Bitmap images

[Andrew Burton]

Jules Richardson <julesrichardsonuk at yahoo.co.uk> wrote:
> Andrew Burton wrote:
> > Hi, i was reading up on bitmap (mainly .bmp, with 
> > some .wbmp) images 
> > last night and was wondering why  everything is 
> > stored backwards
> > (e.g. BGR instead of RGB and the bottom of the 
> > image first, instead
 > > of the top)?
> 
> I believe the backwards RGB quads* are just a 
> hang-up from the fact that 
> almost every platform which supported .bmp files 
> used an Intel x86 (or 
> compatible) CPU - and Intel's x86 processors store 
> multi-byte values lowest-first.

Yeah, I discovered that out the hard way. Do all Intel CPU's do that or just x86's (and compatibles)?

>
>
> *Going from hazy memory, I seem to recall that 
> colour map entries in .bmp 
> files are four bytes: BGRx, with x being always set 
> to zero. I can't remember 
> if 24-bit direct-colour images also use four bytes per 
> pixel or only three.

Yeah, that's exactly how it works. I assume the reserved bytes (always set to 0!) were to do with aligning values on a 4 byte boundary for the Intel X86?
Not got onto 24-bit images yet.


> 
> No idea why the origin of the image was bottom-left 
> rather than top-left, but 
> there wasn't ever really a standard for this kind of 
> thing (if MS Windows 
> itself sets the origin at bottom-left then it certainly 
> makes sense; .bmp was 
> really only ever popular for MS-Windows, after all)
> 
> > Also would i need to pay a license if i wrote a 
> > program to create .bmp 
> > files?
>
> As far as I know, no.

Ok, thanks. Will check online just to be safe :)


> 
> > My main aim is to write a .bmp to (amiga) .iff 
> > format
>
> Heh, the last time I wrote any .bmp handling code it 
> was to do that the other 
> way around, as I had a bunch of IFF files that I 
> wanted to read on a Windows 
> 3.1 box.
> 
> > , but would love to add
> > full .bmp support to an art program i wrote for the 
> > amiga and then stick it 
 > > online (on Aminet.com ) for other people to use if 
> > they wish.
> 
> Obvious question: why .bmp? As above, it was only 
> ever popular with MS 
> Windows; in the rest of the world TIFF, PCX, or 
> Targa support tended to be a 
> lot more prominent. PCX and Targa seem to have 
> fallen by the wayside these 
> days, but TIFF is still alive and well, and of course 
> PNG has come on the scene.

I have some TIFF and PCX images on old PC disks (from early 90's). Microsoft Paint doesn't support them  (I don't require a proper art program on the PC for what I do) and I doubt the vast majority of PC users have even heard of them.

I got WinCapture, made around 1993, off of one of the old disks and it still works (just about) on Windows 2K. I can use it to capture any image onscreen (except movies read from CD/DVD - I guess because the software is so old?) and turn it into a bitmap image :)



> If I were writing something to export data to an 
> image format these days, I'd 
  > pick TIFF or PNG over MS-bitmap; certainly writing > a TIFF encoder isn't too 
> complex (writing a comprehensive decoder can get a > little hairy due to all the 
> vendor extensions, but writing something to handle 
> the typical flavours isn't 
> hard), and from what I hear PNG isn't too difficult to > handle either.
> 
> cheers
> 
> Jules

Well, like I said the main target is Amiga .iff format, but it would be nice to include other formats for those using Amiga emulators. That way they can transfer images to a PC friendly format for whatever purpose they require them for (website, advert, project, etc.).

It would make advertising my games on my website easier if I can get direct images, instead of using a webcam or digital camera to take pictures of the screen (which turn out rubbish - see http://www.geocities.com/aliensrcooluk/mysite/glists/my_amigagames.html )!
I haven't actually got pictures of GamesVol3 up yet, though it only contains my .ABI encoder and decoder programs. Yes, I created my own image format!
For "simple" images it does turn out smaller than the Amiga .iff format, despite me not using compression in version 1!  I do include example images on GV3.

None of my stuff is actually available online yet, I just sent disk-based copies to 2 fellow AMOS coders - one in Germany and one in the US.



Err... I'm babbling now. Better finish up and read the rest of my emails :)


Regards,
Andrew B
aliensrcooluk at yahoo.co.uk