It's possible there is some more simple way that I don't know about, but I imagine you will have to create a script or batch file which tests file type (extension) and invokes the wanted program based on that test. Then assign F4 to the script or batch file.
I just threw this batch file together in a hurry but it seems to do what you want. You will need to change the path to where the Photoshop is in your computer, and also set the full path to EditPlus (I used the standard Windows Notepad to test).
[code]@echo off
:: Enter image file extensions separated by a space
:: Note the file extensions ARE case sensitive!
set IMGS=.psd .PSD .jpg .JPG .gif .GIF .png .PNG .bmp .BMP .tif .TIF
:: Full path to Photoshop
set P=C:\Program Files\Adobe\Adobe Photoshop CS3\Photoshop.exe
:: Full path to EditPlus
set E=C:\WINDOWS\system32\notepad.exe
for %%A in (%IMGS%) do (
if "%~x1" == "%%A" (
"%P%" "%~1"
set T=on
exit
)
)
if not defined T "%E%" "%~1"[/code]
You can add or delete image types as desired, but note the file extension types are case sensitive because I'm using the FOR iterator command in the script. To use this script save it with a name you like (in my test, I called it test.cmd) and call it with an Opus button command something like this: