And lo on Wed, 07 Jul 2004 16:14:53 -0500, Christopher James Huff  
<cja### [at] earthlinknet> did spake, saying:

> In article <opsaret2miefp2ch@news.povray.org>,
>  "Phil Cook" <phi### [at] nospamdeckingdealscouk> wrote:
>
>> Well commenting out assumed_gamma produces a darker image on the 'gate'
>> with no Display_Gamma set, so default gamma correction of 2.2 is in use.
>
> No, gamma correction is off by default. (At least, it's supposed to be.)
> It gets turned on when you include assumed_gamma in the global settings.

Yes sorry quite right.

>> Just to check this I changed the two planes in "Magic Gate2.pov" to the
>> same colour as that in "Magic Gate1.pov" and ran it both ways, without
>> assumed_gamma produces a noticeable difference.
>> I've posted a tiny file in p.b.images to show the differences.
>
> Weird. If you want the rendered image to appear the same as the original
> map, you obviously don't want any gamma correction to be done...the
> corrected version won't be the same. Your image doesn't show the
> original map, so I can't compare...but the fact that it shows up
> differently from the surrounding scene, which should be the same color
> pre-correction, is very odd.

Which is what I thought both images should have either none or the same  
correction applied

> What formats are you using? It may be an artifact of however POV and
> your other image software handles gamma values in PNG images. You should
> get the effect you want if you render the map without an assumed_gamma
> value, and the final image with assumed_gamma 1.

Magic Gate2:PNG read by Magic Gate1 with again PNG output that's runnng  
both files with assumed gamma 1. That's interesting, running MG2 with  
gamma 1 and MG1 *without* matches fine, reversing it is still darker.

So to summarise:

MG1 without gamma, MG2 without gamma: MG2 darker image within MG1
MG1 with gamma, MG2 without gamma: MG2 darker image within MG1
MG1 without gamma, MG2 with gamma: Match colours
MG1 with gamma, MG2 with gamma: Match colours.

Okay might have it switched to using bmp instead of png:

MG1 without gamma, MG2 without gamma: Match colours
MG1 with gamma, MG2 without gamma: Match colours
MG1 without gamma, MG2 with gamma: MG2 lighter image within MG1
MG1 with gamma, MG2 with gamma: MG2 lighter image within MG1.

What fun! Oh well I've got it to match so I'm not too fussed still  
interesting.

>> > Anyway, in addition to setting ambient to 1, you should set diffuse to
>> > 0, so light from scene illumination won't wash out the image.
>>
>> diffuse 0 doesn't seem to make a difference but of course might once I
>> start changing the landscape.
>
> Try shining a bright light on the gate.

Well once I start to work on the landscape I'll see how it goes.

--
Phil Cook

-- 
All thoughts and comments are my own unless otherwise stated and I am  
happy to be proven wrong.

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