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POCropping a UIImage according to the viewport inside a UIScrollView
 

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  1. POCropping a UIImage according to the viewport inside a UIScrollView
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    <p>I have a UIImageView (initialized with Aspect Fill) inside a UIScrollView. The user shall use that to resize and position a UIImage to his like, press a button and then exactly what he sees on screen would be sent to a server, only in the original image coordinates. In other words, the resulting image would be bigger than the image on screen.</p> <p>Here's the essential part of my code so far:</p> <pre><code>// select the original CGFloat imageRatio = self.imageView.image.size.width / self.imageView.image.size.height; CGFloat viewRatio = self.imageView.frame.size.width / self.imageView.frame.size.height; CGFloat scale; // get the scale factor of the image being "aspect-filled" if(imageRatio &lt; viewRatio) { scale = self.imageView.image.size.width / self.imageView.frame.size.width; } else { scale = self.imageView.image.size.height / self.imageView.frame.size.height; } // get the cropping origin in the image's original coordinates CGFloat originX = self.imageScrollView.contentOffset.x * scale; CGFloat originY = self.imageScrollView.contentOffset.y * scale; CGPoint origin = CGPointMake(originX, originY); // get the cropping size in the image's original coordinates CGFloat width = self.imageView.image.size.width / self.imageScrollView.zoomScale; CGFloat height = self.imageView.image.size.height / self.imageScrollView.zoomScale; CGSize size = CGSizeMake(width, height); // create the new image from the original one CGRect imageRect = CGRectMake(origin.x, origin.y, size.width, size.height); struct CGImage *croppedCGImage = CGImageCreateWithImageInRect(self.imageView.image.CGImage, imageRect); </code></pre> <p>It already looks <strong>quite</strong> close to what I want. The origin calculation at least seems correct. However, there is still some difference in the resulting image, which I guess comes from the different aspect ratios of the possible images. Probably I need to add <code>scale</code> to my <code>size</code> equations somehow, but I seriously just can't wrap my head around <strong>how</strong>.</p> <p>Hopefully somebody can help me get this last two meters...</p> <p><strong>[EDIT]</strong></p> <p>According to the first comment, I tried out the following. But somehow my <code>targetFrame</code> is always identical to <code>scrollFrame</code>. Is it simply too late at night for me to get something right??</p> <pre><code>CGFloat zoom = self.imageScrollView.zoomScale; // the full image resolution CGRect fullImageFrame = CGRectMake(0, 0, self.imageView.image.size.width, self.imageView.image.size.height); UIView *fullImageView = [[[UIView alloc] initWithFrame:fullImageFrame] autorelease]; // the theoretical size of the image on the screen CGRect previewImageFrame = CGRectMake(0, 0, self.imageView.frame.size.width * zoom, self.imageView.frame.size.height * zoom); UIView *previewImageView = [[[UIView alloc] initWithFrame:previewImageFrame] autorelease]; // the excerpt of previewImageFrame really visible CGRect scrollFrame = CGRectMake(self.imageScrollView.contentOffset.x, self.imageScrollView.contentOffset.y, self.imageScrollView.frame.size.width, self.imageScrollView.frame.size.height); // that excerpt transferred to the full resolution image's coordinates CGRect targetFrame = [fullImageView convertRect:scrollFrame fromView:previewImageView]; </code></pre>
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    1. COcould you please post your final solution? I have the same problem
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    2. COI have the same problem, tried similar way, but its never 100% accurate (sometimes the offset of x position is smaller than it should be).
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