// Courtesy of Apple, Create Bitmap with Alpha/RGB values
CGContextRef CreateARGBBitmapContext (CGImageRef inImage, CGSize size)
{
CGContextRef context = NULL;
CGColorSpaceRef colorSpace;
void * bitmapData;
int bitmapByteCount;
int bitmapBytesPerRow;
size_t pixelsWide = size.width;
size_t pixelsHigh = size.height;
bitmapBytesPerRow = (pixelsWide * 4); //ARGB
bitmapByteCount = (bitmapBytesPerRow * pixelsHigh);
colorSpace = CGColorSpaceCreateDeviceRGB();
if (colorSpace == NULL)
{
fprintf(stderr, "Error allocating color space\n");
return NULL;
}
// allocate the bitmap & create context
bitmapData = malloc( bitmapByteCount );
if (bitmapData == NULL)
{
fprintf (stderr, "Memory not allocated!");
CGColorSpaceRelease( colorSpace );
return NULL;
}
context = CGBitmapContextCreate (bitmapData, pixelsWide, pixelsHigh, 8,
bitmapBytesPerRow, colorSpace,
kCGImageAlphaPremultipliedFirst);
if (context == NULL)
{
free (bitmapData);
fprintf (stderr, "Context not created!");
}
CGColorSpaceRelease( colorSpace );
return context;
}
// Return a C-based bitmap of the image data inside an image
unsigned char *RequestImagePixelData(UIImage *inImage)
{
CGImageRef img = [inImage CGImage];
CGSize size = [inImage size];
CGContextRef cgctx = CreateARGBBitmapContext(img, size);
if (cgctx == NULL) return NULL;
CGRect rect = {{0,0},{size.width, size.height}};
CGContextDrawImage(cgctx, rect, img);
unsigned char *data = CGBitmapContextGetData (cgctx);
CGContextRelease(cgctx);
return data;
}
使用位图某像素:
[UIColor
colorWithRed: (float) (bitmap[startByte+1]/255.0f)
green: (float) (bitmap[startByte+2]/255.0f)
blue: (float) (bitmap[startByte+3]/255.0f)
alpha: (float)(bitmap[startByte]]