Gamma Correction
Szark
Posts: 10,634
Can someone help me to understand what the Gamma correction ON/Off function in the render settings if for.
I understand what Gamma is that is not the issue and that in the Surfaces Pane we have Image Editor and a value of 0.00 means automatic Gamma of the texture map is detected so why do we need this Gamma ON/OFF function. I just can't get my head around the Why if the Gamma is detected automatically.
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I don't really know what is done inside DS but I'll guess that for textures that are not Gamma encoded you may get false results (aka old products?). And I'm not sure everybody encodes textures with the correct Gamma and before that calibrate the monitor as it should.
You could also correct the textures yourself and not wanting them to be messed.
As I see it Gamma as standard for textures made in, for example Photoshop are at 2.2 where the older version of DS used a Gamma of 1.0 so I can understand that automatic detection of a Gamma gives you the best possible representation of the textures now.
I just can't see why but as you say Takeo it could be for that but this is a blanket command not an individual texture by texture function which is why I posed the question.
I am not getting messed results but more from the POV I want to understand the "why" and "what" this would be used for on a scene basis.
Thank you for trying though Takeo it is appreciated.
This automatic guessing and the gamma setting in the image editor only has effect with gamma set to ON. With set to OFF, it always uses 1.
Sweet thanks millighost.. I just wondered why the big diffrence in renders when ON or OFF. Seems I need to think/learn about texture maps a bit more. Good result thanks guys.
Gamma 1 is generally appropriate fro control maps - opacity, bump, displacement and so on - where the colour or grey level represents something specific.
Gamma 2.2 is generally appropriate for diffuse colour, and probably other colours, where the colours are picked by eye (or come from a visually adjusted photo) to look right on a figure and so probably have the monitor gamma built in.
Thanks Richard I did read that bump maps etc where best with a Gamma of 1 and the diffuse maps 2.2 and that Photoshop 5 and above save everything at 2.2 and that with me seeing it on a monitor that isn't callibrated etc could explain why, when all the diffuse maps we at 0.00 in the Image Editor and Gamma Correction Turned ON, I was getting darker renders when increasing Gamma makes things lighter (as far I know) has me a bit preplexed I am just testing everything these days and I got around to this aspect and I seroiuosly want to completley understand how it works, or should work. So I now have how it works now I need to learn why I get the darker renders.
Photoshop has, for a good many versions (since 6, not CS6, I think) had a working space that can have any desired gamma (but usually 2.2) and then uses the screen profile to, hopefully, render that accurately on the monitor. But that isn't really relevant as people will usually adjust their textures until they look right in Poser/DS, not so that they look right as bearskin rugs in PS.
This is true most will just adjust as how they see it etc so hence me wondering why we have this function in Daz Studio and why we needed it as in what context is this function needed.
OK thought you asked why DAZ included the On/Off button. Didn't understand you wanted to know the why of Gamma correction
The reason is that 3delight like any other renderers calculate in linear space (Gamma = 1)
Our monitors are around gamma 2.2 because our eyes can't make any difference in colors in bright values but are better in lower range. So they are adjusted to our eyes
So without Gamma correction you send a darker image to the render engine. If you want a correct color, you should correct your image to gamma 1 (which should make it brighter) before sending it to the render engine After the render is finished you get an image at gamma 1. At that point you should correct the rendered image to gamma 2.2 in order to get is correct on the monitor (which make it again darker)
If everything in the process is correctely done, then the only question is : do we have correct textures?
Of course all of these is only for colored textures not the grayscale one
Thanks Takeo what was throwing me is that you said lowering gamma from 2.2 to 1.0 makes the map lighter and I always thought if you decrease the gamma you get a darker more richer coloured map not lighter. which in fact it is the reverse of that. This http://www.cambridgeincolour.com/tutorials/gamma-correction.htm was a great help too but you pushed me wanting to know more so thank for that nudge. I have no idea why I thought the reverse but I am better know. Why don't peolpe say the simple thing of "it makes the rendered colours look like you would see with your eyes and not through any imaging device". ;)
at least I wasn''t alone. ;) http://www.daz3d.com/forums/discussion/25644/
Ok in fact what you though applies to exposure. So you're a Gamma specialist now and can make us a tutorial ?
