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drawovis

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Reply with quote  #1 
I worked on different projects with Prowalker for a while and happened to come across some color issues. Especially in the reddish colors.

Perhaps I've missed a basic tutorial here, but this is what I often do:
When I want to use just a color (as used in a logo), I open the image with Photoshop and pick up the RGB value. I use that value to make a material (no texture) with that RGB value. But then often in the PW renders the colors was quite different from what I expected.

SU-colortesting.jpg 
So I did a little test, I inserted the logo and exploded the image, I gave a block the RGB value from Ps. Then rendered with Prowalker and Podium 2.6. (no HDRI images as background, of course)

ProWalker-color-testing 1.png   
Podium color-testing 1.png 

The results strike me as strange, it seems that PW got the color of the logo oke, but the RGB values are wrong.
Podium seems to get color the logo off, but it compares with the RGB value of the block.

To get more comparison I added a Red color from the left chart and gave the block that RGB value. There Podium seems to get it more right then PW.
I suppose it all has to do with render engines, but if someone could clarify this, I would be thankful.

The workaround seems to be simple; If you want the exact color in your render, use a colored texture as material. (in this case the logo).
So the lesson I've learned here is to never use just RGB colors as material in render engines, but always textures?
I attached the SU file and the logo for your testing. I would like to hear your comments/advice.
Prowalker color-testing texture 2.png 
Podium color-testing 2.png 





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png image.png (4.69 KB, 4 views)

 
Attached Files
skp color-testing.skp (1.46 MB, 3 views)

JustinSlick

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Reply with quote  #2 
Wow that's crazy, the 234-0-42 example isn't even close.

Only thing I can think of is some kind of color cast from the sky simulation. Look what happens when you layer a light blue color over the 234-0-42 tone:

Color overlay

Resulting tone is very similar to what you've shown in the render.

It's really interesting that the color representation is pretty much perfect when you use a texture though.

I'm curious if other pathtracers behave the same way -- I might try the same test in Cycles and see if the result is similar.

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JustinSlick

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Reply with quote  #3 

So I tried it with Cycles, which is very similar to Iray under the hood.  I think the same basic behavior is present:

Neutral background with white light -- Color representation is pretty accurate, but sort of dulled by the gray background I think.

[cycles-neutral] 

Blue tinted sky simulation -- Color shift toward fuschia, similar to ProWalker

[cycles-skysim] 

Lit with Afternoon 1 HDRI from Prowalker  -- Color representation looks pretty good to me.  This might be closest to the original color swatch?

[cycles-hdri] 


On some level, I think this is just an inherent mannerism of raytracing/pathtracing.  That is, lighting matters a lot with solid colored surfaces.

The fact that using a texture file instead of an RGB value yields more accurate color is really interesting though.  I don't have any idea why that's the case, but I think that's a really valuable tip you discovered.


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JustinSlick

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Reply with quote  #4 
I will say -- the ProWalker example you've shown is probably the worst result of any of these.  It makes me think the color gradient of the ProWalker physical sky simulations is far too saturated or something like that.

I wonder if we could dial this in by toning down the color in the sky simulations.  I admit I hardly ever use them, because they usually don't feel as natural as HDRI to me.  But of course sometimes you need the accurate shadow placement.

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bigstick

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Reply with quote  #5 
All the Farrow & Ball colours in the browser are actually just RGB colours, and generally they look pretty good.

At least that's what my wife tells me because she paints and has been mixing colours since she was about 5!
I'm strongly red/green colour blind, I can see the colour variations in the images, but I couldn't tell you what those colours are and how the hue is different [rolleyes]

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drawovis

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Reply with quote  #6 
Thanks Justin,
Just a short reply, before I got to finish a big render order today.
I've tried Podium with Afternoon1.HDR but I still get the off-color.
color-testing 2020-03-13 09220500000.png 
And in PW with afternoon1.HDR I get this:
PWc-olor-testing-HDRI-Afternoon1.png 
and in PW with a grey sky, like Winterlake01.HDR I get this:
PWc-olor-testing-HDRI-winterlake01.png 
Justin, did you use my model? (I hope that all the fuzz is not because I've made some stupid mistake...[frown] )


JustinSlick

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Reply with quote  #7 
Quote:
Justin, did you use my model? (I hope that all the fuzz is not because I've made some stupid mistake...[frown] )


Nah my tests were done in Blender because I wanted to see if a different (but very similar) render engine would show the same shortcomings.  Which, I think it did to some extent.

It's definitely not something you're doing wrong, I'm getting the same inaccurate colors when I test in ProWaker.  I guess using a texture instead of RGB is the best workaround for now.

I thought this one from Podium was pretty good at least.... 234-0-42 seems very close on my monitor.color-testing 2020-03-13 09220500000.png


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drawovis

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Reply with quote  #8 

I extended the test a little bit more, to see if you could use any RGB texture for this.
scrndmp-SU.png 

so I made a grey texture and changed it to red, green and blue with the color edit in SU. No problem there.
Then I took a green texture and changed that to red and blue and even to a Farrow&Ball color.
Also no problem. So it seems it doesn't matter what RGB texture you use, you can adjust the RGB color in SU and get the result right.
The block below is from the Browser with only the RGB code attached.

Here's the render in ProWalker, afternoon1.HDR
color-testing2.png

 
Attached Files
skp color-testing2.skp (4.38 MB, 0 views)

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