Pretty please. We've had that discussion over and over again. I use Posers Gamma Correction and it gives much better results than using GC afterwards. 

I've removed some postings here, and if this isn't going well soon, I'll lock this thread.

After several attempts to position and adjust intensity, I get a pretty nice portrait. Great. Yes it can be done without using GC. But it took many steps, and lots of test renders.

Much as I adore your explanations of the mathematics of the render engine - and studying this has shed a fair bit of light on my earlier questions and misunderstandings - I'm pretty sure that the convinced of error cannot be unconvinced even with irrefutable logic and sound explanations. I have read Kawecki's explanations, but they don't reflect an understanding on how the Poser Firefly render engine works. He keeps looking at his monitor as opposed to looking at colour-space.

I'm afraid it's a waste of time, except for the fact that I learn something every time you explain it, Bagginsbill. And I'm of fairly mean intelligence. But I am able to follow. Thank you for taking the time, once again!

The phrase: "none are so blind as those that do not wish to see" appears to apply here.

Now here's where the wheels fall off for many people trying GC for the first time.

They start with a scene in which they manually compensated for gamma by adding lights and increasing light levels.

Then they flip on GC and don't do anything else. What happens?

This.

This is not because GC is on. It is because GC is on with overlighting, and all the numbers now mean something different, and the results are crazy bright. There is no dark side anymore.

Even this is not nearly so bright and zapped as many users experience. I'm starting with quality shaders that do not have Diffuse_Value = 1. I'm starting with specular that was set up correctly for the GC (accurate response) situation.

If I had started with no bias towards any of the best practices in CG, and was living in the Poserverse of 2003, turning on GC would seem like a horrible thing to do.

It's not. Rendering like it's 2003 is horrible. It's really limiting. You can't change things and just render. You have to tweak all over the place, and test and test and test.

I use one inifinite or spot. I turn on IDL. All the fill lighting that I worked so hard to create earlier, to give the appearance of being indoors, is now totally automatic.

How do I light my scenes? I use one light. Or no light. Lighting is so easy it's stupid. You want to know why I use IDL + GC + Scatter? Because everything works right with zero effort. That's why.

It's not a unique result. It's a uniquely easy means to the same end.

You can prepare your image for 10 hours and still not produce the results I get instantly.

This has GC off and tonemapping at 1.6. It's not the same, but it's better than nothing.

I once posted a graph showing how a combination of tone mapping and shader GC at gamme = 1.3 could get you closer to accurate luminance results. I don't remember where that is anymore.

Folks, please don't fart about with your (LCD) monitor's gamma setting. It was calibrated at the factory to be correct, and will take many years to significantly deviate from that ideal, if at all.

Your monitor's gamma settings may be labelled as 'Gamma 1', 'Gamma 2' etc. but these are just labels and have nothing to do with the actual gamma values they invoke. Somewhere in your monitor's user guide it will tell you what values the labels signify. You want the one that selects gamma = 2.2.

Monitors that can work in a truly linear fashion - i.e. where gamma = 1 - are pretty rare, and since I'm lucky enough to have one, I can tell you that the linear mode is useless for normal work. It's only used for hardware calibration. 

When I see another gamma question posted here my heart always sinks because all the usual guff will come to the surface. Over-complicated explanations and formulae, which may or may not contain useful facts, will be thrown around and pretty soon the answer to the original question is lost in a mire of gibberish.

Unfortunately, artbee, "why do I need gamma?" is a question that invites complicated answers. 

Better to ask, "Why would I want to use Gamma Correction?". The simple answer is that, as BB says, it takes the hard slog out of so many things. It makes things you do with lighting and shaders produce predictable, consistent, accurate results. You have to understand what it does and learn a few things, make some changes to your workflow, and that's about it.

Look at BB's images over the last few posts and you should be able to see why it's a good idea. That should motivate you to figure it out and use it properly.

Quote - Look at BB's images over the last few posts and you should be able to see why it's a good idea. That should motivate you to figure it out and use it properly.

^^^^^^

This.  

thanks for the support. I got the answer doing some measurements, with just Gamma=1 (red) and gamma=2.2 (teal), and also exponential tonemapping added to them, with expo=1.6 (default) or 3.2 (double exposure). Measurements were made in all six cases, in three rounds with varying lighting conditions, and 9 points per round.

My conclusions:

1. when you want to post process the image, especially when exporting to HDR or PSD or working with render passes in any other way, tonemapping as well as gamma should best be off. This matches Robynsveil's linear way of work. you might take the teal curve (is about  [0,0] [20,50] [50,75] [80,90] [100,100] ) for curve adjustment in Photoshop.

2. when you want the image just to look good without that much postwork, gamma is fine and 2.2 does the job by pumping more dynamics into the dark areas as shown in the mirror-example by BB in this thread (teal curve). However, no gamma but a serious exponential tonemapping does a similar job (green curve).

3. applying exponential tonemapping with 1.6 leaves the overall luminance of the image at the same level, but adds some detail to the darks while taking out some from the hilights. This is great for fashion shoots where usually the model is mildly overexposed to shift the attention to the clothes. It works just on top of the gamma effect (orange and blue curves).

