DTF White Halo Choker
Shrink your white underbase mask so it sits inside the color edge. Upload one transparent PNG, or a color layer plus a white mask. Set the choke in pixels, check the removed edge in magenta, and download a transparent white mask for your RIP. Free, and it runs in your browser, so your files are not uploaded.
1. Choose a workflow
One PNG builds the white shape from your artwork. Two files shrink a white mask you already have.
2. Upload your design
PNG with a transparent background. The edge of the design is read from the alpha channel.
2a. Color layer
Your artwork as a PNG with a transparent background.
2b. White mask
Bright pixels count as white ink. Same pixel size as the color layer.
3. Settings
Start with the defaults, press one test transfer, then adjust in single pixel steps.
Physical shrink: 0.25 mm at the DPI shown.
The DPI value only drives the millimetre readout.
How opaque a pixel must be (0 to 255) to count as design. Lower values treat soft edge pixels as solid. The default of 50 suits most artwork.
Transparent white mask
Choked and ready for your RIP. Shown on a dark background so the white is visible.
Halo proof
Magenta marks the white that was removed from the edge.
What is a white halo on a DTF transfer?
A white halo is a thin white fringe around the edge of a pressed DTF design. It shows most on dark and colored garments, and it appears when the white ink layer reaches past the edge of the color layer. The white prints on top of the color, so after pressing it sits between the color and the fabric, and any white that overhangs the color is visible from the front.
Common causes are a white layer generated slightly larger than the artwork, soft or semi-transparent artwork edges that get converted to solid white, and small registration or ink spread differences between the color and white passes. A choke corrects a small overhang. It does not fix a printer that is badly out of register.
How does choking the white layer fix it?
A choke shrinks the white layer inward by a set number of pixels, so the color layer overhangs the white by a small margin and hides it. This tool shrinks the shape with a round brush, so every edge moves in by the same distance, including curves and corners. Before this, the choke meant building the white channel by hand in an image editor, or finding the choke setting in your RIP, if it has one, and repeating the test prints.
How much should I choke the white layer?
Start at the default of 3 px, which is about 0.25 mm at 300 DPI, press one test transfer, and adjust in single pixel steps. Choking too far leaves a rim of color with no white underneath. On dark garments that rim looks thin or dull because the fabric shows through the color. The same pixel value is a different physical distance at other resolutions, so watch the millimetre readout in the tool.
What does the tool do to my file?
- One PNG mode reads the alpha channel. Pixels with alpha above the Alpha Threshold count as design, everything else is background.
- Two file mode reads the color layer the same way. The white mask counts as ink where it is brighter than the threshold, weighted by its own transparency. Bright means ink, so a mask that uses black for ink needs inverting first.
- The white shape is shrunk by the choke amount. In two file mode white is only removed, never added: the result is your white mask minus the edge band.
- Edges of the image canvas are not choked, so a design that touches the canvas edge keeps its white there.
- The download is a white PNG whose transparency carries the shape, with hard edges and no anti-aliasing. The proof shows your color layer with the removed pixels in magenta.
- If your PNG carries a DPI tag, the downloads carry the same tag. If it does not, the downloads have none. The DPI field only drives the millimetre readout.
- Processing happens in your browser and files are not uploaded. The limit is 64 million pixels per file.
Frequently asked questions
What does the DTF White Halo Choker do?
It shrinks a white underbase mask inward by 1 to 10 pixels so the color layer overhangs it and hides white fringing at the edge of a DTF transfer. You get a transparent white mask PNG and a magenta proof that shows exactly which pixels were removed.
Are my files uploaded anywhere?
No. The tool runs entirely in your browser and your PNG files are never sent to a server. Closing or reloading the page clears them.
What does the Alpha Threshold setting do?
It sets how opaque a pixel must be, on a scale of 0 to 255, to count as part of the design. At the default of 50, pixels that are more than about 20 percent opaque count as design. Lower values treat soft, faint edge pixels as solid. Higher values ignore them and pull the edge inward.
Why does the tool say my PNG has no transparency?
The tool finds the edge of your design from the alpha channel. A PNG with a solid background has no edge to find, because every pixel is opaque. Remove the background, export a PNG with transparency, and try again.
Does the downloaded mask keep the size and DPI of my file?
The pixel size is identical to your input. If your PNG carries a DPI tag, the downloads carry the same tag, so the white mask lands at the same physical size as the color layer in your RIP. If your file has no DPI tag, the downloads have none either.
How large a file can it process?
Up to 64 million pixels, for example 8,000 by 8,000 pixels. Larger files are refused with a message instead of crashing the tab. Phones and tablets have lower browser limits, so use a desktop browser for big files.
Related on Printing TLDR: the DPI checker and the DTF printing tools hub.
Need the rest of the DTF prep in one place?
DTF Toolbox is a separate product built by Kjell Karlsson, not part of Printing TLDR editorial. It is a subscription suite of browser-based DTF prepress tools, including a gang sheet builder, with a free tier per tool. This choker stays free.
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