The Extraction tool is an easy way to gather structural textures from photos. All you have to do is to place the grid over the object of interest and have the perspective correction applied automatically.
Adjust the Size (Width x Height) of the resulting texture at the Output panel. You can automatically convert the extracted texture to a seamless one by increasing the Seam parameter. This works best on textures, that don't have a well-visible structure.
The interpolation, which takes place while applying the perspective correction, can lead to blurred images. You can compensate this with the Sharpen value.
Press the Render button at the bottom of the windows to export the extracted texture.
The Corner Brightness Correction can remove illumination gradients from the extracted texture by e.g darkening some of the corners. Very often, pressing the Calculate button already leads to useable results:
The Distortion Patch is the most important part of the Extraction module, because it defines the position and shape of the extracted area. Increase the Grid values to make more inner lines to be drawn. The Correction and Padding parameters are used to compensate distortions, which result from odd camera angles.
If you enable the Rotatable switch, the distortion patch will be rotatable and display a rotation control at its center.
While moving the grid or one of its corner points, press the SHIFT key to limit the movement to horizontal direction, and the CTRL key to constrain it vertically. Use the + and - keys to rotate the grid by ten degrees around its center.