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    <p>Are you asking how to create thumbnails from larger images, or about how to build a view controller which displays them nicely?</p> <p><strong>Building a view controller:</strong></p> <p>You could use <code>TTPhotoViewController</code> from <a href="http://github.com/joehewitt/three20/tree/master" rel="nofollow noreferrer">the Three20 project</a> (<a href="http://joehewitt.com/post/the-three20-project/" rel="nofollow noreferrer">description</a>), which acts similarly to the iPhone's built in camera roll to view images.</p> <p>You can look at <a href="https://developer.apple.com/iphone/library/samplecode/Scrolling/index.html" rel="nofollow noreferrer">the <code>Scrolling</code> sample code</a> from apple, referred to in <a href="https://stackoverflow.com/questions/652644/better-way-to-have-a-photo-slider-thumbnails-on-iphone">this question about using it for thumbnails</a>.</p> <p>If you want to build one yourself, you might consider using a <a href="http://bynomial.com/moriarty/GridView.h.txt" rel="nofollow noreferrer"><code>GridView</code></a> from <a href="http://bynomial.com/moriarty/" rel="nofollow noreferrer">the moriarty library</a>, either as a large grid in a <code>UIScrollView</code>, or on a more efficient row-by-row basis in a <code>UITableView</code>. There's a previous question on <a href="https://stackoverflow.com/questions/1098234/optimized-image-loading-in-a-uiscrollview">optimized image loading in a <code>UIScrollView</code></a>.</p> <p><strong>Creating thumbnails from larger images:</strong></p> <p>The code-easiest way to scale down an image is to simply display it in a <code>UIImageView</code> with a frame set to the smaller size that you want - it's scaled for you.</p> <p>If you want to save a thumbnail, or care about memory usage, you can create a hard-scaled version. The sample code below is taken from <a href="http://ofcodeandmen.poltras.com/2008/10/30/undocumented-uiimage-resizing/" rel="nofollow noreferrer">this blog post</a>, and can be added to <code>UIImage</code> as a category method:</p> <pre><code>- (UIImage*) imageScaledToSize: (CGSize) newSize { UIGraphicsBeginImageContext(newSize); [self drawInRect:CGRectMake(0, 0, newSize.width, newSize.height)]; UIImage* newImage = UIGraphicsGetImageFromCurrentImageContext(); UIGraphicsEndImageContext(); return newImage; } </code></pre> <p>Finally, here's a previous question on <a href="https://stackoverflow.com/questions/996292/how-to-mask-a-square-image-into-an-image-with-round-corners-in-the-iphone-sdk">masking out round corners on an image</a>, similar to the app icons used on the home screen.</p> <p><em>Added</em></p> <p><strong>Using an image's built-in thumbnail:</strong></p> <p>There's a nice function called <code>CGImageSourceCreateThumbnailAtIndex</code> that understands built-in thumbnails in certain image data formats. You can see some useful sample code for this under <em>Creating a Thumbnail Image from an Image Source</em> in <a href="http://developer.apple.com/library/mac/#documentation/GraphicsImaging/Conceptual/ImageIOGuide/imageio_source/ikpg_source.html#//apple_ref/doc/uid/TP40005462-CH218-DontLinkElementID_5" rel="nofollow noreferrer">the Image I/O Programming Guide</a> from Apple.</p>
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    1. POThumbnail view of images
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    1. COamazing! it is great!
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    2. COThis does not maintain even a little bit of aspect ratio of the image.
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    3. CO@Shailesh, by specifying the newSize of the image, the resulting aspect ratio is completely up to you. You can preserve the old aspect ratio, for example, by choosing a float "scale" so that oldSize.width * scale and oldSize.height * scale both fit into the room available for the thumbnail, and then effectively setting newSize = oldSize * scale.
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