2006.09.18 09:40 "Re: [Tiff] isthere alphacomponent presentin GrayscaleorPalettecolorimage", by Joris Van Damme

Graeme,

Though I'm not sure if more people then us two are still reading, except perhaps one or two who find some entertainement value here, I find this an interesting conversation.

As far as I understand what you propose above, you seem not disagree with my statement, in fact you're looking for a suitable distance measure in the L*a*b* alpha space that is *not* normal eucledian distance.

Probably not, but does it matter? If something like variance cut were being used to quantize the result, computing Euclidean distance then doesn't come into it.

Note that in my original statements, I talked about dithering as an example. You next took quantizing as the example operation. While any notion of distance may be less important in quantizing, it is certainly relevant in dithering.

I'm not a real world guy. Except after the theory's in place, and I do seem to cover some ground that way. That means, when I'm about to do arbitrary things, I take that as a strong hint I made a wrong turn somewhere. If I need to magically jump from A to B, I take that to mean I shouldn't have followed the road signs loading to A in the first place.

Ah well, that's the difference between us then. I'm an Engineer, so I'm not going to get stuck trying to figure the theory out to the n'th degree, when trying something out will take me down the path of discovery faster. Even if trying something out doesn't give a workable result, it might provide enough extra information to determine what theory applies, and how.

I do have stuff like this (quantizing and dithering of L*a*b* alpha) implemented in my ancient Delphi code, tweaked by experiment until I got pleasing results. Doesn't really matter, except that it shows I do agree with you sometimes one just has to go ahead even if one suspects there's something fishy about the whole situation. Is one of the good reasons why I never used words such as 'The Wrong Thing' but instead refered to it smelly and fishy, and merely came up with the recommendation to avoid RGBA palettes it if possible.

The key word being 'RGBA palettes', because that shows where clearly spinning off-topic. In my original recommendation, I did mention RGBA palettes may be possible in TIFF depending on your take on the Indexed tag. Nobody ever implemented support for the Indexed tag as far as I know, and using it to store RGBA palettes may be ambigious. So it's not exactly even an issue in TIFF really.

You can't build a model on the basis of a particular chosen scale that hides the fact you're throwing in arbitrary chosen constants and expect to make sense. But you may indeed expect that perhaps you're getting more or less pleasing results. If that's the goal, fine. I'm not saying it shouldn't be the goal. But I do think the words 'fishy' and 'a bit weird' apply, and I suspect there's turns and quircks, maybe earlier on that road, that aren't exactly theoretically solid, and/or at least room for more investigation or thought.

What scale should one use for "shininess"? What about "sharpness"? How about "transparency"? What theory would guide you?

Your point being that all of us end up doing lots of stuff without solid theoretical basis? In that case, I'll have to agree with you again.

Sorry, Graeme, perhaps I'm stupid, but I can't find much disagreement, yet there seems to be a lot of discussion. If the core of this is due to my bad use of English, I appologise.

No, I think we're communicating pretty well, and I'd certainly never pick you as a non-native speaker of English - but then I speak "Australian" :-)

Oh please, of course you've picked me up as a non-native speaker of English, I can't even spell let alone build a desent sentence.

Best regards,

Joris Van Damme
info@awaresystems.be
http://www.awaresystems.be/
Download your free TIFF tag viewer for windows here:
http://www.awaresystems.be/imaging/tiff/astifftagviewer.html