2000.10.04 16:04 "RE: BMP questions", by Chris Losinger
I suppose that delta escape can be usefull in images that are not meant to be universally readable but are only intended for some particular app to use. In that case the app would surely know what to do with them, and they could probably cause a serious compression sometimes. So I guess that 'private' use was the original intention of the delta escape.
i have always assumed that deltas are intended to be used on AVI sequences. in AVIs, each frame is a DIB (a BMP without a BITMAPFILEHEADER). with delta escapes, you can update small areas of successive frames, instead of having to store and decode the entire frame each time. this makes a lot of sense in animations.
My advice is, even if you should come accross some document that pretents to have an answer, not to support the delta escape in BMP writers because the only purpose of that would be discovering that there are absolutely no readers that support it.
actually, there are lots of readers that will read RLE's (ACDSee, for one, and anything written with my company's tools, for two and higher).
and now for the fun part: according to the MS docs, DIBs (and hence BMPs) can now contain actual PNG and JPG files in them. kill me now.