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ok this title sounds maybe a bit weird so let me explain first. The gold standard for colon examination is the colonoscopy, so a camera inside you. But the problem is you can't say the camera pose (location + orientation) at any time. Thank you, there is Blender, so I try from a CT scan to simulate a colonoscopy with Blender. It is working good so far, the CT scan is transformed in a pretty good blender-model and the animation is done.

For this a attached a spot light to my camera, it is pointing in the same direction, like in a real scenario. In generall it is fine, but I want to make it as real as possible. So lets have a look on a real colonoscopy image and my rendered image, before we go ahead.

This is how a real image looks like, it is a random source from the internet

And here is one cycle rendered image: Rendered Colon

Those two images will never look the same, because there are no texture informations for blender and there never will be. So please ignore texture details like veins and so on. Even the red color which is made from a simple material is not important. But my point is to get the most realistic light, shadow, reflections as possible in this image. I am newbie and using Blender 2.79b (because of a tutorial), here are my questions:

I need to know if it's better to import the actual settings of the real fisheye camera or simulate it as close as possible wwith Blender. And currently I am using a spotlight, with a size of 2, max bounces of 50 and white color. But how go I get any specular light reflection at all (Except in the other renderers blender and blender game)? I cannot even find an option for the brightness of the spotlight.

If you have any other tipp or reference to improve the quality of my simulation, I would be pretty grateful.

BR Amgebee

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    $\begingroup$ Hi. I'd like to help, but the link to the image of a "real colon" seems to be broken. Could you try re-uploading it? $\endgroup$ – Christopher Bennett Jul 16 at 8:10
  • $\begingroup$ (...thankfully...) $\endgroup$ – Strawberry Jul 16 at 9:00
  • $\begingroup$ I've updated the link - sorry @Strawberry ;-) I've left it as a link rather than an embedded image so people only see it if clicked on (they might be eating at the time...) $\endgroup$ – Rich Sedman Jul 16 at 9:06
  • $\begingroup$ Reflections also depend on the material the light falls on. $\endgroup$ – Luciano Jul 16 at 9:11
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To answer your question about the camera, you could do either. Try inputting the specifications of the camera you are using, and see if it looks right, otherwise I would recommend Panoramic set to Fisheye Equisolid. You can play with the aperture and FOV settings from there.

For the material/ reflections, you can try this:

ColonShader

Basically What I did was warp the vectors of a couple of Voronai Textures with a noise texture that I softened by mixing it heavily with light grey. I offset one of them, and colored them red and blue respectively, to make the veins. I also attempted to cancel some of the vein continuity by mixing in another Noise Texture, but looking at it now, I think I needed to darken the noise with a ColorRamp first.

Veins

I made the wall color by connecting a ColorRamp to another noise texture, and used a Musgrave Texture to make the inner wall bumps. I softened the Musgrave and plugged it into the height input of a bump node to get some normal information. Before this, I mixed in some height information from the veins as well. I also inverted this mix and darkened the contrast to use as a roughness input - this, combined with the normal map is a large basis for the reflections. Lastly I mixed the colors together to use as both the BaseColor and the Subsurface color.

ColonMix

I set my Principled BDSF as shown below. I made this in EEVEE, but it works just as well in Cycles - just note that you may have to turn down the transmission, subsurface, and maybe even metallic to make it look correct.

ColonShaderSetup

The end result looks like this:

ColonFinal

I'll upload the blend file if you want to see for yourself - Keep in mind this is for 2.83, so it will likely not work in 2.79 unfortunately due to my use of Vector Math nodes, which I think 2.79 may lack (correct me if i'm wrong). If you can obtain and use 2.83, I would heavily recommend it.

File is here -

Cheers

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  • $\begingroup$ Thank you a lot for the very specific and very very fast answer. I guess it will take me days to understand this, because I just started blender. I couldn't image make it look like yours or that this is even possible. This looks awesome!!! $\endgroup$ – AMGEBEE Jul 16 at 12:27

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