Image Transform use linear or nearest sampling during editing and exporting. This gets sampling is fine for images that aren't scaled. When sequencing however you mostly want use some sort of scaling, that leads to poorer quality. This change will use sub-sampling to improve the quality. This is only enabled when rendering. During editing the subsampling is disabled to keep the user interface reacting as expected. Another improvement is that image transform is stopped at the moment it hadn't sampled at least 4 samples for a scan line. In that case we expect that there are no further samples that would change to result. In a future patch this could be replaced by a ray/bounding bo intersection as that would remove some unneeded loops in both the single sampled and sub sampled approach.