If you check 'resample and the constrain boxes', the pixel dimensions in the top box, become active and you can change the dimensions in pixels.
In the 'document size' box, you cant force it to show pixels as it comes up with an error message.
Hope this helps.
Yes, this is what happened when I tried it
Richard
I've been wrong before!!Happy to have constructive criticism though.Gear used Canon 50D, 7D & 5DMkII plus expensive things hanging off their fronts and of course a "nifty fifty".