The Color > Histogram effect

We have just seen that it is possible to work on pixels using curves.
TVPaint Animation also offers the possibility to work on the colors on a more «statistic level» thanks to the Histogram effect.

The first function of the histogram is to provide information about the distribution of colors on the screen.
Let's take for example the images below and select the Master tab in the first row of tabs and Luminosity in the second. We will obtain the following graphs :

The Log box enables use of a logarithmic scale instead of a proportional scale. For the moment, pay attention that this box is not checked …
* The more dark pixels the image on the screen contains, the more dense the graph is to the left (this is the case for our red planet).
* The more light pixels the image on the screen contains, the more the graph is concentrated on the right (this is the case for the image of the tree).
For a luminosity value given in the abscissa, the graph proportionally represents the quantity of pixels of the image having this luminosity value on the ordinates axis.
The blue curve represents the percentage of pixels having at least attained the luminosity value in the abscissa, the vertical red line represents the pixels the luminosity of which is the most represented on the screen.

The tabs Red, Green, Blue and Alpha work according to the same principle and image analysis is reduced to the channels of the corresponding colors.

The second function of the histogram, as you may have guessed already, is to modify the color properties of the image or video of the current layer (here again, the animation keys lock the parameters for a given position in the timeline).
To do this, we have to use the slider system of the histogram. You may use two, three or four of them. The latter enable re-calibration of the histogram by stretching or contracting it.
Let's again take a look at the pixel luminosity component. Below, you see the example of luminosity modification using the three sliders:

Before application of the FX stackSettingsAfter application of the FX stack

The section of the histogram between the abscissas 25 and 128 will be contracted to fit between the abscissas 0 and 51. The section of the histogram between 129 and 255 will be stretched to fit between abscissas 52 and 255.
This means that the dark components of the pixels in the image will be reinforced and contracted whereas the light components of the pixels in the image will be redistributed, spread and therefore reduced.

The tabs Red, Green, Blue and Alpha make the other graphs relative to the current image appear. Each of them may be modified independently of the others.

The principle of contracting and stretching is the same, regardless of how many sliders are used. Only the number of contracted or stretched intervals changes..

The first row of tabs contains four tabs: Master, Shadows, MidTones and HighLights.
* Clicking the Shadows tab limits the impact of the slider modifications to the dark colors, gradually.
* Clicking the MidTones tab limits the impact of the modifications to the medium tones and will reduce them progressively and finally cancel them out for the dark and light colors.
* Clicking the HighLights tab limits the effects of the histogram modifications to light tones, the latter waning progressively then canceling out for the medium and dark tones.
* The Master tab affects all color ranges in the same way.

Look at the following graphs for a better understanding:

Three curves are represented:
* The black curve represents the impact of the modifications in the histogram on the dark tones (Shadows tab)
* The gray curve represents the impact of the modifications on the medium tones (MidTones tab)
* The white curve represents the impact of the modifications on the light tones (HighLights tab)
The tones concerned are located on the abscissa.
The impact power is represented on the ordinates axis (the higher the curve for a given range, the higher the influence of the histogram modification on this range).

The circled sliders in the graph opposite are used to move, contract or stretch the three curves and, consequently, modify the effect of the tabs.