On 17 Aug 2010, at 18:05, Ken Ferry wrote:
>
> (1) I would focus your attention on CoreImage in this case.
> (2) It is wonderful that you realized that if you want the bits in a specific
> pixel format then you need to draw them in a bitmap, but you now have a
> redundant bitmap:
Yes, I wanted to be sure I knew exactly what my bitmap format looked
like. And yes again, I realised there was some redundancy there - I
wasn't quite sure at the time I wrote it how to avoid that.
> You can directly draw the CIImage in the context created from the bitmap.
>
> This by itself is not likely to be your problem, but fixing this may have a
> side effect that fixes the problem. When you use -[NSBitmapImageRep
> initWithCIImage:], it basically calls -[CIContext createCGImage:fromRect:]
> using -[NSGraphicsContext CIContext]. The latter is possibly a long lived
> object, and the CIContext may be the location of caches.
I think we're on the right track. I've cut out the redundant bitmap and
although the problem remains, it's noticeably reduced. (One of my test
sets contained 3500 images - previously it would chew through all 8GB,
but with my replacement code I have over 2.5GB left with no extra swap
files. This isn't good enough, but it's a good start.)
My bitmap code now looks like this:
NSInteger pixelsWide = [ciImage extent].size.width;
NSInteger pixelsHigh = [ciImage extent].size.height;
NSInteger samplesPerPixel = 4;
NSBitmapImageRep *bmpImgRep = [[[NSBitmapImageRep alloc]
initWithBitmapDataPlanes:NULL
pixelsWide:pixelsWide pixelsHigh:pixelsHigh
bitsPerSample:8
samplesPerPixel:samplesPerPixel hasAlpha:YES
isPlanar:NO
colorSpaceName:NSCalibratedRGBColorSpace
bitmapFormat:0
bytesPerRow:0 bitsPerPixel:0] autorelease];
[NSGraphicsContext saveGraphicsState];
NSGraphicsContext *ctx = [NSGraphicsContext
graphicsContextWithBitmapImageRep:bmpImgRep];
[NSGraphicsContext setCurrentContext:ctx];
[[ctx CIContext] drawImage:ciImage atPoint:NSMakePoint(0,0)
fromRect:NSMakeRect(0,0,pixelsWide,pixelsHigh)];
[NSGraphicsContext restoreGraphicsState];
The documentation for -[NSGraphicsContext CIContext] says that the CIContext
only lives for as long as its owning NSGraphicsContext, so I'm assuming (!) that
it'll be released when I pop the owning context with -restoreGraphicsState.
> (Also, it's unlikely that you want device RGB as the colorspace for the
> bitmap. If you want your results to be independent of the machine they're
> produced on, you need to be using device-independent colorspaces.)
You're right - that was sloppy cut-and-paste on my part. I'm a bit hazy
on colour spaces, but I've switched it to NSCalibratedRGBColorSpace.
Thanks very much for your help, it's much appreciated.
Stuart
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