Linear Workflow in 3DSMax and VRay

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Aug 31, 2005

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3dsmax Versions:

7.x, 8.x

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Users of other apps/renderers, I am starting to put pertinent info at the bottom of the page

Have you ever wondered why your GI renderings start out so dark? Well, in fact they are not so dark. The problem lies with the display device (the CRT or LCD) and that the software is not making adjustments for the gamma that the displays put on our images. That gamma is specifically called �sRGB. Technical information about sRGB can be found at that site.

Let's take a look at what your monitor does to image data you send it. This is called non-linear a display. The spotted green line here is the data you are feeding the display and the solid green line is what response the monitor has normally.

What's important to note here is that this correction is not just for filmic response. In fact, it has almost nothing to do with filmic response. It's essentially correcting for the display. Those of you working for video (aka not film) don't worry. This applies to you as well. The rec.709 curve is -very- similar in nature.



Ok, that's nice and all but now you want to know how to solve this problem. Yes, it's a problem :) Well, friends, we apply a curve that takes the data and "linearizes" it. That means we negate what the monitor does. Here is the curve. Once again, the spotted line is the data we are sending to the display. The solid line, this time, is the correction that's made for the non-linear display.



To explain a bit further...sRGB is the correction your software makes for the non-linear response that your monitor has. Your digital camera applies an sRGB lookup to your photographs but you may not even know it. So, when you work in true linear space you are actually working in a space that represents more what light does in the real world. Let's show you what I mean by that with yet more graphs but with a gradient this time.



This is a 0 to 1 ramp with 32 steps. Notice the 0.5 value is in the middle. This is the original image data as sent to your monitor. This is a linear image!



This is what your monitor does to the image. The .5 we had before is certainly not .5 anymore. This is your non-linear monitor.



This is the correction we put on our viewing system to correct for the monitor's display. Yes it's much brighter. However, this is needed to correct for image #2 which makes the display turn your gradient back into the original linear image.
Hopefully that makes a bit more sense

Keeping on with the flow of information, check out another test to show you what linear is all about.

Here are two images. The grey swatch in the center or each image has a value of .18 (the mid grey point) in the 3D app. The one on the left is gamma encoded to sRGB, where the one on the right is linearized via the sRGB monitor correction. This turns the grey into .46 which is the spec for sRGB.

Gamma Encoded image Notice the total lack of shadow detail


Linearized Image Notice the amount of detail we gain!


If you want to get a copy of the max file (it's using vray but doesn't require it) go here: sRGB_Linear_demo.zip

Let's get into the meat of the 3D app in question : 3DS Max 7.0 and VRay 1.46.xx.

For this example I have provided a scene that I used for testing : linear_demo.zip

Here is a scene prepped for Brazil by Rune Spaans : linear_demo_brazil.zip

You will need the �Greeble plugin to properly open this scene.

The first result we get from this render is so:

click for larger version

Now, we must linearize this image if we are to get more of a photographic response. What am I talking about? Well, look at the amount of light hitting those objects. It seems that with 1000 GI bounces that we'd see a bit more detail right?!? YES! Let's get to that stage now.
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Mar 02, 2011
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thanks you!! very good you are master

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