Author Topic: Surfaces of slightly recessed buttons darker accross entire surface  (Read 1137 times)

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Offline sdesaulles

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I'm not sure quite how to describe this, but generally, KeyShot seems to do a good job, but what seems like a very simple render seems to cause it (or me) problems. I'm working on a simple medical device - pretty much all white and with a subtly recessed flat button in a flat surface, but that recess seems to cause a universal darkening of the button top surface regardless how wide it is.  I've done a "test block" to demonstrate the issue.

Having searched the forum can't seem to find anyone asking the same thing, its really simple, and goes like this.

I have a 30mm diameter button that is flush with the main surface, made of the same material, everything renders fine, it is identical tonally to that main top surface.
That same button, if recessed by just 0.4mm becomes darker than the top surface across its entire surface. It just looks like its a darker material.
PTC Creo's default renderer seems to render it as I would expect, a highlight/lowlight for the surrounding 1.0mm x 0.4mm chamfer, but the slightly recessed surface almost exactly the same tone as the main block.

I have tried making the buttons from the same block, or as separate entities, makes no difference. I'm using the standard "startup HDR" environment, white gloss plastic. 

Package attached.

As another test, I made a disk with revolved steps, to see if there was a perceptible darkening on each step, no, just the uppermost surface is white, all lower "step tops" are the same shade of grey - looking like a different material.

Thoughts welcome. I would seem to have to select a grey for the body and white buttons to try to tone match - not exactly sophisticated, but gets a bit closer. Tried turning on global illumination, it helps a bit, but then makes the button split lines glow as if there's a light source inside the block.

Thanks

Stephen

Offline DMerz III

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 ??? Strange phenomenon indeed.

Curious, do you experience this same effect if you turn off the HDRI and use a physical light instead? (Area light, spotlight, etc.)

Offline RRIS

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Hm, do you have the same problem when you increase shadow quality (or disable self-shadows?).

Offline jet1990

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Perhaps if the light source is perpendicular to the model than what you're getting is effectively a shadow cast on the shallow regions of the recess. Change the light environment and have a light shine downwards at an angle to see if that helps?

Offline jet1990

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i downloaded the model and had a play with it. Please note the big button on the far right. By adjusting the depth of it you create more of a shadow on the entire surface.

Offline sdesaulles

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Thank you all for the responses and suggestions.

Adding point lights within the environment, directly pointing at the darker surface makes a slight difference, but not much. (not sure how to add an "Area light", and the help wasn't much help, seemed to suggest I could just create a new object and turn it into a light source using a "lightbulb" icon in the "Scene" panel, but not sure where that "light switch" is.)
Switching off "self shadows" definitely solves it, but the downside is that KeyShot 8 then creates such a poor render that I'm better off with a Creo screen grab.

Yes, lifting the button on the right (as you suggested, jet1990) improves things, I tried something similar, adding a small upstand lip all around the main block, that then improves what happens on the buttons, but I then have an extra part of the model to photoshop out - doh!
Switching on interior mode seems to get the closest to "reality" that I have found so far, but there is still a distinctly darker tone to the sub-flush buttons.

Thanks again for your thoughts ... I will continue to experiment. Meanwhile, KeyShot 8 seems to be half crashing almost all the time, hangs on save for minutes at a time even on this simple file. Tried total re-install, still the same. KeyShot 6 with the same file saves in about a second.

Stephen

Offline sleby

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I am pretty sure that is because the scene is lit not only from directly above but from the sides as well and that's the shadow what you are looking at.
Create new environment and manually light the scene with area light from above (edit-add geometry, apply some light material from materials library - if nothing happens increase the power) and you'll see if that was really the problem. Then you can go back to your default scene and just add another light from above to help remove the shadows (the same way as before or in hdri editor).

EDIT:
I opened image jet1990 posted in photoshop and noticed a strange phenomenon.. all 3 buttons are the same brightness. The shadow on the edge creates an illusion that the recessed buttons are darker than flushed one. Human brains really are a strange thing:)
« Last Edit: May 29, 2019, 04:35:42 am by sleby »

Offline Esben Oxholm

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EDIT:
I opened image jet1990 posted in photoshop and noticed a strange phenomenon.. all 3 buttons are the same brightness. The shadow on the edge creates an illusion that the recessed buttons are darker than flushed one. Human brains really are a strange thing:)

Good catch. I too think our brains are tricking us to 'see' the recessed button as more dark than it really is. The fact that it's recessed and is contrasted by the highlight on the edge chamfer makes it look less bright.
I took the color picker in photoshop over the center of the three buttons (just to double check) and the center of the left and center button is actually the exact same value while the right is brighter by only 1%.

I think you've created a subtle version of this optical illusion: https://news.bbcimg.co.uk/nol/shared/bsp/hi/dhtml_slides/10/illusion3/img/illusion_dhtml_6_v2.gif
The 'brown' square on the top is the exact same color as the 'orange' on the side in the shadow (and the 'brown' on the ground as well).

On another hand, I think it makes sense that the recessed button is darker with the light coming from the right. Subtle occlusion shadow will cover some of the area.

Might not be the entire answer, but at least an influence on the result.