Background on the Background Layer?

[hartpaul]

I am preparing a lecture tutorial on layers for a camera club group and will be mentioning Background (layer?) , Raster, Vector, Adjustment, Mask and Art Media layers.
I am anticipating a question which will be "What is the purpose of the Background Layer?"
In preparation I looked at PSP8, X2, X3, X4 and X5.

The background layer is like an image attached to a hidden raster layer coloured with the background colour.

You can see this in all versions if you use the selection tool to make a rectangular selection and then hit Delete key.

Also using straighten image with crop unticked, and also the warp brush applied near an edge.

In PSP 8 you could also show the background colour by using a 100% opacity Eraser tool. In all cases the background layer keeps its name.

In later versions using the eraser tool the background is automatically converted to a raster layer.

In the layers palette there is a right click context menu item 'Promote Background Layer'

My question 1. - What is the purpose of having and or keeping a 'Background' layer, does it have any special function that is needed which it cannot serve as a raster layer. For many operations it has to be converted to a raster layer.
As mentioned when using the eraser tool it auto converts to a raster layer.
2. Why not have all images auto converted to a raster layer and so allow the removal of the Promote to Raster layer in the Layers Menu and the Layers context menu.
Or am I missing some esoteric need for the Background Layer

[photodrawken]

The background layer is like an image attached to a hidden raster layer coloured with the background colour.

You can see this in all versions if you use the selection tool to make a rectangular selection and then hit Delete key.

Nope. It doesn't involve a "hidden" layer at all (or a "colored" one). When you delete that selection, the deleted area is simply filled with the current colour specified as the "background" colour in the Materials palette.

PaintShopPro, Photoshop and PhotoShopElements all open an image (with a single layer, such as PNG or JPG) that does not have transparent pixels as having that special "Background" layer, which cannot contain transparent pixels. I don't know why that is, but as you've discovered, creating transparent pixels on it converts the "Background" layer to a normal raster layer (either automatically or manually).

[LeviFiction]

Technically, if a regular raster layer supports transparency it has RGBA (8-bits per value makes a 32-bit image) values. Where as a background layer that does not support transparency would just be RGB (24-bits) which is 8-bits less per pixel. Big question is, does PSP interpret it this way? Or does it assume you'll be wanting transparency at all times.

If PSP does think of it this way then when it first loads images like RAW, JPEG, TIFF and so on then it'll actually take up the least amount of memory until you require other-wise. No point in having transparency if you don't need it.