1// Copyright 2012 The Go Authors. All rights reserved.
2// Use of this source code is governed by a BSD-style
3// license that can be found in the LICENSE file.
4
5// This example demonstrates decoding a JPEG image and examining its pixels.
6package image_test
7
8import (
9	"encoding/base64"
10	"fmt"
11	"image"
12	"log"
13	"strings"
14
15	// Package image/jpeg is not used explicitly in the code below,
16	// but is imported for its initialization side-effect, which allows
17	// image.Decode to understand JPEG formatted images. Uncomment these
18	// two lines to also understand GIF and PNG images:
19	// _ "image/gif"
20	// _ "image/png"
21	_ "image/jpeg"
22)
23
24func Example_decodeConfig() {
25	reader := base64.NewDecoder(base64.StdEncoding, strings.NewReader(data))
26	config, format, err := image.DecodeConfig(reader)
27	if err != nil {
28		log.Fatal(err)
29	}
30	fmt.Println("Width:", config.Width, "Height:", config.Height, "Format:", format)
31}
32
33func Example() {
34	// Decode the JPEG data. If reading from file, create a reader with
35	//
36	// reader, err := os.Open("testdata/video-001.q50.420.jpeg")
37	// if err != nil {
38	//     log.Fatal(err)
39	// }
40	// defer reader.Close()
41	reader := base64.NewDecoder(base64.StdEncoding, strings.NewReader(data))
42	m, _, err := image.Decode(reader)
43	if err != nil {
44		log.Fatal(err)
45	}
46	bounds := m.Bounds()
47
48	// Calculate a 16-bin histogram for m's red, green, blue and alpha components.
49	//
50	// An image's bounds do not necessarily start at (0, 0), so the two loops start
51	// at bounds.Min.Y and bounds.Min.X. Looping over Y first and X second is more
52	// likely to result in better memory access patterns than X first and Y second.
53	var histogram [16][4]int
54	for y := bounds.Min.Y; y < bounds.Max.Y; y++ {
55		for x := bounds.Min.X; x < bounds.Max.X; x++ {
56			r, g, b, a := m.At(x, y).RGBA()
57			// A color's RGBA method returns values in the range [0, 65535].
58			// Shifting by 12 reduces this to the range [0, 15].
59			histogram[r>>12][0]++
60			histogram[g>>12][1]++
61			histogram[b>>12][2]++
62			histogram[a>>12][3]++
63		}
64	}
65
66	// Print the results.
67	fmt.Printf("%-14s %6s %6s %6s %6s\n", "bin", "red", "green", "blue", "alpha")
68	for i, x := range histogram {
69		fmt.Printf("0x%04x-0x%04x: %6d %6d %6d %6d\n", i<<12, (i+1)<<12-1, x[0], x[1], x[2], x[3])
70	}
71	// Output:
72	// bin               red  green   blue  alpha
73	// 0x0000-0x0fff:    364    790   7242      0
74	// 0x1000-0x1fff:    645   2967   1039      0
75	// 0x2000-0x2fff:   1072   2299    979      0
76	// 0x3000-0x3fff:    820   2266    980      0
77	// 0x4000-0x4fff:    537   1305    541      0
78	// 0x5000-0x5fff:    319    962    261      0
79	// 0x6000-0x6fff:    322    375    177      0
80	// 0x7000-0x7fff:    601    279    214      0
81	// 0x8000-0x8fff:   3478    227    273      0
82	// 0x9000-0x9fff:   2260    234    329      0
83	// 0xa000-0xafff:    921    282    373      0
84	// 0xb000-0xbfff:    321    335    397      0
85	// 0xc000-0xcfff:    229    388    298      0
86	// 0xd000-0xdfff:    260    414    277      0
87	// 0xe000-0xefff:    516    428    298      0
88	// 0xf000-0xffff:   2785   1899   1772  15450
89}
90
91const data = `
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150