From Meshlab

The editing Quality Mapping Tool is a tool for the fine tuning of how scalar values, defined over a mesh, are mapped into colors.

Note that this filter will not work if quality values are not defined over the mesh vertexes.

Contents 1 Main features 1.1 Transfer Function 1.2 Equalizer 2 Tutorials 2.1 Stressing the curvature of a mesh 2.2 Giving a tone to a mesh 2.3 Applying the same mapping to several meshes

Main features

The tool is composed by two main section:

Transfer Function

The Transfer Function maps, through a linear chart, the distribution of the values of RGB channels over a linear space, identified by a color band. The transfer function view is interactive, in fact the user can modify the distribution of the channels values using handles, that can be added, moved or removed. To add a new handle to the Transfer function, it's necessary first to select the channel for the handle (by selecting the forward channel in the top-right radio button group, or by clicking on an handle of the same channel), and then double-clicking in an empty place of the transfer function view. It's possible to remove an existing handle by double-clicking over it. Every time a change is performed to the transfer function, it's immediately visible in the color band below. More over, it's possible to save the current transfer function in a CSV file or load it. Important Note: When a transfer function is loaded from an external file the changes to the current transfer function will be lost.

Equalizer

It represents, through an histogram chart, the distribution of the quality over the mesh (x-axis represents quality levels, y-axis represents the number of vertexes with a certain quality). Like the transfer function view, the histogram one too is provided of handles, exactly three. Each handle has a different meaning: the leftmost one, represents the minimum quality limit, the rightmost one the maximum quality limit, and the middle one represents the position of the middle quality level respect to the minimum and the maximum actual values. The portion of histogram delimited by lateral handles is mapped in the transfer function (visible as background of the TF view). So, all the quality levels included in the range between the histogram beginning and the left handle position will be mapped with the leftmost color of the color band, while the ones between the right handle and the histogram end will be mapped with the rightmost color. All the other values of the histogram are mapped in the color band depending by the relative position of the middle quality value. This value is the parameter of the exponential (or logaritmic) function used to interpolate the TF nodes when mapping quality levels on color band. The curve representing this function is viewed in the gamma correction panel. If a lateral handle is moved outside the histogram, or if the user sets in a "lateral" spin box a quality value greater than max or lesser the min, the histogram will auto stretch itself. Finally a slider can be used to change the brightness of the color band colors.

Tutorials

Stressing the curvature of a mesh

1. Apply the filter Colorize/Gaussian Curvature (equalized)
2. Open the Quality Mapping Tool
3. Choose the RGB color preset
4. Quality values over Gamma Curvature are often concentrated in a tight range between -a and +b. So manually set middle quality to 0. Try setting minimum and maximum equalizer values to stretch the significant part of the histogram all over the color band, so that negative values will be colored in red and positive ones will be colored in blue, while quality values around 0 will be colored in green
5. You can even modify the transfer function to eliminate the green color and extend red and blue to all the color band

Giving a tone to a mesh

1. Apply the filter Colorize/Ambient Occlusion
2. Open the Quality Mapping Tool
3. Choose a color preset (i.e. Red Scale)
4. Modify the transfer function to obtain the color scale you like
5. Set the minimum/middle/maximum quality value in equalizer to adjust the tone depending on the distribution of quality over the model

Applying the same mapping to several meshes

1. Set the Quality Mapping tool with significant values
2. Save preset to a file (it will contain transfer function and equalizer parameters) and close the tool
3. Open a new mesh
4. Open Quality Mapping tool
5. Click on load preset,locate the CSV file you previously saved and apply the filter.

Alternatively open the filter Quality Mapper Applier, locate CSV file and apply the filter. This filter can be used also in Meshlab command line. Note: all the files should have similar quality values to be colored in a significant way(i.e. applying the same colorize filter)