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Editorial Team
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Asked: 2026-06-05T13:50:17+00:00

This code is from Apple’s WWDC 2011 Session 318 – iOS Performance in Depth

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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
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1 Answer

  1. Editorial Team

    School boy mistake.

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

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