Send me a short sample project with PNG where this problem may occur. I will check its memory usage.
Being a 32-bit app, PTE 9 can use only up to 2 GB of system memory. With a special trick we can extend this limit up to 3.9 GB.
6000 x 4000 PNG image takes 96 MB - width x height x 4 bytes (RGBA). 1 copy of image in PTE, 1 copy in system memory of Direct3D engine, and 1 copy in a video memory (all these copies share common address space of 2 GB). In total we have 288 MB just for one 6000 x 4000 image. PTE uses 1 player in the main window (preview area), 1 player for the Slide list, 1 player in the editor of animations. The editor loads only one current slide. The preview player in the main window loads 3 slides in advance (with all their images).
Of course, we use several tricks to economy memory, for example, we calculate current size of a preview player/ or in a EXE and proportionally downsize PNG/JPEG images before loading. The most effectively it works for JPEG. JPEG format allows to load already downsized copy of an image if we need to show a small copy of an image (it saves times of loading and memory usage). For PNG we have to load a full size copy and then downsize it before pass to a video card or DirectX.
So only 64-bit version of PTE may help improve this situation. And PTE will able to use all memory of your computer. And we're working on 64-bit version of PTE right now.
With 64-bit app out of memory problem should not occur, because all moderns computers have at least 8-16 GB of system memory.
P.S. All 3D games load textures (images) in a lossy format (something like JPEG with a strong compression), it reduced memory usage in 2-4 times. PTE loads images to textures in a video card using lossless format (RGBA) providing original image quality.