Depth of colour

[Peter Milner]

Speaking with our graphic designer it appears that renderings have a lot less colour depth than photos.

This limits the amount he can tweak an image in Photoshop.

The result is that in publications, renders tend to look flatter and not as vibrant as photos.

Is this a limitation of the software?

[Roy Hirshkowitz]

Perhaps.  It's hard to say, without looking at specific examples, where the problem lies.

 

If this is a tone-mapping issue (it isn't necessarily) you can try a few things:

 

1. You can save an image in an hdr format and see if you get better results using a tone-mapping in an hdr editor (including Photoshop.)
2. You can try messing with the histogram in the Image Editor-- the idea is to get the thing to broaden-- by using the Brightness and Burn settings.
3. You can try using histogram equalization or the histo/curves controls in a tone-mapped image-- this can sometimes work.

 

The issue can also arise from calculation problems.  For example, our materials use RGB internally.  It's better if we had many more data points-- sometimes called spectral data.  (This is difficult, it requires both data that is not readily available to users and an engine that can deal with broader color spectra.)

 

Show some examples.

[Peter Milner]

Thanks Roy.

I tried the HDR option, but that gives me an image with huge lighting contrast which is difficult to deal with.

Messing with the histogram doesn't work as the extra information just isn't there and the graph breaks up.

I'll get our designer to look at option 3.

[Roy Hirshkowitz]

The extra information is probably there in our image editor, just a question of getting it to map a little broader in RGB space.  There are a pile of HDR editors out there other than PhotoShop.  Here's a sample.  Many of these have tone mapping choices we don't offer.

 

Option 2 would work better if you had some sort of control over the black end of the spectrum in our Image Editor.  (Something comparable to Burn for that end.)  I'm not sure how to do this.

[Peter Milner]

We've tried the equalize thingy, but it just sets all the levels at an equal low.

The next thought is, it may be my materials as a lot of them use bitmaps in jpg format.

I shall do a test using tiffs.

[Peter Milner]

I've tested this theory and the images I use for textures have full colour depth (maxing out on the graph), but when rendered, the depth is drastically reduced.

[Peter Milner]

Here's some screen shots supplied by our graphic designer which show what is going on.

The above render uses a very high quality tiff image for the wood veneer. Notice the levels on the right

This shows the material image used. Note that the colour depth peaks at maximum.

Here's a similar photo to the render. Again the levels reach maximum.

Here's some relevant information on histograms.

[Roy Hirshkowitz]

Ah-- I think I'm understanding a bit better now.  This is probably more of a color saturation issue....

 

Quite a bit of neutral (gray scale) is being added by the specular (glossy) component of the material.  Just for experimentation, try setting the highlight intensity to 0.0 for your wood materials and re-rendering.  See if the saturation is closer to what you're looking for. Obviously the overall material won't be acceptable-- just trying to narrow the issue a little.

[Peter Milner]

Okay. I removed all the reflective properties from most of the materials. As you can see it hasn't solved the problem.

Notice also the spikiness of the graph rather than the smooth transitions of the photo.

[Roy Hirshkowitz]

Is the color closer to what you want?

*****

The only fair way to do this comparison is going to be to render exactly the same scene and the photo. You also might want to take the photo at different exposures.  There are many, many variables here, so I'm not sure it's worth it.  Might be interesting.  Photography will likely always be better, at least with the current state of the art.

*****

Just in case the problem is one of saturation-- you should know that this is very common.  The picture you use for a wood texture already incorporates the glossy component, while when rendering it's only used for the diffuse reflectivity.  Most CGI professionals adjust for this by oversaturating the texture a little.

*****

Is your graphic artist is requesting more than 8-bits per channel?  That's a different issue.

 

 

 

 

 

 

 

[Peter Milner]

I don't think it's a saturation problem.

It's more as if the rendering only uses a limited pallet of colours.

So as you edit the image in Photoshop (colours and exposure) gaps start to appear in the histogram and the image starts to exhibit noise.

It's as though the rendering doesn't have the breadth of colour as a photograph.

[Roy Hirshkowitz]

None of the input colors are clamped in any way.  In fact, all calculations are in floating point which has even more accuracy than the standard way of using colors as three 8-bit channels.

 

What you're describing is still closest to saturation from a technical standpoint (as far as I can tell) -- a phenomenon which could easily be described as "breadth of color" by a layperson.  This term doesn't really have a technical analog.

 

Both tone-mapping and glossiness can affect this stuff and cause the rendering to look more neutral (gray or "washed-out") when compared to expectations.  Scott's run into this with wood textures in the past. I just spoke to him-- he's going to prepare a few examples.  He said he has seen it in textures where the channels have very distinct color spikes, with large areas of the per-channel histogram that are close to zero.  Your example above has that characteristic.

[Ros. Riha]

Recently, I used some of Arroway texture sets and I am not able to make nXt to produce images brilliant enough to be compared to their sample renderings - my results are always shade less crisp.