>  Now, if you do make a gradient from black to white with POV-Ray 3.7,
> the transition doesn't look linear for some reason,

The key point here is "look" linear.  If you did the gradient with 3.7 and 
measured your monitor with a luminance meter you'd find it was a linear 
gradient.  Your eye/brain however doesn't see that as a "linear" gradient. 
(There are various transformations to convert absolute luminance into a 
"perceived" luminance, and they're not linear).

BTW all this (about how your eye/brain works) is completely unrelated to how 
POV should work, POV should attempt to make your monitor display what the 
scene would look like if it existed IRL (just like how a camera works).  In 
this respect if IRL there existed a truly linear gradient from 0% to 100% 
then POV should attempt to make it look the same.  Which it does in 3.7.

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On 01.12.2010 14:31, Kenneth wrote:
> What all of this says to me (and I'm not saying it's wrong) is that, from now
> on, it's "POV-Ray against the world!" The 'world' meaning, all the *other* apps
> (like Photoshop) that we're so used to working with, with their apparently
> flawed way of handling gamma.
>
There is and never was something like POV-Ray against the world. 
Photoshop is a great tool (I'm, using it since the time it was not even 
called Photoshop but Photostyler and was developed by Aldus and not 
owned by Adobe - and a few weeks ago did update to CS5) but it is also 
still flawed in multiple ways and has (as every complex piece of 
software) numerous bugs.

but as Stephen Klebs wrote:
 >like it or not, Momma Photoshop holds the ruler.
...and...
 >A language needs dictionaries like Photoshop to tell us what thing's
 >mean.

well, like it or not, but the only one who will be happy about such 
statements is the marketing department of Adobe - I for one do report 
the usual found bugs back to Adobe and do never trust blindly any piece 
of software. And just as a side-note: the long history of Adobe 
Photoshop is full of changes that also caused particular image file 
formats written by some older version to be rendered completely 
different with the new one.

I'm also using frequently Blender as a modeller and always POV-Ray as 
final render engine for it.

In fact and for short: since the applied gamma handling changes in 3.7 
making POV-Ray work together with applications like Photoshop and 
Blender has become much easier, less painful and without time consuming 
workarounds.

And to put it a bit rude: the only thing that *is* apparently flawed is 
the knowledge of most users about the tools they use - and well, I'm not 
talkin' especially about POV-Ray here ;)

-Ive

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On 28.11.2010 15:46, Stephen Klebs wrote:
> More on the bigger issue:
> I hope I'm not over-reacting here but here goes:
>
> Like most who have used POV for many years, we rely on past examples rather than
> having to reinvent the wheel each time from scratch. This is particularly true
> since POV has evolved into a much more complex SDL - radiosity and photons and
> media and other envelope-pushing features - that, while they expand the horizon
> of possibilities, have also made it much more difficult to efficiently use.
> There seems to be an almost infinite fiddling with parameters and tweaks and
> coefficients to the point that it is all the more necessary, when trying to just
> get something done, to merely borrow on some successful solution others have
> found that just works. It is little wonder that beginners and accomplished
> graphic artists like Gilles Tran have lost interest in POV as a workable,
> practical tool. The addition of macros has helped some but it's gotten so
> cumbersome even long-time users aren't sure what to do to get what they expect.
> Does anyone else still miss "halo, for example, or MegaPov's "glow". Not
> "technically realistic" perhaps but they got the job done.
>
> But as it is now with 3.7, that's all out the window. I tried for example to
> test Steve Gowers' famous "Bucket of Shells", which was originally created in
> 3.0 but still renders the same in 3.6. No matter what I tried, setting #version
> 3.0, #version 3.6, #version 3.7 with any and every possible Display_Gamma or
> File_Gamma or assumed_gamma or gamma whatever, the results in 3.7 came out
> dramatically different. There is in effect no practical backward compatibility
> with the whole tradition of POV. And as for trying to tweak the lighting and
> ambient and diffuse ad infinitum of every light source and color and finish
> etc., etc., one might as well start from scratch. So while a good case has be
> made that POV in the past was technically "wrong", is this more important than
> how it is actually used. Whatever the technical issues, POV worked fine. It
> played well with others. Images came out as expected on the web, in Photoshop,
> on Macs and PCs and Linux. To just say that we were just doing it "wrong" all
> those years for using assumed_gamma for artistic effect misses the point. Who
> cares how we got there as long as we made it and it didn't take a week of
> futzing around. I sometimes think, with all due respect for the enormous and
> wonderful work the developers have freely put into it, that POV has lost sight
> of the end-user who's out there not just to play with the dials and controls but
> just to get something off the ground.
>
>

Just to make sure the OP does not speak for all (or even the majority, I 
hope) of POV-Ray 3.7 users: *I* am very grateful for all the hard work 
that has been put into the change of the gamma handling.

