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Guided workflow variation

Gradients and soft shadows,printed with a handful of inks.

A JPEG logo with a glow or a sunset fade will not split into tidy flat colors. Underbase index mode fits a small ink palette to the picture and dithers each pixel between those inks, so shading reaches the shirt as a fine pattern of solid ink.

Open the shaded file, let index mode fit the inks, set the dither strength and ink count, check the output dots, then generate the film.

Pay once. Own it forever.

One-time purchase on the Microsoft Store · No subscription · Instant install

Get it from Microsoft

Buy through the Microsoft Store—instant install, automatic updates, and a Microsoft receipt for easy expensing. No account needed on our site, and no subscription on Store purchases.

Full Underbase overview
One-time purchase No telemetry Local-first

windows · runs on your pc · no account · nothing uploads · 15-day free trial

If this sounds like your week

Shaded customer files do not break into flat plates.

Plenty of orders arrive as compressed JPEGs: a mascot with airbrushed highlights, a photo-style sunset behind a palm, a logo with a drop shadow. Splitting those by exact color produces hundreds of near-identical tones, each one a candidate plate, while blocky compression noise scatters stray pixels across the image. Forcing them into a few flat inks by posterizing turns smooth ramps into hard stripes.

Where tooling usually breaks

Banding and stray pixels show up on the shirt.

Posterized ramps print as visible steps. Noise leaves specks that clog fine mesh or vanish under the squeegee. Adding more colors to hide the steps pushes the job past the number of heads the press has, and every extra head means another frame to coat, expose, wash out, register, and reclaim afterward.

Where Underbase lands

Let the dither carry the shading.

When Underbase spots continuous tone, it opens the file in Index (dither soft edges and gradients) and says so in a notice. Each pixel is assigned to the closest ink with error diffusion. Dither strength runs from 0, which posterizes, to 100, which fully dithers; 70 is the default. Reduce to re-fits the palette to fewer inks, and Output dots shows every plate at film resolution.

Pay once. Own it forever.

One-time purchase on the Microsoft Store · No subscription · Instant install

Get it from Microsoft

Buy through the Microsoft Store—instant install, automatic updates, and a Microsoft receipt for easy expensing. No account needed on our site, and no subscription on Store purchases.

Learn more about Underbase

windows · runs on your pc · no account · nothing uploads · 15-day free trial

What you get

Feature highlights

Spot or index separation from the files customers send

PNG, TIFF, JPEG, BMP, GIF, WebP, SVG, PDF, and Illustrator (.ai) files, with close shades grouped, the background left unprinted, and shaded art dithered between a fitted set of inks.

A choked white underbase

built from the inks you tick, pulled in from 0 to 3 mm in 0.05 mm steps, with dark inks printing straight on the shirt and a preview on seven garment colors.

Trapping in one click

spread or choke any ink from -3 to +3 mm, or apply the default trap to every ink so lighter colors tuck under the darkest.

Halftones tuned to your press

screen any plate at your ruling, angle, and tint, take a ruling suggested from the mesh, thin halftones for measured dot gain, and check the output dots before film.

A plate budget you can see

Underbase counts the underbase and every printing ink against the screens your press holds, holds generation until the job fits, and merges inks to fit in one click.

True-size film and a production ticket

a film PDF with identical registration marks and plate labels, one plate per sheet or ganged, 1-bit TIFFs at up to 1440 dpi, and a ticket as PDF and JSON.

Especially when

  • Turn a customer PNG, JPEG, SVG, PDF, or Illustrator file into one plate per ink without selecting colors by hand in a design program
  • Build a white underbase for dark shirts that is choked so it never shows at the edges, and keep dark inks off it
  • Know the plate count before burning a screen, and merge inks to fit the screens the press holds
  • Print film positives at true size with registration marks and plate labels, plus a production ticket, without sending the job to an outside separator

Who benefits

Real-world scenarios

A sunset tee from a shaded JPEG

The customer sent a 9 x 9 in JPEG of a palm tree against a sunset gradient, with soft banding from compression and a dark title under the scene.

Underbase opens it in index mode with five inks, sets the white background to not print, and leaves black off the underbase. The budget tile reads 6 of 6 plates, and the Composite tab shows the gradient dithered between maroon, navy, purple, orange, and black.

