How to Do Color Separations for Screen Printing in Photoshop

To separate a design for screen printing in Photoshop, you build one channel per ink. Select each color with Select > Color Range, save the selection as a channel, set it up as a spot channel in the ink's color, add a white underbase if the shirt is dark, halftone any channel that carries tone, then print each channel to film with registration marks.

This guide walks through that spot color workflow step by step, with the settings screen printers commonly use, and ends with a faster route for days when there is no time to do it by hand.

Set up the file before you separate

Separation is much easier on a clean file. A few minutes here saves an hour of fixing channels later.

• Work at final print size. Set the canvas to the size the print will be on the garment, in inches or centimeters, before you start. Resizing after you halftone ruins the dots.
• Keep enough resolution. Ryonet's guide to halftones in Photoshop recommends 600 DPI as the output resolution when you convert a channel to a Bitmap halftone.
• Flatten a working copy. Keep your layered original, and separate from a flattened RGB duplicate.
• Clean up stray colors. Soft, anti-aliased edges and JPEG noise create in-between colors that Color Range will half-select. A light cleanup, or reducing the art to its real ink colors first, gives crisper channels.

Then decide your ink list. Write down every ink you plan to print and the shirt color. Each ink is one screen, so this list is also your quote.

Step 1: Pull each color into its own channel

Work through the inks one at a time.

1. Open the Channels panel (Window > Channels).
2. Choose Select > Color Range and click the color you want with the eyedropper. Raise or lower Fuzziness until the preview covers that ink and nothing else. Shift-click to add a second shade of the same ink.
3. Click OK, then click the Save Selection as Channel button at the bottom of the Channels panel. A new alpha channel appears.
4. Deselect and repeat for the next ink.

In each channel, black means ink and white means no ink. Gray means a partial amount, which only prints if you later turn that gray into halftone dots. Check each channel on its own by clicking its eye icon, and paint out anything that does not belong.

A practical tip from experienced separators: arrange the channels from light to dark, in the order you plan to print, and keep a channel showing the garment color at the top so your preview matches the shirt.

Step 2: Turn the channels into spot channels

Alpha channels are just masks. To preview the separation in real ink colors, use spot channels.

1. From the Channels panel menu, choose New Spot Channel.
2. Click the color box and pick the ink color. You can choose from a color library if your printer works from a named ink system.
3. Set Solidity. This only changes how opaque the ink looks on screen. It has no effect on the printed separations, so 100% suits opaque plastisol and a lower value suits transparent inks.
4. Load your saved selection for that ink and fill it in the spot channel, or paste the alpha channel's contents into it.

Name every channel after its ink and its print order, for example "02 Red" or "03 Black". The person burning screens reads those names.

Step 3: Build an underbase for dark garments

Inks on a black or navy shirt look dull without a white layer underneath. The underbase is its own screen, printed first and usually flashed before the colors go on top.

A common approach is to combine the selections of every color that needs brightness, fill that combined area in a new channel, then adjust it with Curves so it is solid where colors must be bright and lighter where the shirt color should show through. Some separators mask the art on a black background, convert a copy to grayscale and invert it, then apply a strong curve to get the same result.

Then choke the underbase: shrink it slightly so it sits just inside the top colors. If it is the same size, white peeks out at the edges whenever the press drifts. ScreenPrinting.com's white base guide does it by loading the underbase channel as a selection, choosing Select > Modify > Contract with about 1 pixel at 300 DPI, then Select > Inverse and Delete to trim the edge. The opposite move, spreading a color so it overlaps its neighbor, is covered in our guide to trapping, choke and spread.

Step 4: Halftone the channels that carry tone

A screen can only print ink or no ink. Any channel with gradients, soft shadows or partial coverage needs to be converted to halftone dots, or the gray areas will either fill in solid or wash out.

The manual route is to copy the channel into a new grayscale document, then choose Image > Mode > Bitmap and select Halftone Screen as the method. Photoshop then asks for frequency, angle and shape. For the reasoning behind each value, see our deep dive on halftones for screen printing.

The mesh rule comes from ScreenPrinting.com's screen mesh guidance, which suggests a mesh count four to five times your line frequency. Agree the LPI with whoever prints the job, because many shops prefer to output solid channels and let their RIP software apply the halftone at their own settings.

Step 5: Add registration marks and output film

Every film needs identical registration marks in the same position, outside the print area, so the printer can line up each screen.

• Photoshop's print settings include registration marks, corner and center crop marks, a negative option and a flip option, which covers most film needs.
• Many shops instead draw a small crosshair target in the margin of every channel, so the marks travel with the file wherever it is printed.
• Print each channel as its own film positive: solid black where ink goes, clear everywhere else. A dedicated RIP such as AccuRIP, which prints from Adobe apps to supported inkjet printers, gives denser blacks and more consistent dots than a standard print driver.

Before you burn anything, print a composite proof at 100% and lay each film over it on a light table. Misaligned marks or a missing ink are far cheaper to find here than on press.

Mistakes that show up on press

• Gray in a spot channel: soft edges that were never halftoned print as ragged, half-filled outlines.
• No choke on the underbase: a white halo around every color.
• Resizing after halftoning: broken, uneven dots and moiré.
• Too many screens: two nearly identical colors that could have shared one ink. Merge them before output.
• Unlabeled films: the press operator has to guess print order.

The faster route when the deadline is today

Manual separation in Photoshop gives you total control, and it is still the right call for complex photographic work. For flat spot-color art, the selection and channel steps above are mostly repetitive, which is where automatic tools help.

Texloom's Separation Studio separates a raster image or PSD into spot-color plates automatically, or into exactly the number of screens you choose, from 2 to 12. It can add 0 to 4 px of trapping, registration marks on every plate and a white underbase for dark garments, and it names each plate after its nearest color in the Texloom Color Library. Export a layered PSD and you get each plate as its own layer, ready to check and finish in Photoshop with the halftone and output steps above.

If you separate photographic art every week, a dedicated plugin may be worth it. Our comparison of the best color separation software for screen printing covers T-Seps, UltraSeps, Sep Studio NXT and the free options.

Next step: take a 3 or 4 color design, separate it by hand once using the steps above, then run the same file through Separation Studio and compare the channels side by side. You will quickly see which jobs are worth doing manually.