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    <p>The program below takes an input file name and an output file name. It opens the input file, decodes it, converts it to grayscale, then encodes it to the output file.</p> <p>Thie program isn't specific to PNGs, but to support other file formats you'd have to import the correct image package. For example, to add JPEG support you could add to the imports list <code>_ "image/jpeg"</code>.</p> <p>If you <em>only</em> want to support PNG, then you can use <a href="http://golang.org/pkg/image/png/#Decode" rel="noreferrer">image/png.Decode</a> directly instead of <a href="http://golang.org/pkg/image/#Decode" rel="noreferrer">image.Decode</a>.</p> <pre><code>package main import ( "image" "image/png" // register the PNG format with the image package "os" ) func main() { infile, err := os.Open(os.Args[1]) if err != nil { // replace this with real error handling panic(err.String()) } defer infile.Close() // Decode will figure out what type of image is in the file on its own. // We just have to be sure all the image packages we want are imported. src, _, err := image.Decode(infile) if err != nil { // replace this with real error handling panic(err.String()) } // Create a new grayscale image bounds := src.Bounds() w, h := bounds.Max.X, bounds.Max.Y gray := image.NewGray(w, h) for x := 0; x &lt; w; x++ { for y := 0; y &lt; h; y++ { oldColor := src.At(x, y) grayColor := image.GrayColorModel.Convert(oldColor) gray.Set(x, y, grayColor) } } // Encode the grayscale image to the output file outfile, err := os.Create(os.Args[2]) if err != nil { // replace this with real error handling panic(err.String()) } defer outfile.Close() png.Encode(outfile, gray) } </code></pre>
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    1. POhow to read a png file in color and output as gray scale using the Go programming language?
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    1. USEvan Shaw
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    1. COI appreciate your quick response, however this opens an image as RGBA, as far as I know. What I need is a grayscale image, where each pixel is an 8-bit value.
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    2. COIf the PNG is encoded as a grayscale image, I believe the png package will decode it to an image.Gray. If that's not the case, I think there's either an error in the image or a bug in the package.
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    3. COThe image is not encoded as gray scale: I want to remove color. I want to convert from RGBA in the png file, to grayscale in the Image object in Go. I actually want to lose information, sorry if I wasn't clear.
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