Add two layers pixel-wise in Photoshop

Hi!

I'm looking for the simple operation to add two layers pixel-wise for
all channels in Photoshop (ver. 8). I find adjustments layers and
blending options for Multiply, Difference and so on, and I find
Arithmetic's for adding in gray scale and separate channels, but all I
want to do is just to add two layers pixel by pixel for all channels.
That is:
out_image = in_image_1 + in_image_2


I also would like to do the simple operation
out_image = input_image * k + m

I have been searching the net for quite some time, if anyone could give
me a hand here, that would be most appreciated.

regards,
Andreas Lundgren - Sweden

In article .com,
wrote:

Hi!

I'm looking for the simple operation to add two layers pixel-wise for
all channels in Photoshop (ver. 8). I find adjustments layers and
blending options for Multiply, Difference and so on, and I find
Arithmetic's for adding in gray scale and separate channels, but all I
want to do is just to add two layers pixel by pixel for all channels.
That is:
out_image = in_image_1 + in_image_2


I also would like to do the simple operation
out_image = input_image * k + m

I have been searching the net for quite some time, if anyone could give
me a hand here, that would be most appreciated.

regards,
Andreas Lundgren - Sweden

Try posting your question in the comp.graphics.apps.photoshop newsgroup.

Andreas Lundgren writes ...

I'm looking for the simple operation to add two layers pixel-wise
for all channels in Photoshop (ver. 8).
That is: out_image = in_image_1 + in_image_2

You can usually figure out a way to do operations this by getting the
actual formulas for the various blending modes and figuring out how to
apply them. For example, the formula for the "Add" mode is ((source 2
+ source 1)/scale) + offset = destination ... so with scale = 1 and
offset = 0 you'll get what you need ... access this command in
Photoshop CS with Image - Apply Image, the defaults for scale and
offset are already set to 1 and 0 ... this will do the trick.

I also would like to do the simple operation
out_image = input_image * k + m

Did you mean (input_image * k) + m or input_image * (k+m) ? Either way
I think you can figure this out with the blending mode formulas too,
though the straight 'multiply' command is ((source 1) x (source 2))/255
so you may need to combine multiple operations ... if you just multiply
without the divide-by-255 you'll quickly get far too much black ...

I have been searching the net for quite some time, if anyone could
give me a hand here, that would be most appreciated.

Hope this helps ... try to find a list of formulas for the blend modes
(I got mine from the "Photoshop Artistry" books) and realize you might
need to run two operations to get the result you want and it should
make sense.

Bill

if you just multiply
without the divide-by-255 you'll quickly get far too much black

oops, change 'black' to 'white'