How should I handle hundreds of BMP files in an old archive?

The soundest approach is to separate the folder by content type. Screenshots, scanned documents, interface captures and drawings should go to PNG; genuine photographs can go to JPG if the aim is sharing. Sending everything to the same target may look easier in practice, but converting documents containing text to JPG reduces legibility. Picking a few sample files from the folder and running a test conversion before the batch job lets you spot surprises up front.

Which is right for old scanned documents?

For scanned text documents, PNG is almost always the better choice. JPG compression produces grey shadowing known as ringing around sharp letter edges; this both dirties the document's appearance and reduces accuracy if you intend to run text recognition on it. Because scanned documents usually contain large white areas, PNG's lossless compression works quite efficiently here. If the document consists of many pages and needs to stay whole, consider PDF as a target as well.

Can I convert measurement images produced by an industrial device?

You can, but you have to choose the target carefully. If measurement, counting or automated analysis will be performed on these images, lossy compression is unacceptable; the artefacts JPG produces change pixel values and can affect the analysis result. PNG is the right choice for this kind of content because it preserves pixel values one-to-one. And if there is a workflow where the device or the analysis software still expects BMP, you need to keep the originals as well.

Should I convert old game or CAD asset files?

If you are keeping them purely for archiving or inspection, converting to PNG delivers a serious saving in disk space and costs no data at all. But be careful if the project still builds or a toolchain reads these files; old engines and import tools often expect BMP directly and may not recognise PNG. In that case the safest route is to keep the converted copies in a separate folder and leave the original asset folder untouched.

Converting Legacy Program Output: BMP to PNG or to JPG?

What do you do with a folder full of BMPs?

You opened an old project disk, inherited an institutional archive, or looked into a server folder nobody has touched in years. In front of you are hundreds, maybe thousands of .bmp files taking up an incredible amount of space in total.

The source of these files is usually clear: export output from old Windows software, classic Paint saves, raw output from scanner and fax drivers, recordings from industrial cameras, texture folders from old game and CAD projects, measurement images from laboratory instruments.

The question is: what should you convert them to? This article is a decision guide for people dealing with an archive rather than a single image.

First, let's be clear: conversion is not a rescue operation

There is a common expectation when working with old files: "if I convert it to a modern format it will look better." That does not happen.

BMP is an uncompressed format and stores exactly the data that existed at the moment of saving. A screenshot taken ten years ago at 800x600 will still be 800x600 after conversion to PNG and will look the same. Whatever is in the source is what gets carried across; the conversion adds nothing.

The conversion's real gains fall under two headings: disk space and compatibility. For an archive, those are more than good enough reasons.

The decision: separate by content type

Sending an entire archive to a single target looks easy, but the result is usually a mess, because old folders hold different kinds of content side by side. The right approach is to separate first.

Screenshots and interface captures → PNG

Screenshots taken for old software documentation, bug reports and training material. This kind of content contains large flat colour areas, sharp lines and text.

PNG wins on two fronts here: pixel data is preserved one-to-one, and because flat areas compress very efficiently the file shrinks noticeably. Converting to JPG, by contrast, blurs interface text and often produces a file even bigger than the PNG. Converting BMP to PNG is unarguably the right route for this category.

Scanned documents → PNG

Fax output, scanned contracts, old forms. Anything containing text follows the same logic: JPG compression leaves ringing along letter edges, which both dirties the appearance and reduces accuracy if you intend to run text recognition.

If the document has multiple pages and the pages need to stay whole, it is worth considering PDF instead of PNG.

Measurement and analysis images → PNG

Industrial camera captures, laboratory instrument output, medical equipment imagery. If measurement, counting or automated analysis will be performed on these files, lossy compression is unacceptable. The artefacts JPG produces change pixel values and can affect analysis results.

Because PNG preserves pixel values one-to-one, that risk never arises.

Genuine photographs → JPG, depending

Photographs transferred from an old digital camera and saved as BMP, product shots, field records. This content is what JPG was designed for.

The purpose is decisive here: if the photographs will be shared, put on the web or emailed, converting to JPG gives the smallest file. But if the aim is archiving, staying with PNG is more correct, because the move to JPG is irreversible and not making irreversible decisions is a general principle in an archive.

Warning: leave some files completely alone

There is one category in old archives where conversion does damage, and skipping this point is expensive.

Files that are input to a system still in operation. An old game engine, a CAD import tool, a production line application or an industrial panel — most of these expect BMP directly and do not recognise PNG. If you convert the files in the folder and delete the originals, the system may stop working.

The method to apply here is simple: keep the converted copies in a separate folder and do not touch the folder the running system reads. You still get the archival gain without taking the risk.

A practical workflow

When working with a large archive, this order helps:

Test with samples. Pick a few files of each content type, convert them, and open and check the results. Noticing a problem after processing the whole folder is far more costly.
Verify transparency claims. BMP's alpha support is inconsistent; files that should be transparent may in fact be opaque. Check after conversion.
Preserve filenames. In old projects assets may be referenced by name; changing only the extension keeps some workflows standing.
Wait before deleting. Instead of deleting the originals immediately, keep them somewhere separate for a while. There is no data loss in PNG conversion, but noticing system dependencies can take time.

In summary

For old BMP archives the default target should be PNG: it is lossless, opens everywhere, delivers serious disk savings and carries no risk of a wrong decision. Choose JPG only for genuinely photographic content and only when the sharing purpose is clear. And most importantly — do not touch BMP files that a running system reads; there, an old format is not a problem but a requirement.