// 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 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