This topic has caused me to think about something that Iíd considered settled. As often happens, this kind of thinking has made me question what I thought I knew, and raised as many issues as itís settled.
Iíve created a list of file types in order of increasing processing required for rendering, and also in order of decreasing determinism Ė the types later in the list tend to have a wider variety of acceptable renderings. The two qualities are not perfectly correlated, and Iíve had to apply subjective weightings to, if you will, turn a vector ranking into a scalar one. The distinctions are rough, as there are so many file formats that, once processed, result in images.
A. Raster-arranged files in the color space of the intended output device. Examples are gray gamma 2.2 for a particular monitor, sRGB, one of the SWOP CMYK standards. In the case where an offset press is the output device, the data in the file is halftoned. In the case where an inkjet printer is the output device, the data is also halftoned Ė this image form is hardly ever saved on a disk except for spooling.
B. Raster-arranged files with tags enabling appropriate processing for a range of output devices. Examples are PSD, many TIFF variants with ICC profiles attached, and raw files. Raw files sometimes need data thatís not in the tags for acceptable processing.
C. Quasi-raster-arranged files with non-raster data included. Examples are the discrete cosine transform coding of the original JPEG, the wavelet coding of JPEG 2000, and, I believe, all of the MPEG video formats.
D. Vector files with or without raster elements. May contain data types that require artful interpretations to rasterize. Examples are Adobe PostScript, Adobe Acrobat, native Adobe Illustrator files.
E. Formatted text files with embedded graphics elements. Examples are Microsoft Word files, TeX files, RTF files. InDesign files could go here or in the category above.
F. Plain text files, or files that do not uniquely specify the ultimate raster image. Examples are TXT files or early HTML. HTML has been heading in the direction of category D of late.
I think most people would agree that category A files are image files. I think most people would agree that category F files are not.
Where do you all think the line should be drawn? Or is it enough to agree that, in this context, image file is not a binary term?