I am a long time POV-Ray user (since 2.0 IIRC) and prior 3.7 I was 
always forced to use workarounds to make sure POV-Ray is indeed working 
internally in linear color space. And I will not repeat once more why 
this "linear color space" thing is important for a ray-tracer as this 
has been said so often that I'm seriously bored by its repetition.

And I'm also glad that POV-Ray 3.7 now works without the need of time 
consuming workarounds together with applications like Poser, Blender and 
Photoshop.

just my 5ct
-Ive

P.S.
and I do not like that the OP does imply that Gilles Tran's (who was 
always one of the first who did use every new feature POV-Ray had to 
offer and did quickly adapt to all changes) motivation to switch over to 
some commercial render engine was in any way related to the OP's 
complains. As far as I remember Gilles reasons where more along the 
lines that he thought POV-Ray is taking to long to adapt to new render 
technologies like e.g. physical based rendering and such...

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"scott" <sco### [at] scottcom> wrote:
> >  Now, if you do make a gradient from black to white with POV-Ray 3.7,
> > the transition doesn't look linear for some reason,
>
> The key point here is "look" linear.  If you did the gradient with 3.7 and
> measured your monitor with a luminance meter you'd find it was a linear
> gradient.  Your eye/brain however doesn't see that as a "linear" gradient.
> (There are various transformations to convert absolute luminance into a
> "perceived" luminance, and they're not linear).
>
> BTW all this (about how your eye/brain works) is completely unrelated to how
> POV should work, POV should attempt to make your monitor display what the
> scene would look like if it existed IRL (just like how a camera works).  In
> this respect if IRL there existed a truly linear gradient from 0% to 100%
> then POV should attempt to make it look the same.  Which it does in 3.7.

Herein lies the fundamental argument between the two opposing camps: Should
POV-Ray imagery be presented to us (on-screen and in images) as
scientifically/technically accurate--"what the scene would look like if it
existed IRL"--or should it look "pleasing to the eye" (vis a vis Photoshop etc.)
and therefore, by nature, non-accurate? (That's just a philosophical question,
not meant to be answered.) Both camps have an equally valid point of view,
within their respective realms. (Of course, that might sound like I'm treating
the matter as 'just a matter of opinion', when it really isn't, for the many
technical reasons given.) Happily, the gamma 'switch' being discussed should
alleviate these concerns, from a practical standpoint--those of us desiring a
'visually pleasing' (though admittedly non-accurate) way to work can still have
it.

BTW, your post(s) have given me greater clarity as to the underlying reasons for
the 3.7 gamma change, what to expect and why. Many thanks.

Ken

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Am 01.12.2010 14:00, schrieb Stephen Klebs:
> clipka<ano### [at] anonymousorg>  wrote:
>
>> Photoshop is a liar when it comes to color maths.
>>
> You've obviously never worked as a graphics artist. Eventually, everything goes
> through Photoshop at one point or another. If Photoshop is a "liar", then the
> lie is the truth. Us kids have to play with a lot of multi-colored graphics
> tools - raster and vector and tracers and converters and raytracers and scanline
> and cad, etc. - but we can't play nice together without some supervision and,
> like it or not, Momma Photoshop holds the ruler. Otherwise, we can just play

As a graphics artist, you're probably familiar with color profiles, and 
will be well aware of the fact that different devices use different 
color spaces - not only with different primaries and whitepoints, but 
also with different transfer functions. They're not doing it for fun, 
but because that's simply their "native" way of representing colors.

Similarly, there is a "native" way of representing colors in a 
raytracing engine - and that's linear /physical/ light intensity.

You're probably also aware that Momma Photoshop doesn't have any 
"native" way of representing colours: You can work with it in sRGB color 
space, Adobe color space, wide gamut color space, and a ton of others - 
each with its own definition of what pixel value 128 or "50% grey" mean.

So no - "Momma Photoshop" cannot be the ruler for POV-Ray, because it 
doesn't really have fixed rules. It just manages the laws according to 
which you decided to live. The ruler it holds is just the one you 
happened to put in its hand. (I guess there's a policy at the place you 
work, as to what color profile to use by default.)

So if it helps you, think of POV-Ray 3.7 as using its own color profile 
(though it does not /yet/ make such a sophisticated approach at colors; 
for now all it handles is gamma), and you'll realize that you need to 
feed it data adjusted to that color profile to get it to do what you 
want to.

