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Diffstat (limited to 'src/image/decode_example_test.go')
| -rw-r--r-- | src/image/decode_example_test.go | 149 |
1 files changed, 149 insertions, 0 deletions
diff --git a/src/image/decode_example_test.go b/src/image/decode_example_test.go new file mode 100644 index 0000000..526c03f --- /dev/null +++ b/src/image/decode_example_test.go @@ -0,0 +1,149 @@ +// Copyright 2012 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. + +// This example demonstrates decoding a JPEG image and examining its pixels. +package image_test + +import ( + "encoding/base64" + "fmt" + "image" + "log" + "strings" + + // Package image/jpeg is not used explicitly in the code below, + // but is imported for its initialization side-effect, which allows + // image.Decode to understand JPEG formatted images. Uncomment these + // two lines to also understand GIF and PNG images: + // _ "image/gif" + // _ "image/png" + _ "image/jpeg" +) + +func Example_decodeConfig() { + reader := base64.NewDecoder(base64.StdEncoding, strings.NewReader(data)) + config, format, err := image.DecodeConfig(reader) + if err != nil { + log.Fatal(err) + } + fmt.Println("Width:", config.Width, "Height:", config.Height, "Format:", format) +} + +func Example() { + // Decode the JPEG data. If reading from file, create a reader with + // + // reader, err := os.Open("testdata/video-001.q50.420.jpeg") + // if err != nil { + // log.Fatal(err) + // } + // defer reader.Close() + reader := base64.NewDecoder(base64.StdEncoding, strings.NewReader(data)) + m, _, err := image.Decode(reader) + if err != nil { + log.Fatal(err) + } + bounds := m.Bounds() + + // Calculate a 16-bin histogram for m's red, green, blue and alpha components. + // + // An image's bounds do not necessarily start at (0, 0), so the two loops start + // at bounds.Min.Y and bounds.Min.X. Looping over Y first and X second is more + // likely to result in better memory access patterns than X first and Y second. + var histogram [16][4]int + for y := bounds.Min.Y; y < bounds.Max.Y; y++ { + for x := bounds.Min.X; x < bounds.Max.X; x++ { + r, g, b, a := m.At(x, y).RGBA() + // A color's RGBA method returns values in the range [0, 65535]. + // Shifting by 12 reduces this to the range [0, 15]. + histogram[r>>12][0]++ + histogram[g>>12][1]++ + histogram[b>>12][2]++ + histogram[a>>12][3]++ + } + } + + // Print the results. + fmt.Printf("%-14s %6s %6s %6s %6s\n", "bin", "red", "green", "blue", "alpha") + for i, x := range histogram { + 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]) + } + // Output: + // bin red green blue alpha + // 0x0000-0x0fff: 364 790 7242 0 + // 0x1000-0x1fff: 645 2967 1039 0 + // 0x2000-0x2fff: 1072 2299 979 0 + // 0x3000-0x3fff: 820 2266 980 0 + // 0x4000-0x4fff: 537 1305 541 0 + // 0x5000-0x5fff: 319 962 261 0 + // 0x6000-0x6fff: 322 375 177 0 + // 0x7000-0x7fff: 601 279 214 0 + // 0x8000-0x8fff: 3478 227 273 0 + // 0x9000-0x9fff: 2260 234 329 0 + // 0xa000-0xafff: 921 282 373 0 + // 0xb000-0xbfff: 321 335 397 0 + // 0xc000-0xcfff: 229 388 298 0 + // 0xd000-0xdfff: 260 414 277 0 + // 0xe000-0xefff: 516 428 298 0 + // 0xf000-0xffff: 2785 1899 1772 15450 +} + +const data = ` +/9j/4AAQSkZJRgABAQIAHAAcAAD/2wBDABALDA4MChAODQ4SERATGCgaGBYWGDEjJR0oOjM9PDkzODdA +SFxOQERXRTc4UG1RV19iZ2hnPk1xeXBkeFxlZ2P/2wBDARESEhgVGC8aGi9jQjhCY2NjY2NjY2NjY2Nj +Y2NjY2NjY2NjY2NjY2NjY2NjY2NjY2NjY2NjY2NjY2NjY2NjY2P/wAARCABnAJYDASIAAhEBAxEB/8QA +HwAAAQUBAQEBAQEAAAAAAAAAAAECAwQFBgcICQoL/8QAtRAAAgEDAwIEAwUFBAQAAAF9AQIDAAQRBRIh +MUEGE1FhByJxFDKBkaEII0KxwRVS0fAkM2JyggkKFhcYGRolJicoKSo0NTY3ODk6Q0RFRkdISUpTVFVW +V1hZWmNkZWZnaGlqc3R1dnd4eXqDhIWGh4iJipKTlJWWl5iZmqKjpKWmp6ipqrKztLW2t7i5usLDxMXG +x8jJytLT1NXW19jZ2uHi4+Tl5ufo6erx8vP09fb3+Pn6/8QAHwEAAwEBAQEBAQEBAQAAAAAAAAECAwQF +BgcICQoL/8QAtREAAgECBAQDBAcFBAQAAQJ3AAECAxEEBSExBhJBUQdhcRMiMoEIFEKRobHBCSMzUvAV +YnLRChYkNOEl8RcYGRomJygpKjU2Nzg5OkNERUZHSElKU1RVVldYWVpjZGVmZ2hpanN0dXZ3eHl6goOE +hYaHiImKkpOUlZaXmJmaoqOkpaanqKmqsrO0tba3uLm6wsPExcbHyMnK0tPU1dbX2Nna4uPk5ebn6Onq +8vP09fb3+Pn6/9oADAMBAAIRAxEAPwDlwKMD0pwzSiuK57QzGDxS7D6in8Y5ximnAPUfSlcq4m3ilUYp +2OKXHvRcVxnTtS7c07HNFK4DQPakC4PNOA+tOx70XAjK/So5gBGP94fzqfvUVx/qxx/EP51UXqRP4WSE +cmgjilP3jSEZqS0IO/NGDnpUiocDg/McDjvV6HTPOdVWYgsM5KcfzzQ2JySM2jp6VYu7SWzmMUwG4cgj +kMPUVBjjtTGtRu0Zopw+lFFxhinrGzuqqMsxAA9yaXFSRv5cqSEcIwYj6GpuZ30O30fSLKzhUpbpNMv3 +5XGTn29BV28jt7pPLuIVljPBBFVreYx+VbqAjycgt3x14zRcNOxGyVFHQkIc/wA61exyKLbuzjdZ046d +ftEuTEw3Rk9SPT8P8Kpbea3tchbyVae4JkjbbGpGdwOM89Af6ViFTWUtGdcXoM2+woK1JtpNtTcoZt+l +Jt7ZqTbRtouFyPFRXI/c9D94fzqzioLsfuD/ALw/nVReqIn8LJCOTSY+tSMOTmkIpXLRu+F0t5pJxPHG +wjjUAuBjJJz1+laD6Pai+WaK9SBX6puzn6ZP+NV/Dkdtc6ZNbyAFwxLAHDYPv6VoQ21nPNEEiQGEFRtk +Gf0NaWTOeW7Of8QwGG4MRZnEbYXPJwRnOR0zWNXW+KrqBLUWi5EjbWCgcAA9c/gRXKYqZaGlK/LqMH0F 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