Question

I need to create an UIImage from a byte array.
Here is now I create the byte array:

image = CGImageCreateWithImageInRect(aux.CGImage, imageRect);
context = CGBitmapContextCreate (data[i][j], TILE_WIDTH, TILE_HEIGHT, 
                                 bitsPerComponent, bitmapBytesPerRow, colorSpace,
                                 kCGImageAlphaPremultipliedLast | kCGBitmapByteOrder32Big);//kCGImageAlphaNoneSkipFirst);//kCGImageAlphaNone);//

CGContextDrawImage(context, CGRectMake(0, 0, TILE_WIDTH, TILE_HEIGHT), image);

data[i][j] = CGBitmapContextGetData (context);

The data variable is an unsigned char.

And this is how I try to get the UIImage:

NSData *imgData = [NSData dataWithBytes:data[i][j] length:TILE_WIDTH*TILE_HEIGHT*numberOfCompponents];
        UIImage *img = [UIImage imageWithData: imgData];

The img (UIImage) is remaining nil.

OK, not this is the background: I am trying to create a pixelate application :). The images from the iPhone 4 camera are too big in size, so I split the image in smaller images. Doing so, when the area pixelated (touched) needs to be updated in order for the pixelate effect to be displayed, I am updating a smaller UIImage. I needed to do it like this because in previous tests it seamed like the update of an UIImage is killing the CPU. Still, the smaller images are now around 80×100 pxl, and the update is not working as smooth as possible. Sometimes, if you move the finger to fast it misses some spots :D. I think that using this method to create an UIImage from the byte array is faster than this one:

CGImageRef cgImage = CGImageCreate(TILE_WIDTH, TILE_HEIGHT, bitsPerComponent,
                                   bitsPerPixel, bitmapBytesPerRow, colorSpace, kCGImageAlphaPremultipliedLast | kCGBitmapByteOrder32Big, 
                                   dataProvider, NULL, false, kCGRenderingIntentDefault);
UIImage *imageToBeUpdated = [UIImage imageWithCGImage:cgImage];

Am I correct?

Answer 1

[UIImage imageWithData:data] parses data that is in a known image file format (e.g. jpeg, png, or gif; full list in the documentation. You’re passing it raw pixel data, which is not supported.

Try this instead of CGBitmapContextGetData to get the image out of the context:

CGImageRef imgRef = CGBitmapContextCreateImage(context);
UIImage *img = [UIImage imageWithCGImage:imgRef];