iPhone BitmapImageRep

Question

I have a buffer which has JPEG image data. I need to display this image in UIImageView. I need to convert this image buffer into an object of UIImage and use it as follows

NSData *data = [NSData dataWithContentsOfFile:appFile]; UIImage *theImage = [[UIImage alloc] initWithData:data];

I get the image displayed but with a low resolution as compared to the actual resolution. Do I need to convert it into a Bitmap first and then use it with UIImage? I don't seem to be able to use NSBitmapImageRep. Any ideas on how can this be achieved?

Answer 1

If the UIImageView frame dimensions are different than the source image dimensions, you'll get a resized version of the image. The quality can be pretty rough depending on how much of a conversion is being performed.

I found this code on the net somewhere (sorry original author - I've lost the attribution) that performs a smoother resize:

UIImage* resizedImage(UIImage *inImage, CGRect thumbRect)
{
    CGImageRef   imageRef = [inImage CGImage];
    CGImageAlphaInfo alphaInfo = CGImageGetAlphaInfo(imageRef);

    // There's a wierdness with kCGImageAlphaNone and CGBitmapContextCreate
    // see Supported Pixel Formats in the Quartz 2D Programming Guide
    // Creating a Bitmap Graphics Context section
    // only RGB 8 bit images with alpha of kCGImageAlphaNoneSkipFirst, kCGImageAlphaNoneSkipLast, kCGImageAlphaPremultipliedFirst,
    // and kCGImageAlphaPremultipliedLast, with a few other oddball image kinds are supported
    // The images on input here are likely to be png or jpeg files
    if (alphaInfo == kCGImageAlphaNone)
     alphaInfo = kCGImageAlphaNoneSkipLast;

    // Build a bitmap context that's the size of the thumbRect
    CGContextRef bitmap = CGBitmapContextCreate(
               NULL,
               thumbRect.size.width,  // width
               thumbRect.size.height,  // height
               CGImageGetBitsPerComponent(imageRef), // really needs to always be 8
               4 * thumbRect.size.width, // rowbytes
               CGImageGetColorSpace(imageRef),
               alphaInfo
               );

    // Draw into the context, this scales the image
    CGContextDrawImage(bitmap, thumbRect, imageRef);

    // Get an image from the context and a UIImage
    CGImageRef ref = CGBitmapContextCreateImage(bitmap);
    UIImage* result = [UIImage imageWithCGImage:ref];

    CGContextRelease(bitmap); // ok if NULL
    CGImageRelease(ref);

    return result;
}