Node editor: HSL color [Blender]

The colormodel best known is the RGB; uses three channels of information to the primary color components (Red, green and blue) and, sometimes, Additional other known “alpha” which is used for information about the transparency of each pixel. There are other models such as the HSL representing colors with another coding approach.

Terms and technical data on the color encoding parameters can be found in “Color Appearance Modelling for Color Management Systems” CIECAM02.

HSL comes from the English HEU, Saturation, Lightness which indicates that stores components “Tonality”, “Saturation of color” and “luminance” for coding the colors.

?What are these color components?

To answer this question we will have a series of examples with the Blender node editor. We do not want to deepen the mathematical aspects HSL model, rather will approach the problem from the point of view of the practical use of filters incorporating the Blender node editor for retouching images, and animated in post-production. HSL will apply a filter to an image and its parameters vary them getting different results illustrative.

The image you use must have the basic colors to appreciate the effect of the filter to apply: filtro HSL; We'll see the result using a viewfinder connected to the output of the filter. The scheme of node editor we need may be similar to the following:

Image “rgb00001.jpg” is used as an input to the node “Hue Saturation Value” which processes, producing a new image we use as an input to the viewfinder “Viewer” or output ficero (not shown).

The latter means that, besides the visor, We can also add an output node (output) to a file (File) to save the images of the tests we perform.

Even add the filter editor menu select:

Add->Color->Hue Saturation Value

The first case study I will make with the values ​​seen in the image of the filter. With these values ​​we obtain the result by applying the filter is very simple, it will output the same image that we find used as input.

As shown in the image, values ​​are located between the smallest and largest of those available in each range, right in the mean value of the controls available on graphic interface.

So, we use 0,5 for pitch (Hue). The range values ​​range between 0 and 1.

Similarly, saturation the leave in “1” because the range varies from 0 to 2 As the luminance value (Val).

• H: Hue: Shade from 0 to 1
• S: Saturation: Saturation from 0 to 2
• L: Lighness: Luminance from 0 to 2

Tonality

The tonality affect or determine the color. It will “move” Input color scale using as reference cyclic.

If we change only the value of the key, see that the maximum and minimum values ​​are equal. Values ​​are defined circular, as a “color wheel”. The result is a change only the color of objects and background.

In the next sequence we see how this parameter affects HSL filter to the image that we have used as input to the same. The change was made starting from the minimum value (zero), uniformly increasing until the maximum (one), namely, 0, 0.1, 0.2, 0.3 …..

Saturation

Another parameter in the filter HSL color saturation is. We can get from a black and white image, to one in which the colors are a high intensity (color saturation). The sequence can see the variation of the saturation of the image prior to vary again the corresponding parameter between its minimum and maximum values.

Luminance

Similarly to what was done in the previous cases, keep the values ​​of Hue and Sat and vary the third parameter.

Determines luminance “density” luminous flux of an object. Normally discuss “intensity” light to describe this aspect. A zero luminance will give us a completely black image, while higher values ​​we produce an effect of “Overexposure” or “burned” picture.

HSL filter application

An example of more complex application, in which we use the HSL filter to image black and white image that will be used as input to a filter contour recognition (figure obtained with a Sobel filter). The resulting image the mix (MIX) the original to reinforce the edges of the elements, as in an image “ghost”.

First scale the image to the desired size. Filter “Scale” perform this function. We will indicate the scaling factor.

Then we will remove the component saturation of color of the image with the filter HSL (use a null value for the parameter Sat)

The Sobel filter enable the recognition of the shape of the elements of the picture

Mix the two images (node MIX) and we obtain the final result

Without the filter, HSL, applying only the filter “Sobel” contours would obtain color components, simulating the effect of “neon lights”

and the mixture would give an image similar to the following

HSL color model (Wikipedia)

Blender Tutorial