LOL I wouldn't go that far but I now understand a lot more and putting it in plain english is the hard part. Yes you were right I needed to understand what Gamma (in this context) is completely before understanding why we have this correction on/off in Daz Studio
The button is slightly confusing as the render is always corrected to the given gamma - what the button does is turn on the removal of the correction on the input images. If it is off, and you have the render gamma set to 2.2, the images are effectively corrected twice (once at their creation and then on the render output) and that's why they come out washed out and overexposed looking.
Thanks Richard. Yeah that is what I figured when I woke up this morning so it is starting to make sense....finally. I did play with the gamma slider and saw the washout out diffuse last night.
I've been meaning to experiment with this (there's always another thing to learn, isn't there?)...
In addition to the Carrara thread linked to above, this thread might be of interest.
@Scott : I saw the thread, but didn't really follow it. It doesn't really surprised me that people get more correct renders with Gamma correction. What did surprise me rather is that people just begin to do it with DS Products
How do we know when a texture map is Gamma Callibrated. Yes we can presume everything out of Photoshop is and any digital image not in RAW format is, so with that can we correctly assume every map is? Also how can we check?
I think that is one of the problems. Usually I am actually getting - in my view - better results w/o gamma correction features, especially on trans maps, which outright look weird at times as soon as I dabble with the gamma correction features. That may be partially due to these features not being available in DAZ Studio for long, which could mean that many DAZ Studio textures/materials are actually aimed at not to be used with said features. This is pure guesswork of course, but I am avoiding the gamma correction for the time being.
Indeed hence my original question of context, when and when not to use GC.
You tell by how it looks - unless it has a colour profile attached.
As for transmaps, if they go weird try using the Image editor option to set the gamma to 1.0 - control maps should not normally require adjustment since they represent values rather than colours (a possible exception being coloured opacity maps, but if they were made by inverting the presumably corrected diffuse map they'd want anti-correction rather than standard correction).
I know that I am able to alter the gamma correction on a per image level, but that is usually not something I want to dabble with - takes too much time really and you can't really tell until you render as to if and how you need to correct. The trans maps in question are from some older, originally designed for Poser hair and turn out rather "thin" as soon as the On/Off switch is turned. In essence I leave everything to default due to that and also because I actually think that it looks better. I lived until about DAZ Studio 4.5 (or 4.6) with default, so I might as well live a couple years more with it ;)
This just function doesn't make much sense to me at all. I understand why we have Gamma correction in the first place that is not the issue. The issue is when does this come in to play in general rendering, that is what I need to understand.
If it is a case of asthetics then fine I can live with that, but somehow I don't feel it is.
If the map was set to look right without ay gamma correction (to the image or to the final render) then it probably needs to be corrected if you do have a final render other than 1. Only maps that were created to look right in Poser or DS with gamma correction applied to both final render and textures are likely to be gamma 1 and so not require render-time correction.
I do appreciate your help Richard and always have but I am just not getting how we know when to use GC or not. Yeah it maybe down to me being on the thick side or just a lack of general knowledge of digitaly made images but I am just not getting it. :)
Oh and I am not being difficult as there is a very good reason why I need to completely understand this, reasons I can't go in to now.
Does anyone have any any links to help me understand this better, in plain English. ;)
If in doubt, apply a GC of 2.2 to colour maps (though, especially diffuse colour, which render as colours on the model, rather than those such as opacity or bump, which control other properties and don't show up directly in the render. That will rarely be wrong.
Do you mean setting the diffuse to 2.2 in the image editor that is in the surface pane? I Photoshop CS2 I don't seem the have a Gamma setting, well not in this sense. I have exposure Gamma settings which is different.
I have tested setting the difffuse to 2.2 and kept the render settings gamma at 1 and the diffuse came out really dark.