Question

Actually i have used following two methods for image resize but my client says me that image quality is very poor so i want to know what should be the best method for image resizing.
I am just taking the screenshots and send this screenshot of 480×320 size UIImage to the following function.

- (UIImage *)makeResizedImage:(CGSize)newSize quality:(CGInterpolationQuality)interpolationQuality image:(UIImage *)inImage{
    NSLog(@"OriginalImage%f",inImage.size.width);

    CGRect newRect = CGRectIntegral(CGRectMake(0, 0, newSize.width, newSize.height));

    CGImageRef imageRef = [inImage CGImage];
    // Compute the bytes per row of the new image
    size_t bytesPerRow = CGImageGetBitsPerPixel(imageRef) / CGImageGetBitsPerComponent(imageRef) * newRect.size.width;
    bytesPerRow = (bytesPerRow + 15) & ~15;  // Make it 16-byte aligned

    // Build a bitmap context that's the same dimensions as the new size
    CGContextRef bitmap = CGBitmapContextCreate(NULL,
                                                newRect.size.width,
                                                newRect.size.height,
                                                CGImageGetBitsPerComponent(imageRef),
                                                bytesPerRow,
                                                CGImageGetColorSpace(imageRef),
                                                CGImageGetBitmapInfo(imageRef));

    CGContextSetInterpolationQuality(bitmap, interpolationQuality);

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

    // Get the resized image from the context and a UIImage
    CGImageRef resizedImageRef = CGBitmapContextCreateImage(bitmap);
    UIImage *resizedImage = [UIImage imageWithCGImage:resizedImageRef];
    NSLog(@"ResizedImage%f",resizedImage.size.width);
    NSLog(@"ResizedImage%f",resizedImage.size.height);

    // Clean up
    CGContextRelease(bitmap);
    CGImageRelease(resizedImageRef);

    return resizedImage;
}

or

- (UIImage *)resizedImage:(CGSize)newSize
                transform:(CGAffineTransform)transform
           drawTransposed:(BOOL)transpose
     interpolationQuality:(CGInterpolationQuality)quality {
    CGRect newRect = CGRectIntegral(CGRectMake(0, 0, newSize.width, newSize.height));
    CGRect transposedRect = CGRectMake(0, 0, newRect.size.height, newRect.size.width);
    CGImageRef imageRef = self.CGImage;

    // Build a context that's the same dimensions as the new size
    CGContextRef bitmap = CGBitmapContextCreate(NULL,
                                                newRect.size.width,
                                                newRect.size.height,
                                                CGImageGetBitsPerComponent(imageRef),
                                                0,
                                                CGImageGetColorSpace(imageRef),
                                                CGImageGetBitmapInfo(imageRef));

    // Rotate and/or flip the image if required by its orientation
    CGContextConcatCTM(bitmap, transform);

    // Set the quality level to use when rescaling
    CGContextSetInterpolationQuality(bitmap, quality);

    // Draw into the context; this scales the image
    CGContextDrawImage(bitmap, transpose ? transposedRect : newRect, imageRef);

    // Get the resized image from the context and a UIImage
    CGImageRef newImageRef = CGBitmapContextCreateImage(bitmap);
    UIImage *newImage = [UIImage imageWithCGImage:newImageRef];

    // Clean up
    CGContextRelease(bitmap);
    CGImageRelease(newImageRef);

    return newImage;
}

please tell me is there any other method to resize the image without losing its quality

Answer 1

You might try integrating a library instead of rolling your own.

Here is one: http://code.google.com/p/simple-iphone-image-processing/