4. tonemapping and gamma add on to each other, both pump up the darks at the cost of losing detail in the hilights. Gamma is stronger on increasing the nuances in the darks and handling underexposure, while tonemapping is stronger in reducing detail in the hilights and handling overexposure.

So, do I need gamma, and are there alternatives? Well, the final result will profit from a "serious and non linear brightness correction", that's for sure. This can be done in post, in Poser GC and in Poser tonemapping, in any combination. Doing none of them is a shame. Poser GC is a convenient way, but not the only one.

When I consider more detail in the darks the most relevant improvement to make the result look good without detailed postwork like curve adjustment and render passes, Poser GC is the way to go. Postwork instead requires the right adjustment curve and more, but is the most flexible, and the most efficient way to find the proper settings interactively. Tonemapping is an alternative that makes reducing the hilights as the most relevant improvement instead.

Take your pick.

You should have drawn all those with the final monitor gamma applied. Then only one is a straight line - the GC 2.2. Linear is a big bow down and looks bad. The others are reasonable as artistic choices as they deviate mildly from a stright line in useful ways.

In fact, I have been experimenting with a half dozen new color spaces that can be used before and after, the way gamma/antigamma is used. Some are nonsense, but some do interesting things that you cannot get with these.

The principle is that diffuse + reflection happens in the middle, and can be skewed to do non-linear (and sometimes useful) things by twisting and bending the color space first, doing something that is normally a straight line, and then restoring it afterward, imposing a curve on what you did.

When the monitor gamma is applied then indeed the G=2.2 curve becomes a straight line and the G=1.0 curve becomes a bow down, that's correct.

The G=1.0 image looks bad, that's correct too. But on the other hand, it's the best thing for input to serious post processing which of course requires the gamma correction embedding at some other point in the workflow.

Hence, whether G=1 or G=2.2 is the norm is just a matter of choice. I choose to confirm to your own (and wikipedia, and standard) graph where G=1 is a straight line, alike the photoshop 'do nothing' adjustment curve.

Happy Posing.

But if you use G=1.0 and export as non-HDR file, arent you're lacking the information to do a good GC in postwork? If you export as HDR or EXF you still have the nessesary information in the image, but these files are gamma corrected when you cut them down to a viewable dynamic range. 

Am I wrong here?

Why do you need gamma?

So you don't lose image information in a render and it displays properly.

Quote - But if you use G=1.0 and export as non-HDR file, arent you're lacking the information to do a good GC in postwork? If you export as HDR or EXF you still have the nessesary information in the image, but these files are gamma corrected when you cut them down to a viewable dynamic range. 

Am I wrong here?

I was hoping this would become clear that you're right without me having to do it. It seems I'm always being argumentative. But you're right. And I discussed this twice before in GC threads. I'm sorry but truth is truth.

There is the zero-data problem. A lot of your data maps to 0 - you cannot pull out anything from a pile of pixels full of zero. This is not just black - many colors have a component so close to 0 before gamma correction that they never come out right in postwork. And then there is banding - where many slightly different levels end up in the same integer.

Basically, the rule is you want to get the levels as close to their final values as possible before you export to 8-bit for postwork levels adjustment.

That usually means that the linear, uncorrected version is exactly not what you should tell people to use, artbee.

Demonstrations of zero data and banding are here:

http://www.renderosity.com/mod/forumpro/showthread.php?message_id=3652928&ebot_calc_page#message_3652928

Specifically...

Quote - The G=1.0 image looks bad, that's correct too. But on the other hand, it's the best thing for input to serious post processing which of course requires the gamma correction embedding at some other point in the workflow.

This is the part that is exactly dead wrong. It's the opposite of the correct advice.

There is another type of adjustment that I posted called HSV GC.

http://www.renderosity.com/mod/forumpro/showthread.php?message_id=3529805&ebot_calc_page#message_3529805

For those that don't have Poser Pro, and also do not want to deal with shader GC, and also recognize that postworked 8-bit GC leads to trouble, the artistic lens and HSV GC setup can give good results.

Here is a V4 portrait in original 8-bit uncorrected form, and then postwork corrected using HSV GC.

The banding and zero data problems are really easy to see here. (Click for full size)

HSV GC is an excellent way to change the fill lighting without washing out the colors. But it cannot do magic with the data lost in the original saved render.

Please note, however, that applying HSV GC in the render itself, using my artistic lens, does not suffer the data loss at all.

Note, however, that HDR and EXR file formats do not suffer the 8-bit data loss banding problem, and by definition are supposed to be gamma = 1.

So -

Quote - when you want to post process the image, especially when exporting to HDR or PSD or working with render passes in any other way, tonemapping as well as gamma should best be off

This is almost correct. It should say:

when you want to post process the image, only when exporting to HDR or 16-bit PSD or working with render passes in any other way using floating point or large integer formats, tonemapping as well as gamma should best be off

This article is excellent.

http://www.cambridgeincolour.com/tutorials/gamma-correction.htm

Especially read section 2. Look for the gradient showing 5-bit (32 level) encodings. By using a reduced bit depth, it easily demonstrates why gamma encoding your image results in more detail preserved for postwork.

