(Edit: I see you already had located
Falko's Modding Tools. I'll place my previous message about it inside a 'spoiler' window to get it out of the way.)
Spoiler:
You may find this tool helpful.
Falko created a collection of programs for modding OpenXcom:
https://openxcom.org/forum/index.php/topic,2980.0.htmlOne of them corrects images to be in the correct format for running with either
X-COM: UFO Defense or
X-COM: Terror From The Deep.
OXC-ModTools Palette converter:
https://falkooxc2.pythonanywhere.com/spritepaletteYou don't need to download anything it works right off the website.
Try running your image through that program and see if it helps.
If it doesn't work or removes the background transparency try both the '
fix-palette(ufo-battlescape)' setting and the '
set-palette(ufo-battlescape)' setting.
To use the program:
(1) Click the "Drop files here or Click to upload multiple images" button.
(2) Select your images.
(3) If needed choose your palette.
(4) Press "Convert".
(5) Press "Download" to gain access to the converted file.
With large sprite sheets it can take a moment or two to finish after pressing convert, you'll know it is done when the "Download" button isn't faded anymore.
EDIT:* edit: I did find a modding tools website that corrected the image palette, but the background transparency is still there in OXCE.
I've also found that the transparency is lost at times when using
Falko's tool, I'm not sure exactly what causes it.
Using
Falko's tool try clicking '
fix-palette(ufo-battlescape)' setting and changing it to the '
set-palette(ufo-battlescape)' setting instead, sometimes the '
set' option assigns the background as a transparency when the '
fix' option does not.
Another solution I use when this occurs is to add the transparency back into the image using a program like
GIMP then send the corrected image back through
Falko's tool again.
If the background turns
green it has usually worked and the transparency will be intact. (Or
pink if the image is being converted to work with
Terror From The deep.)
Although I'm using it
GIMP is not recommended for creating images for use with
OpenXcom because it can alter the indexed palette unexpectedly. Try one of these instead if you aren't already:
image editors / graphicsIf you attach the image that is giving you trouble to your forum post I'll take a look at it and try to add the transparency if you wish.