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Diffstat (limited to 'libgo/go/image/decode_example_test.go')
| -rw-r--r-- | libgo/go/image/decode_example_test.go | 79 |
1 files changed, 79 insertions, 0 deletions
diff --git a/libgo/go/image/decode_example_test.go b/libgo/go/image/decode_example_test.go new file mode 100644 index 00000000000..aa5a841c0a5 --- /dev/null +++ b/libgo/go/image/decode_example_test.go @@ -0,0 +1,79 @@ +// 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 ( + "fmt" + "image" + "log" + "os" + + // 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() { + // Open the file. + file, err := os.Open("testdata/video-001.jpeg") + if err != nil { + log.Fatal(err) + } + defer file.Close() + + // Decode the image. + m, _, err := image.Decode(file) + 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: 471 819 7596 0 + // 0x1000-0x1fff: 576 2892 726 0 + // 0x2000-0x2fff: 1038 2330 943 0 + // 0x3000-0x3fff: 883 2321 1014 0 + // 0x4000-0x4fff: 501 1295 525 0 + // 0x5000-0x5fff: 302 962 242 0 + // 0x6000-0x6fff: 219 358 150 0 + // 0x7000-0x7fff: 352 281 192 0 + // 0x8000-0x8fff: 3688 216 246 0 + // 0x9000-0x9fff: 2277 237 283 0 + // 0xa000-0xafff: 971 254 357 0 + // 0xb000-0xbfff: 317 306 429 0 + // 0xc000-0xcfff: 203 402 401 0 + // 0xd000-0xdfff: 256 394 241 0 + // 0xe000-0xefff: 378 343 173 0 + // 0xf000-0xffff: 3018 2040 1932 15450 +} |