Am 01.12.2010 01:48, schrieb Stephen Klebs:

> With regard the new gamma model that's being applied to POV, two points: POV is
> first a description language not like Photoshop were you just slide sliders back
> and forth until things look right. There is nothing wrong and even wonderful
> about this approach as long as you have immediate visual feedback. In POV you do
> not. It's like taking photographs in the pre-digital age. You use an educated

I fully agree here: POV-Ray should not be a tool where you need to tweak 
and try until everything looks right.

But that's exactly the point: As long as you don't do proper gamma 
handling, you /will/ need to tweak and try - not for the individual 
colours, but for the scene lighting - to get it look /somewhat/ 
convincing (and it's guaranteed that you /cannot/ get it completely 
right except for trivial scenes).

With proper gamma handling, specifying colors gets a little bit more 
complicated if you're used to color values from image processing 
software, but a simple rule of thumb to always put "gamma 2.2" or "gamma 
srgb" after any color literal should get you going. And you'll have a 
much easier time lighting your scene in a convincing way.

> curve but is a curve. So to get to the point of the gradient example. It tells
> POV that we want a linear succession values over a certain distance what it does
> is give an exponential curve. That's fine but not what I intended and, if you
> can't depend on 1 plus 1 plus 1 etc coming out a 3 or 4 or what ever, how do you
> use a language that's going to be retranslated to mean something totally
> different than what you expected it to say.

No, the point here is that what you expected wasn't what you told 
POV-Ray to do, because despite all your knowledge about human visual 
perception you forgot that a linear succession of brightness values - 
which is what you told POV-Ray to do, and what POV-Ray did - isn't 
/percieved/ as linear.

So essentially you told POV-Ray to add 1^g plus 1^g plus 1^g etc, and 
expected it to come out as 3^g or 4^g or whatever.

> In 3.6 the evenly ramped gradient looked right. The values reported in Photoshop
> or whatever said yes indeed 1 plus 1 is two. I've used POV in every possible

Photoshop is a liar when it comes to color maths.

Ever tried to blur a pattern of alternating black and white horizontal 
stripes, and wondered why the result would be darker than expected?

That's because Photosop thinks 1^g + 1^g = 2^g. Unfortunately that's 
only true for g=1, while normally it will be about 2.2.

> way, on Macs and PCs, to make images that looked fine in IE and FireFox or
> Chrome or in print, and have in fact never encountered problems as serious as
> this major revision seems to solve. I would like to see a concrete scene we
> could render in both versions where it is demonstrated the need for the change.

See p.b.images.

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