What is TONE MAPPING and WHITE POINT

Fauvist

I keep hearing it mentioned, but there seems to be tone mapping and white point meanings that are different than the ones for 3D renders.  Does anyone have an easy explaination for the 3D meaning?

Thanks!

grinch2901

I use the white point to correct for color in an image I don't want. For example some of my HDRI leave a yellow or orange hue to the image. If I set the white point to a similar yellow (or orange as the case may be) it tells the renderer to shift it's perception of color such that the yellow shade will be considered white and essentially it removes that shade from the image. Basically it gets rid of the tint I don't want. I don't know if I'm really using it right but I think that's more or less what it's doing in real life too.  You calibrate your camera to some object that is to be considered the reference white and it adjusts the colors accordingly except in a camera it's called "white balance".

But I'm not a photographer or a particularly good 3D artist so you may want to seek other opinions!

nemesis10

Fauvist said:

I keep hearing it mentioned, but there seems to be tone mapping and white point meanings that are different than the ones for 3D renders.  Does anyone have an easy explaination for the 3D meaning?

Thanks!

Imagine that you are watching a black and white movie.... there is a value for the darkest color, the brightest point (the white point) and the 50% grey.... when you adjust those, you are adjusting contrast.... So in a 3d scene, you rendere a scene as bright as you can while retaining the detail, choose the brightest value you want (the white point), choose the dark est you want, and then adjust the midrange to make a room that is blindingly bright or a gloomy near midnight or anything in between. That is one method of tone mapping as used in movies and tv where even night scenes are filled under very bright lights.  A second method is to render the scene under very bright conditions, very dark conditons, and something in between, and combine them using an image editor to create an hdr (high dynamic range) image where nothing is too bright or too dark.... I use Aurora https://aurorahdr.com to do this; the link will show some examples.  In iray, the HDRI backgrounds are the summation of a few images including bright bright sunlight, normal ambient light etc... so that they can act as light sources.

Joe Webb

Tonal Rage is very very handy for this. And if you apply the presets and review the Tone Mapping in the Render Settings editor, you get an idea of how things work.

Or you can just start messing with those settings. But I think the presets in that product are pretty good.

maclean

Tone Mapping is probably the most essential (and misunderstood) control for Iray. I keep hearing ppl talk about ramping lights up to billions of lumens for interiors. This is completely unnecessary. If you set Tone Mapping to a value for the scene, you shouldn't need to add more power to the lights. Remember that the default value of 13.0 is for a bright cloudy day - not indoor scenes. You can find a guide to the values here.

https://en.wikipedia.org/wiki/Exposure_value#Tabulated_exposure_values

As Grinch said, white point is used to correct color bias in HDRIs. Set it to the color you want to get rid of to get a neutral white tone..

jindracusin_b91ab57c9b

grinch2901 Your post is amazing since I have had too many people try to explain this in different ways that have made zero sense to me.  I am a photographer and a lot of the settings in DAZ don't correspond correctly to photography which is what makes no sense.  Your reference to what the white point is similiar to using a white balance color picker in Lightroom or Photoshop.  I never thought of it that way and as soon as I picked a pale yellow color, BAM! all my problems fixed.  I have been doing post edit corrections in Photoshop for every scene in.  

Again, the first post that really helped me answer this problem in DAZ

wiz

The "white point" is literally the "neutral point" for the color in an image. Any color "yellower than" the white point appears yellow, any color bluer than the white point appears blue. The whole scene could be lit by molten metal, which is so far into the yellow it's more orange or red. But if you adjust the white point to that exact molten metal color, the molten metal will appear clean neutral white. Anything slightly bluer than the molten metal (even if it appeared red in the scene, just a little less red than the molten metal) becomes bluish.

You have to be careful screwing around with white points. If the scene is outdoors on a relatively clear day you probably want "white colored" objects to look clean white, so yes, you set the white point to the same color as your light source. But if the scene is indoors and the lighting is "rustic" you want to set the white point bluer than the actual light color so things in the scene will look yellower or "warmer". Outdoors under cloudy skies you might deliberately set the white point too yellow, driving the scene a little into the blues and making everyting look colder.

