maximum image size in CIFilter / CIKernel?

Does anyone know what the limitations are on image size with custom CIFilters? I've created a filter that performs as expected when the images are up to 2 mega pixels but then produce very strange results when the images are larger. I've tested this both in my cocoa app as well as in quartz composer. The filter I've developed is a geometry-type distortion filter that (I think) requires an ROI and a DOD that spans the entire input image. I've created this filter for remapping panoramic images so I'd like this to work on very large (50-100 mega pixel) images.

As a simple test the consider the following CIFilter (can be used in Quartz Composer) that simply translates the image so that the lower-left corner of the images is translated to the center (I know this could be done with an affine transform but I need to perform such an operation in a more complex filter). This filter works as expected when the image is 2000x1000 but produces odd results when the input image is 4000x2000 pixels. The problem is that either the translation does not move the corner to the center exactly or that the image output is gone entirely. I've noticed other odd problems with more complicated filters on large images but I think this simple filter illustrates my issue and can be replicated in Quartz Composer.

kernel vec4 equidistantProjection(sampler src, __color color)
{
vec2 coordinate = samplerCoord(src);
vec2 result;
vec4 outputImage;

result.x = (coordinate.x - samplerSize(src).x / 2.0);
result.y = (coordinate.y - samplerSize(src).y / 2.0);

outputImage = unpremultiply(sample(src,result));

return premultiply(outputImage);
}

The same odd behavior appears when using the working coordinates instead of the sampler coordinates but in this case the error occurs for images of size 2000x1000 but works fine for images of size 1000x500

kernel vec4 equidistantProjection(sampler src, __color color, vec2 destinationDimensions)
{
vec2 coordinate = destCoord();
vec2 result;
vec4 outputImage;

result.x = (coordinate.x - destinationDimensions.x / 2.0);
result.y = (coordinate.y - destinationDimensions.y / 2.0);

outputImage = unpremultiply(sample(src,result));
outputImage = unpremultiply(sample(src,samplerTransform(src, result)));

return premultiply(outputImage);
}

For reference I have added to the Objective-C portion of my filter's - (CIImage *)outputImage method the following to set the DOD to be the entire input image.

- (CIImage *)outputImage
{
CISampler *src = [CISampler samplerWithImage: inputImage];



NSArray * outputExtent = [NSArray arrayWithObjects:
[NSNumber numberWithInt:0],
[NSNumber numberWithInt:0],
[NSNumber numberWithFloat:[inputImage extent].size.width],
[NSNumber numberWithFloat:[inputImage extent].size.height],nil];


return [self apply: filterKernel, src, inputColor, zoom, viewBounds, inputOrigin,
kCIApplyOptionDefinition, [src definition], kCIApplyOptionExtent, outputExtent, nil];

}

Additionally I added the following method to set the ROI which I call in my - (id)init method with this: [filterKernel setROISelectorselector(regionOf:destRect:userInfo];

- (CGRect) regionOfint)samplerIndex destRectCGRect)r userInfobj
{

return r;
}

Any help or advice on this issue would be greatly appreciated. I'm sure that CIFilters can work with larger images as I've used the CIBumpDistortion with greater than 50 megapixel images so I must be doing something wrong. Any ideas?

 

No luck getting it working yet. I tested on a mac pro too (I work mostly on a MBP) to make sure that it wasn't just my machine and it fails in the same way. I'm beginning to wonder if I need code this up using openCL and move away from the CIFilters (they're just so darn convenient to use!).

The "size" thing is actually more of an openGL thing than an Apple thing. samplerSize returns a vec2 which has components .x and .y.

I did some experiments to try and figure out whats going on and it seems that when an image reaches a certain size that the values returned from samplerSize become a multiple of 2. I managed to find away to predict how this works but then my method breaks once I add more to the CIKernel's algorithm. Frustrating. There should be some documentation about this somewhere but I can't find any.

I wish I could output to the console from within a CIKernel as it would make debugging much easier.

I'll wait a while before committing to reworking this in openCL and see if anyone else has some ideas.

Thanks!

 

Ask and you shall receive! I've uploaded a very simple app that illustrates this problem. Build and run the app and open an image file from: file: open: to see this is action. If the image is sufficiently small you should see the image in the view translated so that the lower left corner of the image has been moved to the center of the view. For larger images the translation becomes weird. You can resize the window / view and see how the weirdness changes.

Thanks in advance for any input you might have!

 

I too have had the same issues with using destCoord(). Do you know if there is a way to know how it tiles and what to do with the tiles?

 

Thats what I was afraid of. Looks like it might be time to bit the bullet and learn to code the filters I need up in openCL. I guess I shouldn't have expected to be able to take the easy road.

 

Well I'm thinking now that I'll just scale down the image appropriately for display to the screen and only worry about using the large images when saving to disk. Is there a way to tell core image to process the CIImage through the CIKernels using the CPU instead of the GPU? I would think so since it's designed to have the CPU as a backup but I can't find any info on how to do it.