Fortunately for you, during its long beta-phase POV-Ray 3.7 has also 
developed a set of tools to help you work with data that doesn't fit its 
"native" color profile, to save you a lot of work converting your "raw 
material" to POV-Ray's color space (and converting its output back),

For input images, there are automatic conversions in place for the most 
typical cases in the amateur world (POV-Ray 3.7 will presume sRGB for 
most file formats, and honor PNG sRGB or gAMA chunks), and if you need 
something more uncommon you can always use the "gamma" keyword.

For color literals (which are input, too), POV-Ray 3.7 has no sane 
stable and consistent choice than to require them to be specified in its 
"native" format, but will offer you the "gamma" keyword there, too, to 
make life a little easier for you.

For output images, POV-Ray 3.7 will again do what amateurs are most 
likely to expect: Output will be close to sRGB (currently still 
defaulting to a power-law gamma of 2.2 though if I'm not mistaken); 
however, the "File_Gamma" INI file option will again allow you to 
generate data that better suit your needs.

Likewise, POV-Ray 3.7 allows you to tune the preview window output to 
your display's working color profile via the "Display_Gamma" keyword.


(You may note that I'm talking about color profiles here when in reality 
it's just a small aspect of it - gamma (or, more generally, the transfer 
function). That's because in the long run I hope to be able to make 
POV-Ray fully color-space aware, to even better interface with the 
outside world.)


As for your overused gradient example, I challenge you to make the test: 
Open the image I just posted in "p.b.images" ("Gamma challenge image"), 
and tell Photoshop /not/ to convert it to whatever your working colour 
profile happens to be (you may need to change your colour settings so 
that Photoshop will ask), and then try to draw a smooth gradient.

So much for Momma's Holy Ruler. And it's not necessarily tied to an 
image: You can even use similar settings as your default working colour 
profile.

Pardon my french, but Momma Photoshop is a bitch.

Post a reply to this message

> Christian Froeschlin<chr### [at] chrfrde>  wrote:
>> Independent of this issue: Would it be useful to have a
>> setting of "color_gamma" that tells POV-Ray how to interpret
>> literal color values specified in SDL? The default value of 1.0
>> would yield the current behavior while e.g. 2.2 would internally
>> convert a value as rgb 186/255 to rgb 0.5 without the need for
>> plastering your code with gamma macros.
>
> Or a global_setting to toggle like default settings that just stipulate: for
> every pigment past this point assume every color raised to the power 2.2 or 1.8
> or whatever but then we're back to assumed_gamma again. The trouble is too that
> ambience and light intensities and a whole host of other variables
> are also playing their part. At this point, I would just like to see 3.6 ported
> with multi-processor support.
>
>

Yes, and then you get scenes with some very weird assumed_gamma values, 
like: -2.7, 7.8, 0.1, 19,...
Pure madness.


Alain

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El Wed, 01 Dec 2010 17:06:17 +0100, Ive escribió:

> Just to make sure the OP does not speak for all (or even the majority, I
> hope) of POV-Ray 3.7 users: *I* am very grateful for all the hard work
> that has been put into the change of the gamma handling.

  Me too!

> and I do not like that the OP does imply that Gilles Tran's (who was
> always one of the first who did use every new feature POV-Ray had to
> offer and did quickly adapt to all changes) motivation to switch over to
> some commercial render engine was in any way related to the OP's
> complains. 

  Yes, IIRC, Giles reasons were just the opposite!

-- 
Jaime Vives Piqueres
		
La Persistencia de la Ignorancia
http://www.ignorancia.org

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I did not intend to raise such a hornet's nest here (maybe I did). But the
debate is fascinated and it was great to see such life in the forum. It's been
*enlighening*, as it were. Those in the light lab and those in the art studio.
The difference to me is that one is trying to reproduce the behavior of light as
faithfully as possible, the other is trying to re-create an expressive picture
of things so that this physical input can be transformed as experienced by the
human eye.

(I still say, they are not the same process but it's too hard to get into. Can't
help but try a bit: I would say that what constitutes a convincing picture is
not just what a perfect camera would record. Even photography, as Clipka points
out, is not accurate. But not because it's flawed but because photographers know
that to bump the red or distort the perspective they can acheive more dramatic
and eye-catching results. Pure simulation looks boring. TV is way
over-satruated. Why? Because that's how people want to see it. That's what
"looks good.")

