Convert UIImage to 8 bits - ios

Question

I wish to convert a UIImage to 8 bits. I have attempted to do this but I am not sure if I have done it right because I am getting a message later when I try to use the image proccessing library leptonica that states it is not 8 bits. Can anyone tell me if I am doing this correctly or the code on how to do it?
Thanks!
CODE
CGImageRef myCGImage = image.CGImage;
CFDataRef data = CGDataProviderCopyData(CGImageGetDataProvider(myCGImage));
const UInt8 *imageData = CFDataGetBytePtr(data);

Answer 1

Following code will work for images without alpha channel:
CGImageRef c = [[UIImage imageNamed:#"100_3077"] CGImage];
size_t bitsPerPixel = CGImageGetBitsPerPixel(c);
size_t bitsPerComponent = CGImageGetBitsPerComponent(c);
size_t width = CGImageGetWidth(c);
size_t height = CGImageGetHeight(c);
CGImageAlphaInfo a = CGImageGetAlphaInfo(c);
NSAssert(bitsPerPixel == 32 && bitsPerComponent == 8 && a == kCGImageAlphaNoneSkipLast, #"unsupported image type supplied");
CGContextRef targetImage = CGBitmapContextCreate(NULL, width, height, 8, 1 * CGImageGetWidth(c), CGColorSpaceCreateDeviceGray(), kCGImageAlphaNone);
UInt32 *sourceData = (UInt32*)[((__bridge_transfer NSData*) CGDataProviderCopyData(CGImageGetDataProvider(c))) bytes];
UInt32 *sourceDataPtr;
UInt8 *targetData = CGBitmapContextGetData(targetImage);
UInt8 r,g,b;
uint offset;
for (uint y = 0; y < height; y++)
{
for (uint x = 0; x < width; x++)
{
offset = y * width + x;
if (offset+2 < width * height)
{
sourceDataPtr = &sourceData[y * width + x];
r = sourceDataPtr[0+0];
g = sourceDataPtr[0+1];
b = sourceDataPtr[0+2];
targetData[y * width + x] = (r+g+b) / 3;
}
}
}
CGImageRef newImageRef = CGBitmapContextCreateImage(targetImage);
UIImage *newImage = [UIImage imageWithCGImage:newImageRef];
CGContextRelease(targetImage);
CGImageRelease(newImageRef);
With this code I converted an rgb image to an grayscale image:
Hope this helps