Fitting shaded art to a four-screen press

A small shop runs a four-head press, but the shaded logo opened with five inks plus the underbase, which is two screens more than the press holds.

The operator sets Reduce to 3 and chooses Reduce. In index mode the palette is re-fitted to the artwork rather than merged, so the three remaining inks are fitted to the colors of the image, and the budget shows 4 plates.

A logo with a soft drop shadow

Most of the logo is flat color, but a soft shadow under the lettering fades into the shirt, and a hard posterized edge would look cheap.

In index mode, the operator lowers Dither strength until the flat areas print clean and only the shadow fades. Output dots in the Plate tab shows the dither at the output resolution, so the result is checked before the film is printed.

Deep dive

How index mode turns shading into printable plates

When Underbase picks index mode. When you open artwork, Underbase looks at how its colors are spread. Flat art opens in Spot (flat colours). Art with shading, gradients, or heavy compression noise raises a notice that it looks like continuous-tone artwork and opens in Index (dither soft edges and gradients), with a second notice naming how many inks it fitted. You can switch modes at any time in the Separation list.

How the dither works. In index mode every pixel is assigned to exactly one ink: the closest one in color. The difference between the pixel and the ink it got is carried to the neighboring pixels, a technique called error diffusion. Across a gradient, the share of each ink rises and falls with the tone, so a ramp from orange to maroon prints as a mix of orange and maroon pixels whose balance shifts across the area.

Dither strength. The Dither strength field runs from 0 to 100 in steps of 10, with 70 as the default. At 0 the image is posterized into hard regions of each ink. At 100 soft edges and gradients are fully dithered. Values in between keep flat areas clean while still blending the transitions.

Choosing the inks. Index mode fits a small set of inks to the image. Reduce to sets the target from 1 to 16 inks; in index mode, Reduce re-fits the ink colors to the artwork instead of merging the closest pair, so the remaining inks follow the image. Rename any ink, pick a stock name, or type the hex value of the ink on your shelf.

The background and the base. A background color that fills the border is set not to print, and a notice tells you so. Dark inks are left out of the underbase. Every index plate works with the same underbase, choke, trapping, and print-order tools as spot plates.

See the dots before film. In the Plate tab, Output dots renders the selected plate exactly as it will be output: real pixels at the output resolution of 600, 720, 1200, or 1440 dpi. The label shows the plate size in pixels at that resolution, so you can judge how fine the dither will be on film.

Output. An index job generates the same pack as a spot job: one 1-bit film TIFF per plate, unscreened 8-bit channels, the true-size film PDF with registration marks, a preview, and the production ticket. The footer of every film sheet records that the job is an index separation.

How it is built

Built for the press, not the design studio.

The press sets the limits

You enter the screens your press holds, the mesh, and the dot gain you measure. Underbase counts every plate against that budget and thins halftones to match before any film is written.

Film at true size

Every plate lands on the sheet at true size with identical registration marks, center ticks, and a label naming the job, plate, ink, screening, offset, and mesh.

Nothing uploads

Underbase runs entirely on your PC with no account, no telemetry, and no network connections. Customer artwork is only read. One-time purchase in the Microsoft Store.

FAQ

Straight answers—no glossary dump

What is an index separation in screen printing?

An index separation prints shaded artwork with a small set of solid inks by assigning every pixel to one ink and dithering the transitions, rather than screening each ink with halftone dots of varying size. The pattern is very fine, so from a normal viewing distance the mix of inks reads as a blend. Underbase builds index separations with error diffusion and a fitted ink palette.

When should I use index mode instead of spot mode?

Use index mode for JPEGs, soft shadows, glows, and gradients, where colors blend into each other. Use spot mode for clean logos and vector-style art with distinct flat colors. Underbase opens shaded artwork in index mode on its own and shows a notice, and the Separation list switches modes at any time, so you can compare both on the same file in the Composite tab.

Can I control how much the inks dither?

Yes. In index mode the Dither strength field runs from 0 to 100 in steps of 10. At 0 the art is posterized into hard regions of each ink; at 100 soft edges and gradients are fully dithered. The default is 70. Change it and the preview updates, and Output dots in the Plate tab shows the result at the output resolution.

What artwork files does Underbase open?

