Comments in WMF files

Windows Metafile (WMF) is a vector graphics format native to Microsoft Windows 3.x. It was succeeded by Enhanced Metafile (EMF) in 32-bit versions of Windows, but it seems to have remained in use, alongside EMF, long after Windows 3.x became obsolete. It was often embedded inside other file formats, such as PowerPoint (.ppt) or Write……

The finer points of TIFF “ASCII” fields

This post concerns the TIFF image file format, and some related formats: Exif, DNG, and JPEG XR. A TIFF file contains a set of “fields”, each of which contains some sort of data element. Each field has a “tag”: a code number that tells, logically, what is stored in the field. For example, tag #256……

JPEG thumbnail formats

How many ways are there to put an extra “thumbnail” or “preview” image inside a JPEG (.jpg) image file? This isn’t just trivia. One problem with thumbnails is the possibility that they might be neither updated nor deleted when the main image is edited. If you’re not careful, your edited JPEG file could contain a……

GIF plain text extensions

Plain text extensions is an obsolete feature of the GIF (version 89a) image format. Essentially, it allows an animated GIF to have ASCII text frames, as well as the usual graphical frames. As far as I know, it was pretty much never used at all. The only GIF file with plain text extensions that I’m……

X-Face format

X-Face is an odd little graphics format, designed around 1990 as a standard way to include your picture/icon/avatar in the email messages you send. It’s not exactly a file format; it’s a special string of text that can be included in email headers. A number of email applications supported it, and maybe some still do.……

Survey of MacPaint brush patterns

MacPaint is a paint program for early Macintosh computers. You can see it, and try it out, at the Internet Archive: <https://archive.org/details/mac_Paint_2&gt;. Its native image file format is very limited, and very obsolete. But a large number of MacPaint files were created, back in the day, and some of them can still be found. For……

Corrupting ZIP files

The ZIP (PKZIP) compressed file format is organized in a backwards fashion. To unzip a ZIP file, you start by looking for a special byte sequence near the end of it. This is a marker for a data structure (the end of central directory) that points to other data structures that appear earlier in the……