c).(RGBAColor);
+}
+
+// An RGBA64 is an in-memory image backed by a 2-D slice of RGBA64Color values.
+type RGBA64 struct {
+ // The Pixel field's indices are y first, then x, so that At(x, y) == Pixel[y][x].
+ Pixel [][]RGBA64Color;
+}
+
+func (p *RGBA64) ColorModel() ColorModel {
+ return RGBA64ColorModel;
+}
+
+func (p *RGBA64) Width() int {
+ if len(p.Pixel) == 0 {
+ return 0;
+ }
+ return len(p.Pixel[0]);
+}
+
+func (p *RGBA64) Height() int {
+ return len(p.Pixel);
+}
+
+func (p *RGBA64) At(x, y int) Color {
+ return p.Pixel[y][x];
+}
+
+func (p *RGBA64) Set(x, y int, c Color) {
+ p.Pixel[y][x] = toRGBA64Color(c).(RGBA64Color);
+}
+
+// A PalettedColorModel represents a fixed palette of colors.
+type PalettedColorModel []Color;
+
+func diff(a, b uint32) uint32 {
+ if a > b {
+ return a - b;
+ }
+ return b - a;
+}
+
+// Convert returns the palette color closest to c in Euclidean R,G,B space.
+func (p PalettedColorModel) Convert(c Color) Color {
+ if len(p) == 0 {
+ return nil;
+ }
+ // TODO(nigeltao): Revisit the "pick the palette color which minimizes sum-squared-difference"
+ // algorithm when the premultiplied vs unpremultiplied issue is resolved.
+ // Currently, we only compare the R, G and B values, and ignore A.
+ cr, cg, cb, ca := c.RGBA();
+ // Shift by 17 bits to avoid potential uint32 overflow in sum-squared-difference.
+ cr >>= 17;
+ cg >>= 17;
+ cb >>= 17;
+ result := Color(nil);
+ bestSSD := uint32(1<<32 - 1);
+ for _, v := range p {
+ vr, vg, vb, va := v.RGBA();
+ vr >>= 17;
+ vg >>= 17;
+ vb >>= 17;
+ dr, dg, db := diff(cr, vr), diff(cg, vg), diff(cb, vb);
+ ssd := (dr * dr) + (dg * dg) + (db * db);
+ if ssd < bestSSD {
+ bestSSD = ssd;
+ result = v;
+ }
+ }
+ return result;
+}
+
+// A Paletted is an in-memory image backed by a 2-D slice of byte values and a PalettedColorModel.
+type Paletted struct {
+ // The Pixel field's indices are y first, then x, so that At(x, y) == Palette[Pixel[y][x]].
+ Pixel [][]byte;
+ Palette PalettedColorModel;
+}
+
+func (p *Paletted) ColorModel() ColorModel {
+ return p.Palette;
+}
+
+func (p *Paletted) Width() int {
+ if len(p.Pixel) == 0 {
+ return 0;
+ }
+ return len(p.Pixel[0]);
+}
+
+func (p *Paletted) Height() int {
+ return len(p.Pixel);
+}
+
+func (p *Paletted) At(x, y int) Color {
+ return p.Palette[p.Pixel[y][x]];
+}