Reply to thread

1/ When you move layers around, or when you put images on layers that are bigger that your background (or the size you want your definitive image to be), the unseen information is hidden, but still available. This uses up unnecessary memory. You can delete this info by Ctrl+A (select all) and then Image>Crop.

2/ Sometimes you may need to duplicate a layer with the intent to use the blending modes. This doubles the file size of this layer. You can also make use of an adjustment layer, for example Levels, change none of the settings and blend this with your layer. This can save you megabytes of memory.

If you're not very familiar with adjustment layers, know that they're just like Image>Adjust, but with some extra possibilities.

For example: the changes are not permanent, and can be applied to more than one layer at the time. You find them in the Layers menu, and also in the third icon from the right at the bottom of the layers palette.