This might be more of a photoshop/general image file question. But I’ve started using a third party windows explorer (XYplorer) and noticed only in the preview that with an image I rendered out that has a window with transparency, it actually shows the window as if it were just a reflective/glossy surface. But then when it was rendered, and when I open it in photoshop, that space is just transparent, as I would have normally assumed.
But now I’m wondering if blender stores that information in the file anyway, and if there’s a way to access it? Not a big deal, but would be useful in other instances to avoid rendering separate passes for example.
PNG saves transparency if you have the output set as RGBA, and Multilayer EXR saves not only transparency (as an alpha channel), but also different passes for further use in compositing.
To that end: “Multilayer OpenEXR” is specifically designed to be a data-file format, not an image format. Its purpose is the loss-free capture of multiple layers of numbers, exactly as the renderer produced them, so that you can feed them into the next stage of your pipeline. (And yes, the files can be big. So what.) Unlike an image, there is no “correction” or “adjustment” of any kind, and that’s the point. You use them at the final stage to produce an image.