well i don’t really know where to post this, maybe the support subforum would been more appropriate but well…
i downloaded some material galleries and i think it’s a common practice that i strongly disagree and would like some comment about it.
the diffuse reflection commonly used is 0.8 which is quite high already for nature.
i also see even higher values received for metals ( 1.0 ???) meaning all the light is diffused, very very unnatural…
even more lower values aren’t used…
and also materials that are matt have specular values.
i could post an extract from the 3ds max manual, i don’t know if that’s permitted, where you could read that for wood as an example the highest value for reflection is .7 and as low as .5.
i’m waiting comments
Yes, you are right. In reality no object can emit more than 100% of the light received. Leigh Van Der Byl has written an article about this issue. Unfortunatly it`s no longer availible, so I loaded it up again.
thanks for posting the link, it looks like a very complete guide.
Three things I most often find wrong with materials when people are going for believability:
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Saturation of color is way too high. Use the HSV sliders instead of RGB, and keep the S as low as you can bear.
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Ref value is too high. If you reduce the ref value, not only is it more realistic, but you’ll find that you have to up your lights a bit too. That’ll actually give you more light “energy” to play with in the scene, and let you have a greater range of contrast for visual interest
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Spec too high. Unless you can really see the highlight on that object in your mind’s eye, consider setting Spec to 0. Nice effects can be achieved by setting spec to a relatively low value (0.1), then reducing hardness to somewhere between 5 and 10 – this gives the effect of boosting your material’s overall sensitivity to light.
i also see people ignoring ambient light, or setting material to not get any, which is impossible unless it is in a black box or completely unlit room. Receiving ambient helps flatten out the color saturation, as harkyman (with highly oversaturated eyes) commented.
I also think (and I will shutup now) that most people overlight their scenes, or ignore lighting alltogether, resulting in them having to set these values in extremis so that it ‘looks right’ in the render.
I think we should also note that in a virtual playground, we can make any color or surface do anything we want to, and end up with avant guarde imagery. Which is cool too, I mean, why be bound by reality?
I think the Blender Material Library is good, and we should try building on/improving that.
I’ll SHUT UP now and go to bed.
talking about refl. no reflection reflects the surrounding color 100% !!!
all reflections are tinted!
Another problem; the capability of individual screens. Analog screens seem to have more accurate contrast, at least in my experience, and digital flat panels have colors that are probably more precise. I really don’t know actually what the difference is, but it’s there. Designing images that display well on all monitors is difficult. What looks good on my ten year old 14" interlaced screen may have a much different look on the 1300mm 1080p wrap-around screen you have at your work station.
And then, of course, if you’re printing, saturation is just again an all together different approach.
first of all thank you for replying, and i would like more people to join this conversation, and maybe some of the yafray guys and users…
to rogerwickes: yes you are right,we are talking about cg and we shouldn’t be bound to reality but when we want to, and when a material library is out i think it should be bound to reality… if you want to achieve an effect you could play with other values, i mean a stone material with high specular value? come on, you hardly ever find a stone in nature with specular.
Callibrating your Monitor could help. A ten year old 14" interlaced screen is only crap. Make a aquarium out of it :D.
Absolutely agree. Why create a material implying that it is one thing when it really is another? I would add that from a psych standpoint, people want their pictures to be spectactular (get it?), so human nature may be partly to blame, coupled with ignorance and haste and different display devices and paper quality…
Let’s keep this thread going, and I will make a wiki section to guide users in defining materials.
Hi i had to quote before i could post to this interesting discussion ( somthing is wrong with the log in at this forum )
Blender is thought mainly for animation and not for photo-realistic rendering … that’s why the materials are like the are having for example specular value … specular is in reality reflection but for a scanline render that needs to produce alot of images for a animation , it would take too long to produce real “blurry” refection … so they fake the blurry reflection with this specular value and hardness ( in other words the surface roughness properties ) and only sample the light and not the rest of the scene …
specular = reflection ( Blender only offers faked specular )
Greetings Patrick
Patricks. I think he means you never find a stone out in nature that’s glossy and shiny like plastic, he said ‘HIGH specular’. 
i did not want to quot him … but i could only post if i quot another post … there seem to be some problems here at the forum when log in and wanting to post … this time it worked without quoting …
so my post was meant in general that specular is in reality reflection and that Blenders specularity is fake specularity/reflection …
Greetings Patrick
i also see people ignoring ambient light
Ambient light is discouraged in every professional writting about lighting and shading I’ve read so far.
If he means using the Ambient setting, then yes. But it’s true that people ignore the effect of true ambient lighting in their renders… It’s easy to fake outdoors with a sun lamp and properly tuned AO using sky texture and a good sky map. Inside its tougher to do, and you have to sometimes make fairly complex lamp setups.
Well, that’s if you’re using Blender internal. If you’re using Yafray, that’s taken care of for you!