I have never used Photoshop for web page design, but am interested in seeing how Parfait works.
When I fired up Photoshop CC 2014 to create a layout, I was surprised that the web presets use a resolution of 72 pixels per inch. The CSS specification states quite clearly that a pixel is equivalent to 1/96th of an inch (I'm linking to the CSS 3 Candidate Recommendation, but the CSS 2.1 specification says the same).
How does Parfait calculate pixel dimensions? Is it based on the incorrect resolution used by the Photoshop presets, or can I safely change the resolution in a PSD to 96px to an inch?
With a little experimentation and the help of an Adobe engineer, I've found the answer.
If you accept the 72px/in web preset in Photoshop, Parfait treats points as pixels. So, Parfait reports a 60pt heading in the PSD as being 60px. However, if you change the Photoshop resolution to 96px/in, the 60pt heading is reported as 80px.
The problem with changing the Photoshop resolution from 72px/in to 96px/in is that Photoshop scales up images. So, a 300px wide image is displayed as being 400px wide.
The simple solution, for the time being at least, seems to be to accept Photoshop's incorrect understanding of the CSS definition of the difference between points and pixels.