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I'd like to be able to tell where—and by how much—a highlight is blowing out without having to render, go into Photoshop, back into Blender, turn my lamp down, render etc etc. So I'm wondering, is there a way to do this within Blender, or even better, without the need to render first?

Danial
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1 Answers1

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Yes, press N in the image viewer to reveal the side panel and navigate to the Scopes tab.

In addition to the histogram, waveform, vector scope, and sample line found there, clicking on the image shows some useful information about the pixel under the cursor (in particular, the scene referred and display referred RGB values. Plus some fun things such as screen-space XYZ coordinates, where Z is depth).
You will have to render first to use these features, but you can use low-resolution, low sample test renders for fine-tuning.

enter image description here

You may also be interested in utilizing the wide dynamic range of the images cycles produces to help avoid re-rendering for small lighting changes. See How to put a Linear Workflow in practice with Cycles and Render with a wider dynamic range in cycles to produce photorealistic looking images

In old versions of blender (2.7x) the scopes were in the T panel on the other side.

gandalf3
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    If you are using cycles, use the Filmic Blender set of LUTs and OCIO config, you can use false color to visualize your light values before rendering. –  Dec 08 '16 at 06:38
  • Wow. I've been using Blender for months now and have never seen that panel. It doesn't seem to be working properly, however. The Histogram is blank, as is the Vectorscope. The Waveform is showing something... even though I don't know how to read it. – Danial Dec 08 '16 at 06:44
  • Another way to know the scene referred values and how they are being transformed to Display referred is by clicking over the image. A set of numbers will appear at the bottom: http://i.stack.imgur.com/8CR2C.gif Showing the value for a given pixel in each of the RGB channels. –  Dec 08 '16 at 06:44
  • See also: http://blender.stackexchange.com/questions/67357/scene-referred-and-display-referred-rgb-values-of-the-image –  Dec 08 '16 at 06:46
  • Sadly the histogram(or the waveform monitor) will not show you values that exceed the 0 to 1 range of display referred images, –  Dec 08 '16 at 06:48
  • @cegaton It's not showing me anything at the moment. – Danial Dec 08 '16 at 06:56
  • How do we see the RGB/XYZ info in Blender 2.8? – SO_fix_the_vote_sorting_bug Mar 18 '19 at 15:38
  • @jdk1.0 Nothing has changed, as far as I can tell? – gandalf3 Mar 19 '19 at 01:33
  • @gandalf3 Maybe I need to update to the latest beta because I can't see that info. – SO_fix_the_vote_sorting_bug Mar 22 '19 at 11:24
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    @HarryMcKenzie Updated it, thanks for the heads up! – gandalf3 Sep 07 '23 at 00:41