iPhone Difference Handling Images Between Device and Simulator - iphone

Question

I have an image with a transparent border, and I am trying to directly manipulate the image pixels, following the Apple guide found here. Everything works perfectly well when run on the device. However, when I run my code on the simulator, I find that the transparent border of the image slowly turns black with each call to this function. The strange thing is that even if I don't modify the image data, the transparent border still begins to turn black with each call to this function. For example, I see the same problem even if my image manipulation code calls CGBitmapContextGetData but doesn't use the returned data pointer. To make the problem go away on the simulator, I have to comment out the call to CGBitmapContextGetData (and the freeing of the data pointer of course). Example code that still modifies the image on the simulator:
+ (UIImage *) updateImage:(UIImage *)inputImage
{
UIImage *updatedImage;
/* Update colors in image appropriately */
CGImageRef image = [inputImage CGImage];
CGContextRef cgctx = [ColorHandler CreateARGBBitmapContext:image];
if (cgctx == NULL)
{
// error creating context
NSLog(#"Error creating context.\n");
return nil;
}
size_t w = CGImageGetWidth(image);
size_t h = CGImageGetHeight(image);
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, image);
// Now we can get a pointer to the image data associated with the bitmap
// context.
void *data = CGBitmapContextGetData(cgctx);
CGImageRef ref = CGBitmapContextCreateImage(cgctx);
updatedImage = [UIImage imageWithCGImage:ref];
// When finished, release the context
CGContextRelease(cgctx);
CGImageRelease(ref);
// Free image data memory for the context
if (data)
{
free(data);
}
return updatedImage;
}
I read the comments and answers here regarding how images are managed differently between the device and simulator, but it hasn't helped me figure out my problem.
The only difference between my CreateARGBBitmapContext and the example one is that I call CGColorSpaceCreateDeviceRGB instead of CGColorSpaceCreateWithName because I am targeting iOS. The image is edited exactly as designed when run on the iOS device.
I am currently doing all image manipulation in the main thread for debugging this issue.
Specs: Mountain Lion, XCode 4.5.2, iOS 6 device, iOS 6 simulator

Answer 1

I was able to solve the issue by allowing Quartz to allocate and manage the memory for the bitmap (Apple doc). To do this, I updated the call to CGBitmapContextCreate in CreateARGBBitmapContext to pass NULL, and I removed all references to bitmapData.
// 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 (NULL,
pixelsWide,
pixelsHigh,
8, // bits per component
bitmapBytesPerRow,
colorSpace,
kCGImageAlphaPremultipliedFirst);
Then, in the updateImage method, I removed the freeing of data. Now it seems to work on both device and simulator without any issues.