BMP to PNG

May 17, 2009 1:20 PM

Looking for a free Windows program that will batch convert a bunch of BMPs to PNGs without making the colors darker.

I have a couple hundred BMP files I would like to convert to PNG. The problem is, all I've found are programs that either cost money, or ruin the colors (the outputted PNGs wind up being darker than the BMPs). I never encounter this problem when saving PNGs with GIMP (which is the program I generally save my PNGs in -- I don't think GIMP can do batch conversions, though). I've also tried IrfanView, but I encounter the same dark PNG problem.

I'm looking for a program that will run in Windows XP (Windows command prompt programs are fine), is free, can do batch conversions, and won't screw with the colors. Any suggestions?

posted by Dreamcast to computers & internet (8 comments total)

The standard open-source (cross-platform) command-line imaging program is ImageMagick. Incredibly versatile, incredibly powerful, incredibly fast. It's useful for all kinds of things, but batch conversion/manipulation (everything from making thumbnails to changing the lighting in exactly the same way on 2,000 photographs) is where it shines.

But, just so you know: GIMP can do batch conversions. It's actually quite simple.
posted by koeselitz at 1:26 PM on May 17 [3 favorites has favorites]

Did you search SourceForge?

http://sourceforge.net/search/?type_of_search=soft&words=batch+convert+bmp+png
 
posted by querty at 1:44 PM on May 17

I'm not so sure that your problem in color change is in the conversion. It may be in whatever you're using to view the images afterwards. Some earlier programs (and some versions of some browsers) did strange things in displaying PNGs because they applied a weird gamma correction before display, which they didn't do for JPG or BMP.

I know that was a problem in some older versions of Opera, for example.

How are you viewing the images?
posted by Chocolate Pickle at 1:45 PM on May 17

I'd like to suggest a test: convert a BMP to PNG using your current tool, and then convert it back to BMP and see if the color shift is maintained. I bet it isn't; I bet the resulting BMP will look exactly the same as the original.
posted by Chocolate Pickle at 1:46 PM on May 17

BMPs don't contain any color profile or gamma information, IIRC, so presumably all you need to do is have a gAMA chunk in the PNG to tell the program displaying it to act as if it's being displayed on an old Windows system (instead of using whatever standardized or default curves it's using). Or perhaps whatever you're using to view the BMPs is displaying them too light, and the PNGs are the correct (even if undesired) representation.
posted by hattifattener at 1:59 PM on May 17

Have you tried the program: Format Factory?

It converts video, audio, and images into various formats.
posted by royalsong at 2:08 PM on May 17

For Windows? IrFanView.
posted by ostranenie at 7:19 PM on May 17

I'm gonna plug FastStone again (second time this week! I've no affiliation, just like their apps) because, seriously, their tools are awesome. FastStone Photo Resizer or Image Viewer will do batch image conversions for you. Both apps are quick, easy to use, and free.
posted by LuckySeven~ at 8:33 PM on May 17