Fishtales

There is another way to do it.

t the top right of the Viewport, beside where you choose a camera or view, is a small box divided in two with a small dot in the top right hand corner. One side is white with a + sign and the other is black with a - sign, I think, it is so small it is difficult to see. This is the White Balance/Exposure Tool. It has three settings, Exposure, White Balance and Both. You will find the settings in the Draw Settings Panel under Advanced with Draw Style set to Nvidia Iray.

To use it, I have mine set for White Balance. you click on it and move the cursor, which is now the little box, putting the black dot in the top right hand corner over any item that you want white, or at least the brightest grey. and click once. This will set the White Balance in Tone Mapping. If it comes out wrong or doesn't quite look right you can either set it back to the default and try again on another area or tweak the White Balance until you get the result you want.

You could also use a small plane in the scene set to mid grey, 128/128/128, like they do in photography and use that to set the White Balance.

https://www.pixelz.com/blog/need-accurate-color-let-grey-cards-white-balancing-come-rescue/

wiz

Tone mapping is rewriting the tonal relationships in an image to make it look different (hopefully better). It is an automatic version of the darkroom technique known as "burning and dodging". 

Every image has a range of tones (brightness levels). That range may be huge, i.e. anything that has deep shadows on a sunny day, or it may be small (a scene with diffuse lighting coming from everywhere and no objects that can catch shadows). You can adjust "tone curves" (which is what nemesis10 described, not "tone mapping") to move the scene's darkest color into a darker color in the output space (screen color or print color) and the lightes color into the lightest color of the output space, and then drag the middle anywhere you want it. When you move the scene's tonal limits "outward" (darkest into a darker place in the output, lighter place in the output) the scene looks more contrasty. When you move the scene's tones inward (image black becomes output dark grey, image white becomes output light gray) you reduce contrast. Moving the middle of the scene range to a brighter place in the output range gives the scene an overall increase in brightness, moving the middle tones to a darker place in the output range gives the scene an overall feeling of darkness.

That is basic stuff you could do in PhotoShop 25 since it first came out, other image editors, image viewers like Irfanview or XNView, you name it.

Tone mapping is something radicaly different. Imagine your scene has a huge tonal range. There's bright white things that reflect near 100% of sunlight (or an actual light source in the scene) and there's also super dark things (open windows into darkened rooms, hollow logs, etc). If you play with the simple "tone curve" enough to brighten the interior of that hollow log so that you can see the badger hiding inside, you've brightened the scene so much that the kid looking into the hollow log has been "blown out" into white. If you get the tones of the cloudy sky right you might have contracted the tone of the castle so it looks mostly a plain boring grey, when it really does have considerable texture.

So, the tone mapping algorithms starts playing with things "locally". It might "latch onto" the large, mostly gray areas of the castle, and start moving its tones around relative to each other so that the stonework acquires lots of "local contrast".

There isn't just one "tone mapping" algorithm, and they usually don't have simple controls. There are over a dozen popular ones, with names like Fattal, Rhinehardt, Manituk... Each has a different number of parameters, and each tends to do different things better. Like Fattal has two parameters mysteriously labeled "alpha" and "beta". Durand has three paramters: "base contrast", "spatial kernel sigma" and "range kernel sigma". People like DAZ, Adobe, etc. grab one or two of those algorithms, put more friendly names on the parameters like "mid  tone contrast" and bundle them into their software. If you really want to see a bit of awesomeness, have DAZ output an HDR format called EXR, and bring that into something that has lots of algorithms and keeps the original parameter names. There's a charming free program called Luminance HDR that gives you full control of 13 popular algorithms. It's available for real computers with Linux or Windows, and it's also available for Macs.

https://sourceforge.net/projects/qtpfsgui/