GPUImage capturePhotoAsImageProcessedUpToFilter only working for the last filter

Question

In my application I am using a stack of 3 filters and adding that to a stillCamera. I am trying to take the image from filter1, its an empty filter so it returns the actual image.

    [stillCamera addTarget:filter1];
[filter1 addTarget:filter2];
[filter2 addTarget:filter3];
[filter3 addTarget:cameraView];

When I call capturePhotoAsImageProcessedUpToFilter, it only ever returns an image when I pass it filter3 like below.

[stillCamera capturePhotoAsImageProcessedUpToFilter:filter3 with...

The two examples below never return images

[stillCamera capturePhotoAsImageProcessedUpToFilter:filter1 with...
[stillCamera capturePhotoAsImageProcessedUpToFilter:filter2 with...

Am I doing something wrong? As a fix I am using:

[filter1 imageFromCurrentlyProcessedOutput]

Is there any difference between calling capturePhotoAsImageProcessedUpToFilter and imageFromCurrentlyProcessedOutput?

Answer 1

I think this is a side effect of a memory conservation optimization I tried to put in place last year. For very large images, like photos, what I try to do is destroy the framebuffer that backs each filter as the filtered image progresses through the filter chain. The idea is to try to minimize memory spikes by only having one or two copies of the large image in memory at any point in time.

Unfortunately, that doesn't seem to work as intended much of the time, and because the framebuffers are deleted as the image progresses, only the last filter in the chain ends up having a valid framebuffer to read from. I'm probably going to yank this optimization out at some point in the near future in favor of an internal framebuffer and texture cache, but I'm not sure what can be done in the meantime to read from these intermediary filters in a chain.