I want to convert several thousands greyscale (black and white/monochrome) images in PBM, PNM, TIFF etc to color JPEG / JPG (24 bit) format.

Is there any program / script for batch conversion of image?

I try with convert (imageMagick) but the result are 8 bit Greyscale JPEG images.

How to solve this problem in Linux?
Thank you.

Can it be done? There is no relation between a greyscale and color information, so how can a program possibly do it?

Same for you when you look at a certain B/W photo. Do you know what is blue, red, grey etc? You might see grass and know it's green but it might also have been yellowish when the photo was taken in a dry period.

I assume you want to keep the B/W pictures in gray, but convert the FORMAT to 24-bit JPG. If you want convert gray to lively colors, please refer to WS's answer.

There are many options in ImageMagick, with a description which not always totally clear. I would go for -depth 8 and -color RGB

BTW... some old movies in B/W have been converted to color. They must have started with coloring one picture in a scene, but then what? And did they start the coloring again for each new scene? And the zillions of images in a movie were colored by a computer?

jlinkels