THere are some filters and plug inn's out there that convert images to halftones. If you haven't found them or they aren't working as needed, Here's a manual method. This will be true to your actual seps. Solids are a solid. 5% on yellow screen has a 5% dot on yellow area.
This is only If you happen to be doing your seps in Photoshop, you can do it manually.
If starting from a vector file, you CAN also, copy and paste a black and white with grayscale tones from vector (into photoshop) and get the same thing. Very similar or identical, + a few steps (to converting your seps to halftone for use on films... using the bitmap mode.
WHAT WE WILL DO:
In photoshop, once converted to halftone, you will reengineer the individual colors (back into rgb layer channels using the halftoned spot color channels for that sep. I also turn down the opacity on an underbase to about 65-75% for sim process and assign the top colors 100% or something equivalent to your inks opacity (and the size mesh you are using). A 110 mesh may be 100% opacity in the RGB layers while a 305 will be in the 30-40% opacity range for sim process. It's close to what you get on press with the halftones built in but don't count on it being 100% accurate.
If you're not familiar with creating your own halftones in photoshop, (people use that when they don't have a RIP yet). Here are the steps.
PREPARATION:
1, If you have an RGB or CMYK with multi channel sep, you need to first (delete) the RGB or CMYK. Then, whats left are the channel seps. you then need to SPIT channels (In channels window, go to the top right side and find the little black arrow head. Click and hold, drag down to PLIT CHANNELS. This breaks them up into individual grayscale files. (skip this part if you are only trying to show or use halftones on a background color of a single color grayscale file image).
You must first have grayscale files in order to convert to a single bitmap image. (NOTE: pixel size and cleanliness of the dots are based on file resolution. A 72 ppi file provides poorly shaped dots. They are very large, visible and produce blocky circles or curved shapes. A 300 rez file provides cleaner dots and a 600 ppi file provides usable dots (on film). You can go higher, such as 1200ppi for great dots = to many desk top films printer resolutions... but for jpg presentations, a 200-300ppi file is all that is needed.
For actual output of the dots, (using them for seps), I suggest at least 600ppi at a minimum. The pixels are either black or white in bitmap mode. To produce smaller or larger halftone dots means that more of the actual size pixels are used forming your % dot. Once you have your individual grayscale files, do the following.
HALFTONE PROCEDURE:
1 From a grayscale image, go to IMAGE, MODE BITMAP.
2 Punch in the desired resolution for your needs. (Presentation or final output quality).
3 Under METHOD, Chose HALFTONE.
4 Enter the line screen, angle and dot shape you will typically use on press.
5 SAVE AS a copy... name color and print sequence.
6 Close out that working file...and do not save changes.
7 Go to the next color and repeat.
MERGING FOR COLOR PRESENTATION INCLUDING DOTS:
1, Open with photoshop, one of the sep files that you converted to halftone.
2, Select all, COPY and create a new file. A window ill pop up asking you to enter the specifics of that new file. This (copy) will give you the same resolution and file dimensions. You want to CHANGE the COLOR MODE to RGB.
The background can be white at this point, but once opened, Fill the background with the shirt color needed.
3, The next (important step) is to convert your seps (each one) back to a Grayscale mode. SIZE RATIOA will be 1.
RGB, CMYK and Grayscale work with tints and tones. Bitmap again, is a single pixel that is either black or white...and is spaced farther apart to indicate tone. For this reason, working in RGB, you must convert back to grayscale in order to work with that halftones sep in RGB mode.
4,Move each file window appropriately so that so can see and activate each one as needed.
5, Activate the channels window, and do not have the RGB layers in the background activated. This is so that your next step will be directed there (in channels) and not in RGB. If not, it will put your sep into the RGB layers and you do not want that yet.
6, While holding down on the SHIFT key, click on the SEP channel and drag that sep file to the channels window in your new RGB file.
7, From here, you select all black pixels in that channel by holding down the (control or command key). (This is not the same as selecting all). The act of holding down the key while selecting tells photoshop you only want to select actual pixels in that channel...and not the entire area.
8, Here is what you're looking for. With the selection still active, go back to the RGB layers, create a new layer, name is the color you are filling it with...and then in your color picker, select the color it's to be such as pms 185 red. Then fill that selection with the color. There is your sep color (in color) in rgb layers on your background shirt color.
9 Repeat for as many colors as you have in the file.
From here, you can save this layered (sep version) to play with later...but save a COPY at a lower resolution (for presentation). It will have your dots, and represent what it might look like on press a little more accurately. You can even reduce that and drop it on a tee shirt template in photoshop much the same way you do for rgb color composites.
It seems like a lot of steps, but after you do it a few times and know exactly where you're headed, you can get this down to about a 3 min step. YOu can also create an action to speed things up. I'm sure people are starting to sell actions like this, I just haven't seen this specific one yet I don't think. Once you get the steps down, you can create your own action. You just need to remember in your action, where you are puling your seps from to keep it on track.
