Resize Image High Quality

[vocaro]

Originally Posted by PhoneyDeveloper

//	resizedImage
...

Phoney, there are some problems with your code. In particular, the last parameter takes a CGBitmapInfo type, but you're passing a CGImageAlphaInfo type. This can chop off the byte ordering information stored in CGBitmapInfo, resulting in odd problems such as pink-tinted images. Also, you're hard coding the bytesPerRow value when in fact it should be based on the original image. The following is a revised version of your code:

// Returns a rescaled copy of the image; its imageOrientation will be UIImageOrientationUp
// If the new size is not integral, it will be rounded up
- (UIImage *)makeResizedImage:(CGSize)newSize quality:(CGInterpolationQuality)interpolationQuality {
    CGRect newRect = CGRectIntegral(CGRectMake(0, 0, newSize.width, newSize.height));
    CGImageRef imageRef = self.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];
    
    // Clean up
    CGContextRelease(bitmap);
    CGImageRelease(resizedImageRef);
    
    return resizedImage;
}

As with your original function, this code works as expected only when UIImage.imageOrientation == UIImageOrientationUp.

[StevenD]

Hi,
Boy, this is such a newbie question, but I need to use Phoney's code for shrinking an image, and I can't figure out how to call the function:

UIImage *imgMyShrunkenImage = ?????

In my code, I turned phoney's
UIImage* resizedImage(UIImage *inImage, CGRect thumbRect)

into:
-(UIImage*)resizedImage:(UIImage*)inImage inRect:(CGRect)thumbRect {

because I'm more familiar with that syntax, but I need to know how to complete the line that calls the funtion or method, passing an image and a rect, and creating a UIImage that I can then use.

Thanks for any help.
/Steve

[vocaro]

I'm not sure how one can be familiar with the syntax of a declaration and yet be unfamiliar with its invocation, but anyway... Have you considered:

UIImage *imgMyShrunkenImage = [self resizedImage:img inRect:rect];

[StevenD]

Thanks, vocaro,

Sorry. Total brain f**t. I guess I was so excited to find this post, phoney's code, and also especially the code you referred us to, which takes image orientation into account. *Incredibly* useful for the app I'm working on. Lifesaver. Thanks.

/Steve

[yoichi]

Originally Posted by shawn

Thanks Phoney! With a few tweaks that method worked great with no warnings!

Hi Shawn, what was your tweak to the PhonyDeveloper's code?

Is that something similar to vocaro's code on page 2 of this thread?

Thanks,
Yoichi

[maintainer]

I made two method for reszing.

#2 incorrectly resize some images in _sumlator_

[inzamam]

if you want to resize image than i will you suggest you to visit the below link
Learn & Share your experience! • View topic - Resizing image using asp.net-2.0(vb)
please visit the link, here you can know about how to resize image.
thank you very much.

[baja_yu]

How on Earth is ASP/VB .Net related to anything here?

[DimplePanchal]

// 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

How to get rid of this ??