All these complaints, of course, are completely unfair to those in the light lab
trying to compute the refraction of photons off a wine glass or the scattering
of the setting sun through a cloud. We seem to be seeing opposite sides of the
picture. One side assumes that by just reproducing how light is projected from
objects onto the screen that that is enough, since past that point the eye is a
mere recording device. The other that that display is just a pattern of points
of color that has to be perceived, re-seen, if you will, by the human eye to
give it coherence, meaning, and going further. artistic expression. Both have
their place. But one should not impose the limits of its view on other. And by
changing the rules of the game it makes it hard for some of us to know how to
play.

My original concerns were really pretty practical and I confess that even though
POV is, after all, a raytracer, unique in its faithfulness to the physics of
light -- time-consuming as it is, that I usually use it less as a programmable
camera than as a painter's palette, more like the java-based Processing, but in
3D. Because of their strength as languages, the downside is that you're always
working blind. You put words in the little black box, mix up the ingredients,
shake it around, put it the oven and let it bake, often for a very long time.
but never really sure how it will come out. So you have to come up with a lot of
tried and true recipes, techniques and formulas, that you rely on to predict
more or less how it will taste. My main concern was that all these hard won
recipes were now no longer reliable. Like someone put salt in the sugar bowl or
what I thought was vinegar is now sweet as milk.

My other concern has to do with the fact that all this has to be done in the
dark. So you need some kind of crutch to hold onto, a frame of reference other
than the glow from the little POV display, patiently pixel by pixel spiting out
the results. In my case, it's Photoshop, Momma or "bitch", that tells me how it
will look to others, in various situations, on different paper with different
ink on different tables. If I want to print it or web it or animate it into a
cartoon. It also gives me some way of testing it. There's nothing special about
Photoshop here (though as software goes it's pretty dependable) but since it's
what everyone uses, I know that when I try to communicate my cool little
creation to others (a web site or print house or wherever) that they will enjoy
it pretty much as I obviously hope. If I tell POV "rgb 0.5" to tell Photoshop
"rgb 128" then what do I say? I can change the definitions, of course, and say
well now 0.5 is scaled to mean 186 but the power of 2.2 is a little hard off the
top of my head.

Now from my initial tests both of these security blankets threatened to be
thrown in the washer. My recipes didn't seem to work any more and what I was
getting in Photoshop wasn't what I expected to find. Not just how it looked but
how the numbers added up. So, yes, I could rework everything and start from
scratch but let's be practical here, to try to put back together the pieces of a
broken Lego is infinitely harder than making it in the first place. Plus I can't
understand the old instruction book anymore. Then what to do? Move to a new
kitchen like Cinema 4D or Maya, where the equipment is more convenient, you can
taste test in real time, and the microwaves are faster. But these metaphors are
getting way overdone and that's about all I can say.

Post a reply to this message

"scott" <sco### [at] scottcom> wrote:
> > Bluntly put. You're making this much too complicated. It's certainly less
> > complicated than dealing with color management for print. You make a
> > picture
> > that looks good on your computer. It doesn't matter how you do it.
>
> In something like PhotoShop, sure, but POV is almost a light simulation
> tool, it needs to follow the correct laws of physics in the first place.
> Sure you can botch it and create something that looks realistic, but it
> won't be exactly physically correct, and usually would require a great deal
> more skill and effort from the artist.  POV works on the fact that if it
> deems something should be 50% brightness, it will make it look 50%
> brightness to you (which is not the same as 50% pixel value).  If it didn't
> work this way it becomes impossible to get scenes with physically correct
> lighting, and then you need to start the whole skillful and time-consuming
> "bodge" process of trying to make it "look right".

This makes the point very clearly. But in the particular example of the
gradients that for me set this off was that I was trying to deal with a
completely graphics issue: rgb 0.5 ambient 1. There is no light involved here.
Ambient is not a real property, it is a completely artificial adjustment control
that does not exist in the real world. Some of us are not always dealing
necessarily with how much light is reflected off a piece of white paper in the
real world. We just want to make a picture by telling POV give me rgb 128.

Post a reply to this message

I might add there are several terms and keywords, besides ambient, in POV,
parameters that can not be translated directly into the physics of light. They
are there basically as adjustments and control knobs not any different than
adjusting the brightness or contrast on your TV. Specular, diffuse, metallic,
noise -- while these have optical counterparts they are terms and concepts
developed by computer graphics, even in scanline, where the goal is just to get
as quickly as possible, by whatever means, a result that looks right. Perlin did
not come up with his famous noise factor because of physics but because by
chance it just happened to be a good way of visualizing certain things. It
wasn't like he
said I want to find an equation for how clouds look, but more like "hey, this
formula makes pictures that look just like a cloud." POV is a raytracer but it
is also a computer graphics tool and they do not use completely the same
techniques.

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