Quote - Notice how the linear encoding uses insufficient levels to describe the dark tones — even though this leads to an excess of levels to describe the bright tones. On the other hand, the gamma encoded gradient distributes the tones roughly evenly across the entire range ("perceptually uniform"). This also ensures that subsequent image editing, color and histograms are all based on natural, perceptually uniform tones.

Also, what I was calling banding, they refer to as posterization. Read this.

http://www.cambridgeincolour.com/tutorials/posterization.htm

Quote - Any process which "stretches" the histogram has the potential to cause posterization. Stretching can be caused by techniques such as levels and curves in Photoshop, or by converting an image from one color space into another as part of color management. The best way to ward off posterization is to keep any histogram manipulation to a minimum.

Which is why I said that you should save an image as close to the final levels as possible. That's how you keep histogram manipulation to a minimum.

 That was me! I did exactly that. For whatever reason- these explanations and examples "clicked"- much appreciated BB and ArtBee for asking the question. I'm revisiting some previous renders. I was using a BB envirosphere and HDRI, GC OFF and trying to FIX things in the way you described. Blame 13 years of Poser Lighting compensation

Quote - Thanks Robyn.

Now here's where the wheels fall off for many people trying GC for the first time.

They start with a scene in which they manually compensated for gamma by adding lights and increasing light levels.

Then they flip on GC and don't do anything else. What happens?

This.

This is not because GC is on. It is because GC is on with overlighting, and all the numbers now mean something different, and the results are crazy bright. There is no dark side anymore.

Even this is not nearly so bright and zapped as many users experience. I'm starting with quality shaders that do not have Diffuse_Value = 1. I'm starting with specular that was set up correctly for the GC (accurate response) situation.

If I had started with no bias towards any of the best practices in CG, and was living in the Poserverse of 2003, turning on GC would seem like a horrible thing to do.

It's not. Rendering like it's 2003 is horrible. It's really limiting. You can't change things and just render. You have to tweak all over the place, and test and test and test.

Sorry I'm late to the thread and this won't contribute, but, I have been through all the gamma threads I have come across during my time here, and was able to understand and use GC so long as the contributing materials and textures weren't too messed up.  However it did not fully click for me until I read this post and specifically this paragraph (bagginsbill, Posted Tue, Oct 18, 2011 3:22 am): 

Quote - Now suppose you have a texture in which you have, using Photoshop, drawn a certain amount of red. As you made your drawing, you decided to use 89 red, because it looked right to you. Internally, you were making a decision to add more red until it looked right. What you were looking at was 10% red. What we want the renderer to use in its calculations involving this texture is that here it is 10% red. The way to do that is to "decode" the image. The image values are not linear. The value 89 means literally 10%. It does not mean 89/255 or 35% - it does not mean that at all. But if you ignore gamma, that's what you're using.

Thank you, bagginsbill. 

I don't understand why it would ever be suggested that adding gamma correction in post would ever be more "flexible" or whatever. Flat out common sense tells you that the more information you have in your image in the initial render, the better it is to work with in post. I don't need to have mastered the intricacies of GC to recognize that.

I would not say that adding gamma correction in post is more flexible, but working with HDR images in post is. HDR do have gc=1, so if you want to profit from the high number of light levels there, you have to do gc in postwork. The profit is in the HDR, not in GC postwork.

lots of fun, and anyone is right.

Gamma correction itself does not lead to any information loss, but exporting to 8 bit formats does. And indeed, if your interest is in the darker areas of the images, it's a good idea to boost these first before they fall into the zero/low-value-trap where the rounding has a large relative impact. Gamma first, export later.

On the other hand, exactly the opposite holds when you're doing cloudshapes in Vue: loosing the brightness details is the last thing you want. Export first, gamma later.

When combining Poser and Vue (or anything) in post, you have to color-match (aka: linearize) both components first, then work them, then decide on sacrificing either the darker or the lighter details. Also, importing the Poser results into other imaging programs require or favor linearized inputs, like Poser itself. Of course one can decide to gamma, to export, then to import and to anti-gamma as a serious way of work, but I suggest to keep up the resolution instead: 32 or 16 bits per color instead of 8, and no JPG.

And yes, exporting render passes to seperate diffuse, shadow, specular and eventually per-light and other layers into Photoshop enables me to manage (brighten, contrast, ...) each aspect seperately. Semi-dieu's Advanced Renderer (available at RDNA) offers a lot in this but just exporting to PSD with the proper layers tickers serve as a decent first step.

happy Posing, I'm out (I think)

I have uploaded an image to DeviantArt which I hope explains what is happening w.r.t. gamma correction.

The image shows only one part of the whole process (linear space -> sRGB) so it should easier to understand that the usual explanations which merge together both sides of the gamma correction process; in addition, graphs show what is happening in the linear color space.

Bye!!!