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POCore Graphics & GIF Color Table
 

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  1. POCore Graphics & GIF Color Table
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    <p>I am trying to limit the number of colors of an animated GIF (created from an array of <code>CGImageRef</code>).</p> <p>However, I am have difficulty actually setting the custom color table. Does anyone know how to do this with Core Graphics?</p> <p>I know of <code>kCGImagePropertyGIFImageColorMap</code>. Below is some test code (borrowing heavily from <a href="https://gist.github.com/792829" rel="nofollow">this github gist</a> -- since it's the only instance of <code>kCGImagePropertyGIFImageColorMap</code> Google could find).</p> <pre><code>NSString *path = [@"~/Desktop/test.png" stringByExpandingTildeInPath]; CGDataProviderRef imgDataProvider = CGDataProviderCreateWithCFData((CFDataRef)[NSData dataWithContentsOfFile:path]); CGImageRef image = CGImageCreateWithPNGDataProvider(imgDataProvider, NULL, true, kCGRenderingIntentDefault); const uint8_t colorTable[ 8 ] = { 0, 0, 0, 0, 255, 255, 255 , 255}; NSData* colorTableData = [ NSData dataWithBytes: colorTable length: 8 ]; NSMutableDictionary *gifProps = [NSMutableDictionary dictionary]; [gifProps setObject:colorTableData forKey:(NSString *)kCGImagePropertyGIFImageColorMap]; [gifProps setObject:[NSNumber numberWithBool:NO] forKey:(NSString *)kCGImagePropertyGIFHasGlobalColorMap]; NSDictionary* imgProps = [ NSDictionary dictionaryWithObject: gifProps forKey: (NSString*) kCGImagePropertyGIFDictionary ]; NSURL* destUrl = [NSURL fileURLWithPath:[@"~/Desktop/test.gif" stringByExpandingTildeInPath]]; CGImageDestinationRef dst = CGImageDestinationCreateWithURL( (CFURLRef) destUrl, kUTTypeGIF, 1, NULL ); CGImageDestinationAddImage( dst, image, imgProps ); CGImageDestinationSetProperties(dst, (CFDictionaryRef) imgProps); CGImageDestinationFinalize( dst ); CFRelease( dst ); </code></pre> <p>This, however, does not produce a black &amp; white image.</p> <p>Furthermore, I've tried opening a GIF to find the color table information, but that's providing little help.</p> <pre><code>CGImageSourceRef imageSourceRef = CGImageSourceCreateWithURL((CFURLRef) destUrl, NULL); NSDictionary *dict = (NSDictionary *)CGImageSourceCopyPropertiesAtIndex(imageSourceRef,0, NULL); CGImageRef img = CGImageSourceCreateImageAtIndex(imageSourceRef, 0, NULL); printf("Color space model: %d, indexed=%d, rgb = %d\n", CGColorSpaceGetModel(CGImageGetColorSpace(img)), kCGColorSpaceModelIndexed,kCGColorSpaceModelRGB); NSLog(@"%@", dict); </code></pre> <p>It says the color space is RGB for GIFs. Yet, if I try that code with an indexed PNG, it says the color space is indexed.</p> <p>Furthermore, all the GIFs I've tried have a image dictionary that looks roughly like the following:</p> <pre><code>{ ColorModel = RGB; Depth = 8; HasAlpha = 1; PixelHeight = 176; PixelWidth = 314; "{GIF}" = { DelayTime = "0.1"; UnclampedDelayTime = "0.04"; }; } </code></pre> <p>(If I use <code>CGImageSourceCopyProperties(...)</code>, it mentions a global color map, but again no color table is provided.)</p>
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