How to use GPUImageLookupFilter without GPUImageFilterGroup?

Question

I have a problem with understanding GPUImage. Specifically, I can't figure out how to use GPUImageLookupFilter. I have several examples of usage in GPUImageAmatorkaFilter for example. But LookupFilter used there within GPUImageFilterGroup which I didn't understood yet either. I wonder whether I can use LookupFilter alone.

I've tried this:

GPUImageLookupFilter *lookup = [[GPUImageLookupFilter alloc] init];

UIImage *image = [UIImage imageNamed:@"amatorka.png"];
GPUImagePicture *lookupImageSource = [[GPUImagePicture alloc] initWithImage:image];    
[lookupImageSource addTarget: lookup atTextureLocation: 1];
[lookupImageSource processImage];

GPUImagePicture *inputImg = [[GPUImagePicture alloc] initWithImage:inputImage];
[inputImg addTarget:lookup atTextureLocation: 1];
[inputImg processImage];

UIImage *quickFilteredImage = [lookup imageFromCurrentlyProcessedOutput];

But it doesn't work, it crashes like this:

Assertion failure in -[GPUImageLookupFilter createFilterFBOofSize:], PathToSource/GPUImageFilter.m:369
Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'Incomplete filter FBO: 36054'

I definitely need to initialize something else, but ... . So, can anyone help me to make this small piece of code work? Thanks in advance.

Answer 1

Thanks to Brad Larson for answering:

For one thing, you're adding both of your images to texture location 1, so one is overriding the other. You need to add your input image to texture location 0 and lookup pattern to location 1, I believe.

Answer 2

This is how I personally use it:

- (UIImage *)filterImage:(GPUImagePicture *)originalImageSource withLUTNamed:(NSString *)lutName
{
    GPUImagePicture *lookupImageSource = [[GPUImagePicture alloc] initWithImage:[UIImage imageNamed:lutName]];
    GPUImageLookupFilter *lookupFilter = [[GPUImageLookupFilter alloc] init];

    [originalImageSource addTarget:lookupFilter];
    [lookupImageSource addTarget:lookupFilter];

    [lookupFilter useNextFrameForImageCapture];
    [originalImageSource processImage];
    [lookupImageSource processImage];

    return [lookupFilter imageFromCurrentFramebufferWithOrientation:UIImageOrientationUp];
}