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.
5 // This example demonstrates decoding a JPEG image and examining its pixels.
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:
24 func Example_decodeConfig() {
25 reader := base64.NewDecoder(base64.StdEncoding, strings.NewReader(data))
26 config, format, err := image.DecodeConfig(reader)
30 fmt.Println("Width:", config.Width, "Height:", config.Height, "Format:", format)
34 // Decode the JPEG data. If reading from file, create a reader with
36 // reader, err := os.Open("testdata/video-001.q50.420.jpeg")
40 // defer reader.Close()
41 reader := base64.NewDecoder(base64.StdEncoding, strings.NewReader(data))
42 m, _, err := image.Decode(reader)
48 // Calculate a 16-bin histogram for m's red, green, blue and alpha components.
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].
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])
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
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