BMP files don't have compression. The file size in bytes is the total number of pixels multiplied by the color depth (in bytes).
So for example, 1024x768 with 8bit color is a 768KB file. 1024 x 768 x (1 byte)

640x480 256 color .BMP files used to be common, those work out to 300KB each.
High res images with more color get very inefficient without compression. 1600x1200 24bpp is about 5.5MB.

I'm not much of a picture editing person, but any paint program I've ever used has supported saving to BMP files. MS Paint is simple but very limited. I like Paint Shop Pro 4, but it won't satisfy every need. Irfanview is a more modern option than those, but I haven't used it for painting pixels much. Photoshop, Gimp, etc are complicated but if you know how to use them, they can do the most.

My 1993-94 preferred BMP program was Paint Shop Pro, including from before it became a Zsoft-inspired paint program at v3. It had decent processes for converting color depth as well

In terms of Win3.x gfx software, I also remember WinGIF, Graphic Workshop, Easel, etc.
Standard resolution was 640x480 pels, in either 16 or 256 colours.

Another form of BMP, called RLE, used some form of compression (run-lenght enconding).
https://docs.microsoft.com/en-us/windows/desk … map-compression

Last but not least, there also was WMF, the Windows Metafile Format.
https://en.wikipedia.org/wiki/Windows_Metafile

Edit: Also have a quick look what the Wiki says about the Windows system palette.
Especially "In 256-color mode, there are four additional standard Windows colors, twenty system reserved colors in total;
thus the system leaves 236 palette indexes free for applications to use."
https://en.wikipedia.org/wiki/List_of_softwar … 0-color_palette

Jo22 wrote:

Another form of BMP, called RLE, used some form of compression (run-lenght enconding).
https://docs.microsoft.com/en-us/windows/desk … map-compression

True, RLE formats are still fast to decode on old systems and can significantly cut down on file sizes if the images are hand drawn graphics (not photographs that change color every pixel).
I don't remember if Windows 3.x has any support for displaying them on the desktop though.

Edit: Also have a quick look what the Wiki says about the Windows system palette. Especially "In 256-color mode, there are four […]
Show full quote

Edit: Also have a quick look what the Wiki says about the Windows system palette.
Especially "In 256-color mode, there are four additional standard Windows colors, twenty system reserved colors in total;
thus the system leaves 236 palette indexes free for applications to use."
https://en.wikipedia.org/wiki/List_of_softwar … 0-color_palette

It's been a long time since I used it, but I remember Paint Shop Pro having an option related to this. When scaling the color depth to 8bpp, I think it had an option for whether or not to interfere with the reserved portion of the palette. So that's one point in favor of PSP.
If you don't have need for really advanced features like Photoshop, then Paint Shop Pro would be my recommendation. PSP is simple enough but capable enough to hit a good sweet spot IMO.

shamino wrote:

Jo22 wrote:

Another form of BMP, called RLE, used some form of compression (run-lenght enconding).
https://docs.microsoft.com/en-us/windows/desk … map-compression

True, RLE formats are still fast to decode on old systems and can significantly cut down on file sizes if the images are hand drawn graphics (not photographs that change color every pixel).
I don't remember if Windows 3.x has any support for displaying them on the desktop though.

I don't, either. WinGIF supported it, at least (just checked). 😀

Edit: Screen capture added.

Now that I think about it, I remember a few more picture programs for Win3.x.
PhotoStacker Plus, iPhoto and ImagePals.

These weren't exactly popular, so I hope you don't mind if I add some pictures of them.
PhotoStacker Plus was interesting, since it supported a uniqe form of JPEG no other program supports (DPCM lossless).
It also can read more exotic file types, such as GEM and MSP (ancient Windows picture format).

I use Adobe Photoshop 4.0 for Windows 3.x screenshots but it requires Win32

PS for Windows 3.1 is cool. Version 5.x also introduced that special brush/feather, or was it 4 already ?

Anyway, I also remember that CorelDRAW was popular, too.

IrfanView and XnView could run on Win32s, too.

Last XnView for 3.x was v1.50, I believe. 😀