| // 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() { |
| // 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 = ` |
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| ` |
