On Aug 20, 2013, at 18:02 , Uli Kusterer <witness.of.teacht...@gmx.net> wrote:
> On Aug 20, 2013, at 12:36 PM, Gerriet M. Denkmann <gerr...@mdenkmann.de> > wrote: >> Well that much I know. And I also know that many NS/UI-things (which use >> Objective-C) often have a CF-counterpart, which uses plain C and often these >> are toll-free bridged. The latter kind is typically used when one needs more >> options or finer control. (E.g. NSDictionary / CFDictionary). >> >> But what is the story behind NS/UIView relative to CIImage, CGImage? When to >> use what? What are the relevant advantages? >> >> I would really like to get some link to some documentation, which explains >> these questions. > > > NSImage/UIImage: Highest-level image abstraction, usually independent of > pixels (e.g. may hold vector graphics, values are measured in Points, not > pixels) > CGImage: Highest-level pixel-based representation of an image, mostly > measured in actual pixels, you have to do all Retina-work yourself. > CIImage: Abstraction on top of textures on a graphics card for use as images. > Useful if you want to quickly apply effects (CIFilter, transitions etc.) to > an image, because the image is kept in GPU memory instead of RAM, so for > applying several filters you save repeated up/downloads, and the filters run > on many cores on the GPU, instead of blocking the few CPU cores your phone > has. > > Note that the abstraction is transparent. E.g. for bitmap images, NSImage > these days uses a CGImageRef under the hood. Also, CGImageRefs try to be > smart about keeping image data on the GPU if they can (so conceptually "use > CIImage", if not actually). NSImage: a container format for multiple representations of an image for optimized display. Can contain different image representations (NSImageReps), for example a PDF and bitmaps at multiple resolutions, and will create additional cached representation(s) if the display and the available representations don’t match, for example rasterizing a PDF for you and then using that rasterized representation for you. Can result in odd behavior, for example scaling the the cached bitmap instead of re-rasterizing the PDF or even using the cached bitmap when printing (yikes!). If you want control, don’t use this (devs have been learning this lesson over and over since early NeXTStep days). I think of it as the NSIcon class. (Note: since 10.6 there has been some access to the selection mechanism with bestRepresentationForRect:context:hints:) UIImage / NSBitmapImageRep / CGImage: a bitmap in UIKit, AppKit and CoreGraphics, respectively Both UIImage and NSBitmapImageRep wrap a CGImage(Ref) (UIImage always did, with NSBitmapImageRep this happened a while ago, I think in Leopard). To the best of my knowledge, UIImage is equivalent to NSBitmapImageRep, not NSImage, because it does not allow vector data. Due to the history of NSBitmapImageRep, it does have methods for direct access to the bitmap data, but because it is now a wrapper for CGImageRef, using those tends to be somewhat inefficient, requiring sending the bitmap data back and forth between graphics card and main memory. IIRC, the recommended way of getting the color at a pixel is to create a context and draw the image into the context with appropriate clipping. That way, the extraction can be done on the graphics card and only the result shipped back to the CPU. In UIImage, they dropped support for the direct access methods. CIImage: for CoreImage, a virtual image "Although a CIImage object has image data associated with it, it is not an image. You can think of a CIImageobject as an image “recipe.” A CIImage object has all the information necessary to produce an image, but Core Image doesn’t actually render an image until it is told to do so. This “lazy evaluation” method allows Core Image to operate as efficiently as possible.” The recipe is executed if you draw the CIImage on a context or initialize another type of image with it. I personally know very little about CIImage, have only used it a couple of times. Are there interesting uses for this outside of CoreImage? Marcel _______________________________________________ Cocoa-dev mailing list (Cocoa-dev@lists.apple.com) Please do not post admin requests or moderator comments to the list. Contact the moderators at cocoa-dev-admins(at)lists.apple.com Help/Unsubscribe/Update your Subscription: https://lists.apple.com/mailman/options/cocoa-dev/archive%40mail-archive.com This email sent to arch...@mail-archive.com
