Описание тега nsbitmapimagerep
The NSBitmapImageRep class renders an image from bitmap data. Bitmap data formats supported include GIF, JPEG, TIFF, PNG, and various permutations of raw bitmap data.
The NSBitmapImageRep class renders an image from bitmap data. If a coverage (alpha) plane exists, a bitmap’s color components are premultiplied with it. If you modify the contents of the bitmap, you are therefore responsible for premultiplying the data. For this reason, though, if you want to manipulate the actual data, an NSBitmapImageRep object is not recommended for storage. If you need to work with data that is not premultiplied, you should use Quartz, specifically CGImageCreate with kCGImageAlphaLast.
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