CoreGraphics Image resize

Question

This code is from Apple's WWDC 2011 Session 318 - iOS Performance in Depth and uses CoreGraphics to create thumbnails from server hosted images.

CGImageSourceRef src = CGImageSourceCreateWithURL(url);
NSDictionary *options = (CFDictionaryRef)[NSDictionary 
dictionaryWithObject:[NSNumber numberWithInt:1024
forKey:(id)kCGImageSourceThumbnailMaxPixelSize];

CGImageRef thumbnail = CGImageSourceCreateThumbnailAtIndex(src,0,options);
UIImage *image = [UIImage imageWithCGImage:thumbnail];
CGImageRelease(thumbnail);
CGImageSourceRelease(src);

But it doesnt work and the docs don't really help. In the iOS docs CGImageSource CGImageSourceRef CGImageSourceCreateThumbnailAtIndex are available

in Mac OS X v10.4 or later

How can I get this to work?

EDIT

These are the compiler errors I'm getting:

Use of undeclared identifier 'CGImageSourceRef'
Use of undeclared identifier 'kCGImageSourceThumbnailMaxPixelSize'
Use of undeclared identifier 'src'
Implicit declaration of function 'CGImageSourceCreateThumbnailAtIndex' is invalid in C99
Implicit declaration of function 'CGImageSourceRelease' is invalid in C99
Implicit declaration of function 'CGImageSourceCreateWithURL' is invalid in C99

iOS docs are actually [here](http://developer.apple.com/library/ios/#documentation/GraphicsImaging/Reference/CGImageSource/Reference/reference.html) and availabilaty is declared `in iOS 4.0 and later`. Try to state the exact source of problem. Do you even get a valid `src`. P.S. it's not a good idea to discuss WWDC sessions outside apple.developer forum - since all of referenced functions are not under NDA i guess you're o.k. :) — Rok Jarc, Jun 12 '12 at 09:41
Ah yep didnt see that iOS 4+ further down. Edited with errors. Also, this is from last years WWDC, which is fine no? — daihovey, Jun 12 '12 at 09:58
I guess it should be fine though i remember seing disclamer somewhere. — Rok Jarc, Jun 12 '12 at 10:11

score 15 · Accepted Answer · answered Jun 12 '12 at 10:11

15

School boy mistake.

Didn't add #import <ImageIO/ImageIO.h>

answered Jun 12 '12 at 10:11

daihovey

3,485
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score 3 · Answer 2 · edited May 23 '17 at 12:30

Try image 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;
}

i use it in my code for awhile but i can't remember it's source

try this also resizing a UIImage without loading it entirely into memory?

Thanks for this, but I specifically wanted to use the `CGImageSourceCreateThumbnailAtIndex` function — daihovey, Jun 12 '12 at 10:01
http://stackoverflow.com/questions/5860215/resizing-a-uiimage-without-loading-it-entirely-into-memory try this please — Mina Nabil, Jun 12 '12 at 10:03

CoreGraphics Image resize

2 Answers2

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