binary.go

// Copyright 2015 Google Inc. All Rights Reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package imgdiff

import (
	"image"
	"image/color"
)

type binary struct{}

// NewBinary creates a new Differ based on simple binary algorithm.
func NewBinary() Differ {
	return &binary{}
}

// Compare compares a and b using binary comparison.
func (d *binary) Compare(a, b image.Image) (image.Image, int, error) {
	ab, bb := a.Bounds(), b.Bounds()
	w, h := ab.Dx(), ab.Dy()
	if w != bb.Dx() || h != bb.Dy() {
		return nil, -1, ErrSize
	}
	diff := image.NewNRGBA(image.Rect(0, 0, w, h))
	n := 0
	for y := 0; y < h; y++ {
		for x := 0; x < w; x++ {
			d := diffColor(a.At(ab.Min.X+x, ab.Min.Y+y), b.At(bb.Min.X+x, bb.Min.Y+y))
			c := color.RGBA{0, 0, 0, 0xff}
			if d > 0 {
				c.R = 0xff
				//c.A = uint8(100 + d*0xff/0xffff)
				n++
			}
			diff.Set(x, y, c)
		}
	}
	return diff, n, nil
}

func diffColor(c1, c2 color.Color) int64 {
	r1, g1, b1, a1 := c1.RGBA()
	r2, g2, b2, a2 := c2.RGBA()
	var diff int64
	diff += abs(int64(r1) - int64(r2))
	diff += abs(int64(g1) - int64(g2))
	diff += abs(int64(b1) - int64(b2))
	diff += abs(int64(a1) - int64(a2))
	return diff
}

func abs(x int64) int64 {
	if x < 0 {
		return -x
	}
	return x
}