PNG, TIFF, JPEG, BMP, GIF, WebP, SVG, PDF, and Illustrator (.ai) files, opened with Open artwork, by dropping the file on the window, or from Samples. Vector files are rasterised at 300 dpi at their true size. A raster file's resolution tag sets the print size; when a file has no tag, Underbase uses 300 dpi, flags it, and lets you edit the source resolution or type the print width you want.

Does my customer's artwork stay on my PC?

Yes. Underbase runs entirely on your PC. There is no account, no upload, and no telemetry, and the app makes no network connections. It reads the artwork you open, writes each job to a folder inside the output folder you choose, and keeps its own settings in local app data. Jobs save as .underbase files you can reopen for a repeat order.

How do I get Underbase, and is there a trial?

Underbase is a one-time purchase in the Microsoft Store, and the listing shows the current price in your currency. The Store runs a 15-day free trial, so you can separate a job you have already printed, or one of the six bundled samples, and compare the film with what you burned. The Store installs and updates the app. It runs on Windows 11 version 24H2 or later on x64 PCs.

Related pages

Flat-color tee art, split into one plate per ink. Film positives at true size, with the dots you set. From customer art to film, in one separation app.

Customer art in.
Press-ready film out.

Underbase separates flat and shaded art into spot inks, builds a choked white underbase, traps colors in one click, keeps the job inside your plate budget, and writes true-size film with registration marks and a production ticket. Everything runs on your PC, and the Microsoft Store runs a 15-day free trial.

Pay once. Own it forever.

One-time purchase on the Microsoft Store · No subscription · Instant install

Get it from Microsoft

Buy through the Microsoft Store—instant install, automatic updates, and a Microsoft receipt for easy expensing. No account needed on our site, and no subscription on Store purchases.

Open full product page

Illustrator is a trademark of its owner, registered in the U.S. and other countries. Underbase opens Illustrator (.ai) files as an input format and is not affiliated with or endorsed by the trademark owner.

Technical specifications

Technical specifications for procurement

Spec Implementation
Data Sovereignty Reads only the artwork you open or drop on the window and never writes to it; writes each job (film PDF, TIFF plates, channels, ticket, preview, and .underbase job file) to a folder inside the output folder you choose; settings stay in local app data on this PC
Telemetry Status None; no account, no upload, no telemetry, and no network code in the app
Core Runtime .NET 10 and WPF, self-contained, distributed through the Microsoft Store as an MSIX package; separation, halftoning, TIFF, and PDF output run in the app’s own engine, with PDF and Illustrator (.ai) pages rendered by a bundled PDFium engine
Network Requirements Fully functional offline; the app makes no network connections and nothing is uploaded
Deployment Compatibility Windows 11 version 24H2 or later (10.0.26100), x64; 8 GB RAM recommended for very large artwork, about 400 MB of disk; one-time purchase in the Microsoft Store with a 15-day free trial
Inputs PNG, TIFF, JPEG, BMP, GIF, WebP, SVG, PDF, and Illustrator (.ai) files; vectors rasterised at 300 dpi at true size; print size from the file’s resolution tag or a print width you set, in inches or millimeters
Separation Spot mode (one ink per flat color, close shades grouped, background left unprinted) or index mode (error-diffusion dither between a fitted ink set, dither strength 0 to 100); reduce to 1 to 16 inks; rename, merge, reorder, or switch off any ink
Underbase and traps White underbase from the inks you choose, choke 0 to 3 mm; spread or choke per ink from -3 to +3 mm; one-click trapping of every ink under the darkest; suggested print order with highlight white
Screening Solid or halftone per plate at 10 to 120 lpi, any angle, with tint; ruling suggested from mesh count; dot-gain compensation from 0 to 50 percent; output dots preview at the output resolution
Outputs True-size film PDF with registration marks, center ticks, and plate labels, one plate per sheet or ganged, mirror for emulsion down; 1-bit CCITT G4 film TIFF per plate at 600, 720, 1200, or 1440 dpi; unscreened 8-bit channel TIFFs; production ticket as PDF and JSON; preview PNG; .underbase job file
Film sizes Letter, Legal, Tabloid, Super B, ANSI C, A4, A3, A3+, A2, or a custom sheet up to 60 x 120 in; direct printing to any Windows printer