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Total beginner to Blender here, so please pardon my general ignorance.

I'm trying to render product shots of some photographic prints for my wife. I've bought an interior scene from evermotion which already had some prints on the wall, and am trying to substitute her photos for those prints.

To do this, I've deleted the meshes for the existing prints (they were using a texture atlas for all of the prints, which seemed like unnecessary additional complexity for now), added in planes for the new prints, and used a simple "image texture" material on them. This approximately works, but the photos look over exposed when I render -- this is the problem I'm trying to solve.

Moreover, I'm a bit confused about what's actually happening: she sent me JPEGs of developed RAW files which had already had exposure, tone-mapping, gamma, etc applied in Lightroom. My understanding of 3D graphics was that you generally wanted to work on linear data and then apply the tone-map and gamma to the final render. So I guess I'm not surprised that it's come out wrong, but I'm at a bit of a loss to understand the best path to making it "right".

Would appreciate any pointers on this! Thanks!

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  • $\begingroup$ is hard to say without an example. you could check if in the scene properties under the color management your render view is on Filmic. it may help lowering down the exposure $\endgroup$ – Virgil Sisoe Nov 12 '18 at 20:59
  • $\begingroup$ Thanks Virgil. The render is already set to Filmic. What info would you need to help diagnose this? I'm still at the stage of just stumbling through the UI, but can try to find stuff if you can give me an idea of what to look for. $\endgroup$ – j4m3z0r Nov 12 '18 at 23:10
  • $\begingroup$ well there are a lot of things that could add to the over exposure in the final render. it depends if you are using the Cycles render engine or the Blender Internal render. it may depend on your material and the position of the lights and so on. so usually the more you can let us know the better. if you don't want to share the render try other jpeg images and see if you get the same result and if yes then show them. $\endgroup$ – Virgil Sisoe Nov 12 '18 at 23:29
  • $\begingroup$ Ok, got it. It occurred to me that I should look at the materials that the original used and see if I can replicate that. So I'll have a go at that first. If I can't figure it out with that, I'll share some screenshots. And I'm using Cycles, FWIW. $\endgroup$ – j4m3z0r Nov 13 '18 at 0:32
  • $\begingroup$ Ok, so I think here's what's happening: the original scene specified Exposure 1.6 in the Color Management section of the scene properties. Reducing that to 0 gets the prints back to the expected exposure but of course then the rest of the scene is too dark. I can think of 3 potential paths forward: 1. Change the material on the prints to apply -1.6 stops of exposure adjustment... somehow. 2. Remove the scene's 1.6 stops and play with the lights to get more light in the scene. 3. Somehow change the material for the prints to something that ignores the lighting and just sends back texels. $\endgroup$ – j4m3z0r Nov 13 '18 at 1:30
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Ok, here's what I ended up doing. Thank you @virgil-sisoe for the pointers.

First up, I may have been overly concerned about gamma correction: it looks like Blender automatically gamma "uncorrects" (wrongs?) texture data when it's loaded, so the output of the texture node can be assumed to be linear.

From there I added a "Separate RGB" node, and added a Multiply node on each of its 3 outputs, followed by a "Combine RGB" node. I set each of the multiply nodes to 0.5, so -1 stop.

(arguably it should have been -1.6 stops, but -1 looked right given the brightness of the rest of the scene).

I added gamma nodes to the input and output, but have the input gamma set to 1 (so no gamma adjustment), and the output a little over 1 to add just a touch of contrast.

The last thing I did was to switch from the principled BSDF shader to the diffuse BSDF shader. I figured that I only want diffuse here, and I don't yet fully understand the principled shader.

This looks ok, and I think it will suffice for my current purposes.

Here's what I ended up with:

Material setup

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