Pixel info outside image boundaries

["Werner D. Streidt" <wstreidt@bigfoot.de>]

Hi all,

I experimented a bit with coding (mirroring around with src) and I did not
get the results I logically expected. I did not know why!

I don't want to talk about my investigation, so here is the behavior of
FF/FiFo (and probably many other filters) in Photoshop in an example:

Open any image and move the current layer (can be also background layer) 20
pixels to the left and 20 pixels upwards.

One might think that the pixels outside the boundaries are lost.

Yeah, right, apply the following code:

R,G,B,A:
src(x-20,y-20,z,a)

In FiFo:
R=src(x-20,y-20,0);
G=src(x-20,y-20,1);
B=src(x-20,y-20,2);
A=src(x-20,y-20,3);

Huh! The image info is back! :-) Photoshop saves the image info going
outside the boundaries, even when saved to disk and reloaded (of course,only
in .PSD-format)

Can someone test how other host programs deal with their layer management?
Do the experiment explained, maybe the hosts are all equal.

I can't believe no one stumbled across this? Or didn't I read the text
archives? ;-)

Greetings,

Wern