Bash: How to convert whatever size pnm file to a jpg of a fixe size of 2.0mb ?

Is this homework ? What purpose could this serve, other than to amuse a teacher.

From frenchnoob---I don't think so. But you got the real question right: Why??

I think that the intent here is to convert format and make the file smaller. I was surprised to find out that you can specify the target pixel count.....

http://www.imagemagick.org/Usage/resize/#resize

My simple mind continues to be boggled by what ImageMagick can do.

H_TeXMeX_H was right ...
Frenchn00b is a geek, real one, that talks badly english..
even he's making progresses in linux with trying hard all kind of things with linux.

So I found those ways:
- convert/imagemagick
man convert
gives -resize geometry
but we can screw up the shapes of the pic
beware because it can after the quality of the pic... not so perfect always... still fighting
... still looking

well wont be easy to calculate the ratio of reduction, ...

pffff

79MB x 50 /100 = 2.3 Mb

I think I see what you are trying to do now, you're trying to scale down a picture to be under 2 MB right ? or does it have to be exactly 2 MB in size ?

Indeed you would need to try to calculate the size of the file with respect to the pixel count. So, take several files and see what size they have, then divide it by the pixel count = width x height. You'll get an estimate of bytes per pixel ... I'm not sure how jpeg compression works, but this may not be the same for every picture. It may just turn out to be 24 or 32, who knows.