Blur your Traces in Blender

Gernan Version

The last time I have explained how to hide compression artifacts using the Bilateral Blur.
But there are many other situations which lead to nodes destroying your picture.

Here for example:

We see that a simple Hue Correct node may give us hell quite often!
Although our initial impression implies that those borders did also arise from compression artifacts, the real core of the problem hides in the hue channel because especially in image areas with low saturation and high brightness the hue values may change abruptly from pixel to pixel so that problems occur.
That is one of many situations which raise the desire to have a feathering feature, providing the ability to blur the effect a node applies to an image, but not the image itself, in every node
Unfortunately the most nodes don´t provide such a setting, but we may use a technique that turns out to be useful in many situations.

The Idea is to extract the change a node has applied to the image, do something with and then reapply it.

This simple setup does exactly that:

Edit: Oh, of course the Inputs of the subtract node have to be swapped opposed to the image!

We subtract the original image from the output of our node and so get the difference. That is exactly the change the node has applied and we may do with it whatever we intend -  in this case we apply a blur and readd it to the original picture.

The artifacts have gone!
Imperfections like this do often occur around fine structures like trees in front of blue sky.
But the concept of extracting a node´s effect is incredibly useful in many more situations and you will quickly see yourself use that technique quite often.

That´s it for today.
The next time I will show you some interesting ways to misuse RGB Curves, so stay tuned!
In addition I am considering to write a complete how-to about my workflow for editing Videos in Blender, including explanation for the many useful addons out there. Please leave a comment if you´d like to read about that!