[iPhone] UIImage pixel manipulation

Question

Hello all,
I want to get the pixel data of an UIImage, fiddle with the pixels and create a new UIImage from that modified pixel data. However, I fail. The information provided [here|http://developer.apple.com/qa/qa2007/qa1509.html] doesn't seem to work on iPhones. Somehow the image always has 3 components (even when I created it with an alpha channel) but when I try to create a 24 bit context I get an "unsupported parameter combination" error like:
unsupported parameter combination: 8 integer bits/component; 24 bits/pixel; 3-component colorspace; kCGImageAlphaNone; 66 bytes/row.
because it's invalid, according to [this info|http://developer.apple.com/qa/qa2001/qa1037.html]. But when I create an 4 component context the image is all garbeld up and looks like colorful noise. I created a simple test case where I just get the image data and create a new image from that very data. This should return an image that looks exactly like the original, but it fails due to the problems mentioned above. Does anybody have an idea?
Thanks and regards,
Sebastian Mecklenburg
UIImage* manipulateImage (UIImage* inImage)
CGImageRef image = inImage.CGImage;
CGContextRef context = NULL;
CGColorSpaceRef colorSpace;
void * bitmapData;
int bitmapByteCount;
int bitmapBytesPerRow;
int bitsPerComponent = 8;
// Use the generic RGB color space.
colorSpace = CGColorSpaceCreateDeviceRGB();//CGImageGetColorSpace(image);//
if (colorSpace == NULL) {
fprintf(stderr, "Error allocating color space
return NULL;
int numberOfCompponents = 4;//CGColorSpaceGetNumberOfComponents(colorSpace); //always returns 3 -> unsupported parameter combination
int bitsPerPixel = bitsPerComponent * numberOfCompponents;
size_t pixelsWide = CGImageGetWidth(image);
size_t pixelsHigh = CGImageGetHeight(image);
CGRect imageRect = {{0,0},{pixelsWide, pixelsHigh}};
// 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 * numberOfCompponents);
bitmapByteCount = (bitmapBytesPerRow * pixelsHigh);
// 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;
context = CGBitmapContextCreate (bitmapData, pixelsWide, pixelsHigh,
bitsPerComponent, bitmapBytesPerRow, colorSpace,
kCGImageAlphaPremultipliedFirst);//kCGImageAlphaNoneSkipFirst);//kCGImageAlphaNone);//
if (context == NULL) {
free (bitmapData);
fprintf (stderr, "Context not created!");
CGColorSpaceRelease( colorSpace );
return NULL;
CGContextDrawImage(context, imageRect, image);
void *data = CGBitmapContextGetData (context);
//do something with data
CGDataProviderRef dataProvider = CGDataProviderCreateWithData(NULL, data, bitmapByteCount, NULL);
CGImageRef cgImage = CGImageCreate(pixelsWide, pixelsHigh, bitsPerComponent,
bitsPerPixel, bitmapBytesPerRow, colorSpace, kCGImageAlphaPremultipliedFirst,
dataProvider, NULL, false, kCGRenderingIntentDefault);
CGDataProviderRelease(dataProvider);
CGColorSpaceRelease(colorSpace);
// When finished, release the context
CGContextRelease(context);
// Free image data memory for the context
if (data) {
free(data);
return [UIImage imageWithCGImage:cgImage];

Answer 1

Hello all,
I want to get the pixel data of an UIImage, fiddle with the pixels and create a new UIImage from that modified pixel data. However, I fail. The information provided [here|http://developer.apple.com/qa/qa2007/qa1509.html] doesn't seem to work on iPhones. Somehow the image always has 3 components (even when I created it with an alpha channel) but when I try to create a 24 bit context I get an "unsupported parameter combination" error like:
unsupported parameter combination: 8 integer bits/component; 24 bits/pixel; 3-component colorspace; kCGImageAlphaNone; 66 bytes/row.
because it's invalid, according to [this info|http://developer.apple.com/qa/qa2001/qa1037.html]. But when I create an 4 component context the image is all garbeld up and looks like colorful noise. I created a simple test case where I just get the image data and create a new image from that very data. This should return an image that looks exactly like the original, but it fails due to the problems mentioned above. Does anybody have an idea?
Thanks and regards,
Sebastian Mecklenburg
UIImage* manipulateImage (UIImage* inImage)
CGImageRef image = inImage.CGImage;
CGContextRef context = NULL;
CGColorSpaceRef colorSpace;
void * bitmapData;
int bitmapByteCount;
int bitmapBytesPerRow;
int bitsPerComponent = 8;
// Use the generic RGB color space.
colorSpace = CGColorSpaceCreateDeviceRGB();//CGImageGetColorSpace(image);//
if (colorSpace == NULL) {
fprintf(stderr, "Error allocating color space
return NULL;
int numberOfCompponents = 4;//CGColorSpaceGetNumberOfComponents(colorSpace); //always returns 3 -> unsupported parameter combination
int bitsPerPixel = bitsPerComponent * numberOfCompponents;
size_t pixelsWide = CGImageGetWidth(image);
size_t pixelsHigh = CGImageGetHeight(image);
CGRect imageRect = {{0,0},{pixelsWide, pixelsHigh}};
// 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 * numberOfCompponents);
bitmapByteCount = (bitmapBytesPerRow * pixelsHigh);
// 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;
context = CGBitmapContextCreate (bitmapData, pixelsWide, pixelsHigh,
bitsPerComponent, bitmapBytesPerRow, colorSpace,
kCGImageAlphaPremultipliedFirst);//kCGImageAlphaNoneSkipFirst);//kCGImageAlphaNone);//
if (context == NULL) {
free (bitmapData);
fprintf (stderr, "Context not created!");
CGColorSpaceRelease( colorSpace );
return NULL;
CGContextDrawImage(context, imageRect, image);
void *data = CGBitmapContextGetData (context);
//do something with data
CGDataProviderRef dataProvider = CGDataProviderCreateWithData(NULL, data, bitmapByteCount, NULL);
CGImageRef cgImage = CGImageCreate(pixelsWide, pixelsHigh, bitsPerComponent,
bitsPerPixel, bitmapBytesPerRow, colorSpace, kCGImageAlphaPremultipliedFirst,
dataProvider, NULL, false, kCGRenderingIntentDefault);
CGDataProviderRelease(dataProvider);
CGColorSpaceRelease(colorSpace);
// When finished, release the context
CGContextRelease(context);
// Free image data memory for the context
if (data) {
free(data);
return [UIImage imageWithCGImage:cgImage];