Getting the pixel data from a CGImage object(Objective-c取得图像的像素信息)
Q: How do I access the pixel data of a CGImage object?
A: On Mac OS X 10.5 or later, a new call has been added that allows you to obtain the actual pixel data from a CGImage object. This call, CGDataProviderCopyData, returns a CFData object that contains the pixel data from the image in question. An example of using this call to obtain pixel data from a CGImage is shown in Listing 1. Once you have the CFData object with your pixel information, you can call CFDataGetBytePtr to get a pointer to the pixel data, or CFDataGetBytes to copy a subrange of pixel data.
CFDataRef CopyImagePixels(CGImageRef inImage){ return CGDataProviderCopyData(CGImageGetDataProvider(inImage));}
Listing 2: Accessing the pixel data of a CGImage.void ManipulateImagePixelData(CGImageRef inImage){ // Create the bitmap context CGContextRef cgctx = CreateARGBBitmapContext(inImage); if (cgctx == NULL) { // error creating context return; } // Get image width, height. We'll use the entire image. size_t w = CGImageGetWidth(inImage); size_t h = CGImageGetHeight(inImage); CGRect rect = {{0,0},{w,h}}; // Draw the image to the bitmap context. Once we draw, the memory // allocated for the context for rendering will then contain the // raw image data in the specified color space. CGContextDrawImage(cgctx, rect, inImage); // Now we can get a pointer to the image data associated with the bitmap // context. void *data = CGBitmapContextGetData (cgctx); if (data != NULL) { // **** You have a pointer to the image data **** // **** Do stuff with the data here **** } // When finished, release the context CGContextRelease(cgctx); // Free image data memory for the context if (data) { free(data); }}CGContextRef CreateARGBBitmapContext (CGImageRef inImage){ CGContextRef context = NULL; CGColorSpaceRef colorSpace; void * bitmapData; int bitmapByteCount; int bitmapBytesPerRow; // Get image width, height. We'll use the entire image. size_t pixelsWide = CGImageGetWidth(inImage); size_t pixelsHigh = CGImageGetHeight(inImage); // Declare the number of bytes per row. Each pixel in the bitmap in this // example is represented by 4 bytes; 8 bits each of red, green, blue, and // alpha. bitmapBytesPerRow = (pixelsWide * 4); bitmapByteCount = (bitmapBytesPerRow * pixelsHigh); // Use the generic RGB color space. colorSpace = CGColorSpaceCreateWithName(kCGColorSpaceGenericRGB); if (colorSpace == NULL) { fprintf(stderr, "Error allocating color space\n"); return NULL; } // Allocate memory for image data. This is the destination in memory // where any drawing to the bitmap context will be rendered. bitmapData = malloc( bitmapByteCount ); if (bitmapData == NULL) { fprintf (stderr, "Memory not allocated!"); CGColorSpaceRelease( colorSpace ); return NULL; } // Create the bitmap context. We want pre-multiplied ARGB, 8-bits // per component. Regardless of what the source image format is // (CMYK, Grayscale, and so on) it will be converted over to the format // specified here by CGBitmapContextCreate. context = CGBitmapContextCreate (bitmapData, pixelsWide, pixelsHigh, 8, // bits per component bitmapBytesPerRow, colorSpace, kCGImageAlphaPremultipliedFirst); if (context == NULL) { free (bitmapData); fprintf (stderr, "Context not created!"); } // Make sure and release colorspace before returning CGColorSpaceRelease( colorSpace ); return context;}
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原文地址：http://developer.apple.com/library/mac/#qa/qa2007/qa1509.html
