No helpful information, but let me join you in sobbing brokenly. Last year I was forced to get a new computer and hence “upgrade” (sarcastic quotes) to the new version of GraphicConverter, which doesn’t have a simple and transparent option for switching to a 16-color (or gray) palette, long my preferred option for monochrome images such as line drawings. I've even looked into an older-OS emulator or VM so I can run my preferred applications, but so far haven't got one to work.

Might help to know what OS you're on. I'm guessing macOS? Since Windows still supports 32-bit applications.

Windows: PNGGauntlet
macOS: ImageOptim
Linux: Trimage

Note that all of these have GUIs and use OptiPNG in the background, along with other optimizers. Maybe not what you're looking for.

Not sure what you mean by "set a transparent background".

@robzilla, it's just Windows 10 Home, version 20H2, OS build 19042.1469. It specifically says "64-bit operatin system, x64-based processor".

I did have Windows 11, but bing bang boom... here I am on Windows 10.

I keep getting mixed information, some saying that 64-bit Win10 stopped supporting 32-bit programs. I'm not sure, all that I really know is that when I downloaded OptiPNG, extracted it, and ran optipng.exe, nothing happened. No errors, but the program didn't open, either.

Not sure what you mean by "set a transparent background".

I used to be able to select a color to make transparent. I usually use PNGs for sprites, and I almost always want them to be transparent.

Not sure what you mean by "set a transparent background".

In full-color mode, transparency is done with an alpha channel. In 256 or less (by definition, this includes any gif) it's done by selecting one color--usually but not necessarily white--to be transparent.

I've been running 32bit programs on 64bit machines since Win 7 ... Have you actually installed and tried running it? Just asking ... I use a different graphics package (32bit) to do what you are describing (not free, a bit more complex than just "converter" stuff).

Aside: My Photoshop 5 still runs under 64bit... which is a bit of a thrill!

OptiPNG runs just fine here on Windows 11 64-bit. You are running it from the command line, right? Seeing as it doesn't have a GUI. Otherwise you might get the idea it's not working :-) Not sure from the help section that it actually supports setting a color to be transparent.

@lucy24, didn't know that!

There are many online services that work well. Just upload to their web form. You can find several by Googling.

You are running it from the command line, right?

No, @robzilla, what I had before had a GUI! Before my old computer died I took a photo of my desktop... the name of it was spelled "OptiPNG" (capitalized like that). The icon is blurrty, but it looks like a sunburst behind it. Maybe I had some other program CALLED OptiPNG that was really just an interface for it?

Hmm.

Aside: My Photoshop 5 still runs under 64bit... which is a bit of a thrill!

@tangor, my favorite was PaintShop Pro 4.12 :-) Back in the day, it was small enough that I kept it on a 3 1/2" disk that I could take to clients and load up!

I just discovered that it will load, too :-D It throws an error at first that it failed up update the system registry (whaa?), but it still loads.

I still have the whole disk set from Adobe... Photoshop 7.0, Illustrator 10, GoLive 6.0, and LiveMotion 2.0, complete with books and everything. Do you want it? It's just collecting dust in my closet...

Maybe I had some other program CALLED OptiPNG that was really just an interface for it?

There are few GUIs for OptiPNG. Looks like you probably had the one called OptiPNG-UI (now discontinued but still available on download sites; I could only get an Italian version though). There's also WOptiPNG on GitHub, and probably others. I like to use PNGGauntlet myself.

You're right, that's the one!

[enzofleri.com...]

I'm super disappointed that it's no longer available :-( I'm going to try one last time to hack in to my old drive, maybe I can salvage it.

I downloaded PNGGauntlet, it looks like it will work fine it's just not as pretty. I'm not seeing an option for transparency, though, is it hidden somewhere? I found "Preserve Gamma Information" under the PNGOUT setting, am I right that this setting would preserve transparency if I've already set it in another program?