I think the process is like this: Make a mockup in Photoshop and then open HTML&CSS editor and write as much code as you can without using slice methods etc.
Some might approach it differently but I NEVER do mock-ups in any photo editing software. Ever. I think it is unhelpful at best. I will perhaps sketch something on paper… but that’s it. I literally open up a text editor and just start coding.
The biggest thing I don’t want to do is get my heart set on some design or design element that cannot be done reliably in the real world of code. Especially when it comes to responsive design. There’s certain things that just don’t really work.
I work all by myself though. If I worked on a team with a ‘real’ designer who makes mock-ups in Photoshop… then I’d have to learn that skill. For right now, I never do it that way.