Save rendered image before compositing without re-rendering I have rendered an image. It took a long time to render it.

I also have compositing nodes. For clarity let's call the image after rendering "image A", and the final image after compositing "image B". I would like to tweak the compositing nodes without re-rendering. Now I can do it, because Blender is still running, but if I close and start Blender, image A will disappear, and I have to render again. 

So I would like to save Image A now (in openexr multilayer format, with all the render passes), so that the next time I can put it into an Image input node, and tweak the compositing nodes without re-rendering. 

I can save image B from the UV/Image Editor with F3, but I found no way to save image A - although it is still in Blender now. How can I do it?
OK, I found it in the meantime. The EXR file of image B actually also contains image A, I just have to switch the "Layer" in the Image input node. I hope in the future this question and answer will still help somebody.