Tuning Sketchfab Post-Processing

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Hello! I’m Shaderbytes and today I would like to share some knowledge on the art of fine tuning post processing filters on Sketchfab. This information is also useful to any other art medium as well.

Let’s begin with looking at what I will be talking about today:

  • Identifying the problem.
  • Introducing a balance plan.
  • Examples of how to apply balance

Identifying the Problem

When thinking about balance in regards to post process filters the two most problematic areas would be an overuse of filters or using too strong values for the filter properties. This is a common mistake novice digital artists tend to make even in 2d art design using a graphic editor like photoshop. Although it must be said that even experienced artists can fall into the trap of over filtering their work from time to time. This happens to me as well but I do tend to eventually fix it based on knowing to look out for this kind of overuse in my artwork.

The two examples above show balanced artworks on the left and unbalanced on the right. The unbalanced versions suffer from both problem areas I mentioned: Too many filters applied and also too strong settings.

Introducing a Balance Plan

Firstly let us tackle the easy part of balance which is simply to use less filters. Just because the option is there does not mean you should use it. I do not need to discuss each filter here but I will mention some which you should consider not adding unless the artwork meets certain conditions.

Chromatic Aberration

Chromatic aberration is a filter I almost never use at all. Truth be told chromatic aberration is an undesired effect caused by the lens of real world image capturing equipment. Most photographers would actually try and remove this from their images in post production. So why does this filter exist in CG? The problem in CG is that rendering is too perfect. This filter can then be used to add imperfection to the render. This can be useful but does not suit all types of CG art styles. I personally would only think of using it on CG artwork that is aiming for photorealism. So in the sample picture I posted above of a low poly toon styled scene this filter would not be used.

Bloom

Bloom is a fantastic filter but also has specific usage. Your scene would ideally need to have some strong lighting and materials that have highly reflective properties. Also for materials that are emissive like lightbulbs or car headlights etc. I use this filter often in my art work but again looking at the sample scene I posted above you will see that there are no highly reflective or emissive materials so there would be no point in using the bloom filter here.

Grain

This filter falls into the same category as chromatic aberration, I would personally only think of using it on scenes where the art style is aiming for photorealism.. Or otherwise it really needs to be a subtle background effect, except in certain edge case scenarios where the artwork is simulating low light noise.

Depth of Field

I often see this filter used on scenes that have only one object in the scene like a character or a car and it is quite annoying. In general using this filter on a scene that does not have very much depth from a geometrical point of view should be avoided. I say in general because this is not a hard fast rule. It is useful to simulate a macro photography type scene. Either way you should honestly question yourself each time you think of using this filter whether it is really needed or is the look you were aiming for because this is definitely one where you can fall into the trap of adding it just because it it there.

Examples of How to Apply Balance

So after consideration of only using filters that will actually enhance your artwork in a meaningful manner based on the art style, let me introduce a method of balancing the properties of the filters you are planning to use.

Version Comparison

The trick I use here is taking screenshots along the way. It is very difficult to keep a mental image of one version of your settings to another and you can end up going in circles. Comparison images are your best tool to find balance. Remember I mentioned that the common trap is settings that are too high. So I start out by making the first version of settings according to how I feel it looks good. From there , knowing the pitfalls, I work at reducing settings and taking another screenshot. I might repeat this process several times fine tuning the properties up and down, comparing the versions until a correct balance is achieved. Here is an exposure comparison.

Categorise Filter Strength

The strength to which some filters are applied can be thought of as layering or blending. You can divide the concept of blending into three categories : foreground , middle and background, or strong, average and weak etc. When adding certain filters it is helpful to decide which category of blending this filter falls into. Foreground means it is very obvious and strong. Middle means it is there playing a part but does not really stand out. Background means it is extremely subtle , you would really have to look for it to see it.

Grain is a perfect example for this. Ideally you want it to be contributing to the image but in a subtle manner. If you look for it you will see it, but otherwise when just looking at the render in general it does not stand out. So this is middle or background. There would be edge case scenarios where you are working on some stylized art, like perhaps a scene which needs to look like it is viewed through a night vision device or something similar. In this case you would want the grain to simulate low light noise and it would be a foreground effect.

The pitfall to look out for here is that all your filters should not be set as a foreground effect. SSAO and Sharpness filters are probably also best used in a middle to background role.

Tone Mapping

I want to make special mention of this filter because to me it is probably the most important filter to use in tweaking your render and I use it in most of my own work. Generally speaking it is used in nearly all modern real time rendering engines. It is also a candidate for abuse and so some consideration should be applied here.

Firstly let me point ot that tone mapping is not a substitute for good lighting and material settings. If you find that you have all the properties of the tone mapping filter cranked up high then it is a good sign of not having the correct settings in your lighting and materials. Except for exposure , I find tweaking the environment map exposure or simply using the tone mapping exposure have similar results.

A common mistake is to think everything looks better with higher contrast and higher saturation. Try to avoid this mindset. Of course these properties are useful, but if you are always setting both of these very high in all your artwork then something is not right, especially in conjunction with the filmic algorithm.

Here are three examples to prove this point: where saturation is reduced, contrast was increased only in the first example, in the other two notice it is drastically reduced. Linear and Reinhard algorithms were used.

I do use filmic as well but I would suggest to never increase the contrast in combination with this algorithm since it produces pretty strong clipping to the levels already. Here is an example using Filmic :

Conclusion

The Sketchfab post processing stack is a marvelous tool and can really enhance a 3d scene from great to fantastic! Along the way just keep it in mind that this same tool , when overused can in fact work in the opposite fashion. Keep striving to find the balance.

About the author

Ian Pretorius

Ian Pretorius

Digital Media Developer residing in Sunny South Africa. I'm passionate about digital art especially in regards to real time rendering.


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