Le 17-09-10 à 14:50, Stephen a écrit :
> On 10/09/2017 16:23, clipka wrote:
>> Am 10.09.2017 um 15:55 schrieb Stephen:
>>> A while ago when I was working with df3s. Both Alain and Clipka
>>> mentioned that df3s use grey levels not three channels of colour.
>>> Tga2df3.exe creates RGB df3s (The utility Oosawa 4D Volume Viewer, can
>>> split them using only one of the channels).
>>> How does PovRay's internal workings handle this, mathematically?
>>> If PovRay reads a value of (say) <0.5, 0.7, 0.1> what density value
>>> would it give it?
>>> Similarly for <0, 0.9, 0> or any other combination of colour components?
>>
>> To the best of my knowledge, there is no such thing as a RGB DF3, so
>> you're asking the wrong question.
>>
> 
> Knowing that you are asking the wrong question is always good.
> 
> 
>> The right questions should be, "how does tga2df3.exe handle RGB colours
>> mathematically?" and "how does OOsawa 4D Volume Viewer get colours out
>> of it?"
>>
>> I would presume tga2df3.exe uses the greyscale value (or an average of
>> the channels) from the images; and that OOsawa 4D Volume Viewer
>> essentially just uses a colour_map-ish system to convert density to 
>> colour.
>>
> 
> I'm not convinced. I distinctly remember Oosawa telling me that the 
> opened df3 was not monochromatic and asking me which colour channel to 
> use. I say remember because I had an unfortunate accident with my PC and 
> lost all the data on it and my backups did not work. <insert obscenity 
> here> And when I downloaded the current version. That did not happen. 
> When I looked at a newly created df3 by tga2df3 in a hex editor it was 
> 95% nulls.
> So I will just grumble to myself. :-(
> 
> 

Maybe it assumed that any gray level DF3 would use only a single byte 
per voxel, and wrongly concluded that more byte per voxel meant that it 
was to be interpreted as some kind of RGB DF3.
If that's the case, in a 3 byte per voxel format, the first byte would 
be assumed to represent red, then the next green and finally blue.
A 2 bytes (16 bits) per voxel would be encoded as 5,5,5 or 5,6,5 bit per 
channel, and a 4 bytes (32 bits) as 10,10,10 ; 10,11,10 ; 11,11,10 or 
10,12,10 bit per channel.

The DF3 is intended to be gray scale, but misinterpreted as been colour.


Alain

Post a reply to this message