TIFF and LibTiff Mail List Archive


2000.10.04 08:38 "BMP questions", by Martin Bailey
2000.10.04 14:02 "RE: BMP questions", by Luc Van Asch
2000.10.04 14:22 "RE: BMP questions", by Martin Bailey
2000.10.04 15:02 "Re: BMP questions", by Peter Nielsen
2000.10.04 15:13 "Re: BMP questions", by Joris Van Damme
2000.10.04 16:04 "RE: BMP questions", by Chris Losinger

2000.10.04 15:13 "Re: BMP questions", by Joris Van Damme

Thanks - I'd been through those already, but there were a few questions that they (and the official documentation) didn't provide answers for, like the fill colour to use when you get a delta escape in an RLE compressed image.

Well, that's easy enough to answer: nobody really knows.

Few BMP writer use RLE because the specs aren't really all that clear. Even fewer use RLE4 because the specs are really hard to understand on that. And I've never ever seen a delta escape because, indeed, the specs do not say how to use them, or, in particular, what fill colour to use.

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.

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.