halftone screen help

here are my instructions for a photo... i acted like i knew what my boss was talking about bc i didnt want to look like an idiot. but honestly i forgot what this stuff means.

-convert to halftone
-screen halftone to 20%
-120 lines

I have to prepare it for film too, in case that changes anything.

Thanks in advance for any help

[QUOTE=carriem26]here are my instructions for a photo... i acted like i knew what my boss was talking about bc i didnt want to look like an idiot. but honestly i forgot what this stuff means.

-convert to halftone
-screen halftone to 20%
-120 lines

I have to prepare it for film too, in case that changes anything.

Thanks in advance for any help [/QUOTE]

My understanding would be:

"convert to halftone" I would assume grayscale halftone IMAGE>MODE>GRAYSCALE

"Screen haltone to 20%" I'm guessing you are suppose to "ghost" the image. CTR+M (CMD+M on mac) to bring up the curves dialog box and set "OUTPUT" to 20%

120 Lines would be lines per inch talking about the linescreen used to print the image. Linescreen is Resolution dependent and as a general rule you want twice the resolution as the linescreen 120 x 2 = 240 DPI. The bare minimum resolution can be calculated "Linescreen x 1.414 = Minimum resolution"