Colour separations for screen printing
Reduce artwork to a few flat ink colours and download one black-on-white film positive per screen, with registration marks, the hex list and optional trapping.
1Artwork
Drop your artwork here
PNG, JPG, WebP, GIF, AVIF or SVG. Transparent areas print nothing. Nothing is uploaded.
Sample: peacock plume half drop, 646 × 508 px.
3Inks
Working…
6 colours found. The lightest is left as the fabric, so 5 screens.
2Colours
Prints 2.15 × 1.69 in (5.47 × 4.3 cm).
From artwork to screens
Screen printing lays down one ink at a time, each through its own screen, and each screen is exposed through a film positive that is opaque where the ink should go. This tool makes those positives: one black-on-white PNG per colour.
- Number of colours: how many flat colours, fabric included, to reduce the artwork to. k-means looks for the colours that best represent all the pixels, measured in CIELAB, where distances follow perceived difference. Median cut keeps splitting the range of colours at the middle; it is quicker but can blend small accent colours into their neighbours.
- Merge near colours joins any two results closer than the ΔE you set. A ΔE of about 2.3 is the smallest difference most people notice, so values from 3 to 10 merge shades nobody would print separately.
- Fabric or paper colour leaves the lightest (or darkest) colour unprinted, as bare cloth.
- Clean up specks gives tiny islands of colour to the colour around them; they rarely hold on a screen.
- Trap spreads each lighter ink a few pixels under its darker neighbours, so a slight misregistration leaves no gap.
- White underbase adds a screen covering every inked area, shrunk (choked) so it does not peek out, for printing on dark fabric.
Example: the sample tile has an ivory ground and five inks. At 6 colours with the lightest as fabric you get five screens; at 300 DPI each film prints 2.15 × 1.69 in (5.47 × 4.3 cm) plus a 0.4 in margin for the marks. Use the print export first if the design needs to be larger.
Sources
- Wikipedia, Screen printing: one colour printed at a time with its own screen, exposed through film positives.
- Wikipedia, Trap (printing): spreads and chokes, and why the lighter colour is spread into the darker.
- Wikipedia, Color difference, citing Sharma, Digital Color Imaging Handbook (2003): ΔE*ab ≈ 2.3 as a just noticeable difference.
- Arthur & Vassilvitskii, k-means++: the advantages of careful seeding (SODA 2007), and Heckbert, Color image quantization for frame buffer display (SIGGRAPH 1982): the two reduction methods.
Questions
Why do I get colours I never used?
Smooth edges in a digital image are made of in-between pixels, so a design with five inks can contain hundreds of shades. If one of those edge shades gets its own colour, lower the number of colours, turn on Merge near colours, or clean up specks.
Which colour should be printed first?
The list runs from lightest to darkest, but the print order is your printer's call: it depends on the inks, the fabric and the press. The file names are numbered in the same light-to-dark order for reference.
Do the separations include halftones?
No. Every pixel is either ink or no ink, which suits flat spot-colour designs such as most repeat patterns. Gradients and photos turn into flat bands of colour; they need halftone separations made in dedicated prepress software.
Can I print the separations myself?
Yes. Print shown separation sends the current film to your printer at its real size for the DPI you set; choose 100% or actual size in the print dialogue, not fit to page. The PNG files also carry their DPI, so other programs print them at the same size.
Is my artwork uploaded?
No. The colour reduction runs in a background worker inside your browser, and the separations and ZIP file are built on your device.