Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!swrinde!elroy.jpl.nasa.gov!jarthur!uunet!mcsun!unido!uniol!Marco.Eichelberg From: Marco.Eichelberg@arbi.informatik.uni-oldenburg.de (Marco Eichelberg) Newsgroups: comp.graphics Subject: Re: IFF? (more like semi-IFF) Message-ID: <4923@uniol.UUCP> Date: 1 Mar 91 15:46:27 GMT References: Distribution: comp.sys.amiga.programmer Organization: University of Oldenburg, Germany Lines: 53 nv89-nun@alv.nada.kth.se (Nicklas Ungman) writes: >I've got a copy of Intro to Amiga IFF ILBM Files and Amiga Viewmodes >and it says that "if the picture is 6 planes deep and has no CAMG chunk, >it is probably HAM". Is this really correct? If it is, it means I have >to put a 'CAMG' chunk if I want to save a non-ham 6-bit picture. Does it >apply to 7 and 8-bit pictures too? >The Intro also says that "Hopfully,... the package that saved it properly >saved a CAMG chunk". How is "probably" and "hopefully" defined in an IFF >algorithm? Does they implement a random function to determine if a CAMG >chunk will be included :?) >I also would like to know if Amiga programs (like DeluxePaint) can handle >6, 7, 8 and 24-bit IFF pictures. 1. As you might know, the Amiga is not able to display more than 32 colors at a time in FULL MULTICOLOR. That means, if you want to display a 6 bitplane picture, you can do this as HAM (hold and modify) or as EXTRA-HALFBRITE. Halfbrite means that the 2nd half of the palette is identical to the 1st half, but with less (half) brightness. The HAM-Mode can display all 4096 colors simultaneously, but from one pixel to the next you can only choose one of 16 colors or change one of the three color-values red, green and blue. The problem is that IFF has no mean to save information about the way the picture has to be displayed. For IFF every picture is multi-color. So a program has to determine on its own, if a 6-bitplane picture is HAM or Halfbrite - or even a true 64 color picture from another computer. This is *usually* done by assuming that a 6-bitplane-picture with CAMG chunk is Halfbrite and everything else with 6 bitplanes is HAM. The problem is: this way of determining the display mode is *not* part of the IFF standard, but a kind of work-around. This means, that there is (for a program) no way to be shure that the assumption about the mode is true. 2. One idea of IFF is to make Load and Save shure. So an IFF loader has to provide means to load a picture even if a chunk that is not of great importance is missing. An IFF save routine *should* write all needed information, of course. 3. As far as I know, there is no Amiga program that can handle more than 6 bitplanes. There are, of course, programs for HAM and halfbrite. Some video-digitizers use 24-bitplane-pictures and thus have software to handle 24-bit IFF pictures. The problem is: There is no standard for 24-bitplane-pics. This means that two programs writing 24-plane-pics *may* save the bitplanes in opposite order. Best Regards, Marco Eichelberg