The unit is set to "mm" in the Crop tool but I want to crop in pixels. How do I change the measurement metric?
The crop unit is inherited from the selected (highlighted) process recipe in the Process Recipes tool located in the Output tool tab.
Most process recipes have the Scale field in the Basic tab. When you set the Scale field to Fixed, you will be able to select the unit in the Size field of the Crop tool.
In case you select any other option from the drop-down menu in the Scale field and set the measurement metric to in/mm/cm/px, the size unit in the Crop tool will inherit it. Thus, it will not be possible to change that.
In the process recipes with no Scale option, you will be able to set the desired unit in the Crop tool.
The information about the output image will be reflected in the Process Summary tool.