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mixing Cocoa and QuartzComposer : is there a performance hit using NSImage ?

Hello,

==== The context ====
I want to make a little Cocoa application that makes some image processing with a regular C code. My cocoa code would be connected to two quartz compositions to delegate most of the code.
The first QC would be a simple "Video Input" patch, allowing me to
1)display what my webcam sees in a QCView
2)allows me to capture frames programmatically with some "valueForOutputKey" on the composition
The second QC is some image processing with CIKernel, so it is attached to a QCrenderer to perform that offscreen.
My data flow is planned to be :
Video Input running in a QCView => valueForOutputKey: regularly => I get an NSImage => I process it using regular C code (offscreen) => I inject the result in another Quartz composition using setValue:forInputKey => some additional processing is performed offscreen => I get a final result that I can display

==== My questions ====
In the documentation of QuartzComposer, I have learnt that image ports can receive NSImage or CIImage and make conversions on the fly if it is necessary. Indeed, with the "valueForOutputKey:" I get an NSImage, and when I use "setValue:forInputkey:", I inject an NSImage where a CIImage is needed, but it works well.
However, in my data flow, I expect a decent frame rate, and I am afraid that NSImage would hit the performances.
1)I can only get an NSImage from a "valueForOutputKey:". Is there no way to get a CIImage instead ?
2)Is there a performance hit using NSImage, or is the internal NSCIImageRep highly optimized in this case ?
3)My tests have shown that it performs rather well. But am I doing wrong anyway, is there a better way to do ?

Regards,

Pierre Chatelier

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