On 18 Mar 2014, at 14:22, Jim Crate <j...@quevivadev.net> wrote:
>
> I would start with something like this:
>
> CIImage *img = [CIImage emptyImage];
> for … {
> // calculate tile position from index, create NSAffineTransform for
> scaling/translating
> CGImageRef tileRef = // get image from AV framework
> CIImage *tile = [CIImage imageWithCGImage:tileRef];
>
> CIFilter *f = [CIFilter filterWithName:@"CIAffineTransform"];
> [f setValue:transform forKey:kCIInputTransformKey];
> [f setValue:tile forKey:kCIInputImageKey];
> tile = [f valueForKey:kCIOutputImageKey];
>
> CIFilter *f = [CIFilter filterWithName:@"CISourceOverCompositing"];
> [f setValue:img forKey:kCIInputBackgroundImageKey];
> [f setValue:tile forKey:kCIInputImageKey];
> img = [f valueForKey:kCIOutputImageKey];
>
> // you’ll need to figure out whether it is safe to CGImageRelease your
> grabbed CGImageRef here
> // or if you need to keep track of them and release them at the end of
> the process
> }
>
> // you’ll have to figure out your colorspace and bitmap info
> CGColorSpaceRef colorSpace = CGImageGetColorSpace(imgRef);
> CGBitmapInfo bitmapInfo = CGImageGetAlphaInfo(imgRef);
> CGContextRef cgContext = CGBitmapContextCreate(NULL, destRect.size.width,
> destRect.size.height, 8, 0, colorSpace, bitmapInfo);
>
> CIContext *ciContext = [CIContext contextWithCGContext:cgContext options:nil];
> CGImageRef tiledImageRef = [ciContext createCGImage:img fromRect:[img
> extent]];
>
> // save the image using ImageIO
> CGImageDestinationRef destRef = CGImageDestinationCreateWithURL((__bridge
> CFURLRef)destURL, (__bridge CFStringRef)imageType, 1, NULL);
> CGImageDestinationSetProperties(destRef, (__bridge CFDictionaryRef)propsDict);
> CGImageDestinationAddImage(destRef, tiledImageRef, (__bridge
> CFDictionaryRef)propsDict);
> CGImageDestinationFinalize(destRef);
>
> CGImageRelease(imageRef);
> CFRelease(destRef);
>
>
> If you wanted better thumbnail image quality, you could use the Lanczos
> filter first, then just use the NSAffineTransform to translate the picture to
> the proper tile position. Also, I see there is an imageByApplyingTransform
> method that takes a CGAffineTransform, so it may be even simpler if you’d
> rather use that.
I felt the need to give this a go and I've produced a little command line tool
that tests this out. I've also provided some performance results for a few
options. I've gone for the CILanczosTransform filter, I don't know if that
slows things down, a quick look at the profile results didn't appear to show
that any one area dominated overly so I've not done anything to try and
optimize but at the same time I'm not that impressed with the speed.
I was also going to try and include an option for the command line to select
creating the coversheets using coregraphics and gcd to achieve concurrency but
the more I thought about the harder it seemed to integrate the two different
approaches into 1 tool. I'm going to try write a new tool to do that. Perhaps
once I've finished it I'll better be able to see how both approaches can be
integrated.
The information including code etc. you can view at the git hub repository
where I've saved stuff.
https://github.com/SheffieldKevin/makecoversheet
Kevin
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