Initial study of the FX stack

Load the Palette project. Spread the layer over thirty images.

We obtain the following timeline and screen:

Our effect stack is presently empty.
Select the effect Stylize > Mosaic from the menu. The effect stack must look like the one shown opposite.
Now modify the parameters Width and Height by setting the values to 20 and 30.

The result is immediately visible on the current image: the image is cut in blocks of 20 pixels in width and 30 pixels in height (the color of a block is equal to the average of the pixels making up the block in the original image).
The Smooth button enables blending between adjacent blocks, the image obtained is therefore closer to the original image.

Original imageImage with preview of the effect

That said, the right image above is, in fact, for the moment only the preview of our mosaic effect (disabling the Preview button allows you to return to the original image).

To validate your settings and apply them into the current layer, all you have to do is apply your effect : click on the Apply FX stack button at the bottom of the FX stack window. Your current layer will be modified according to your settings (if required, use the Undo option to undo the modification…). Don't forget that all images of the layer must be selected if required.