What to know first

  • DPI and line interval describe the same scan spacing in different units.
  • The useful value is limited by laser spot size and material response, not by the source photo alone.
  • Too much density can add heat, time, darkness, and muddiness without adding detail.
  • Prepare the pixel grid for the final physical size and preserve that relationship after export.

DPI and line interval are linked

DPI describes how many scan positions fit in one inch. Line interval describes the distance between adjacent scan lines, commonly in millimeters. They are two views of the same spacing.

The conversion is DPI = 25.4 ÷ line interval in millimeters. A 0.10 mm interval corresponds to 254 DPI. A 0.08 mm interval corresponds to about 318 DPI. Changing one changes the other.

Workshop note: Useful conversions: 0.20 mm = 127 DPI, 0.15 mm ≈ 169 DPI, 0.10 mm = 254 DPI, 0.08 mm ≈ 318 DPI.

Sources: 1, 2

Higher DPI is not automatically more detail

A laser mark has physical width. Material also spreads, chars, melts, fractures, or changes color beyond the mathematical centerline. When scan lines are placed closer than the process can resolve, they overlap. The result can become darker and muddier while the job takes longer.

At the other extreme, an interval larger than the effective mark can leave visible gaps and make the image light or striped. The useful target is where neighboring lines create continuous coverage without excessive overlap.

Sources: 1, 2

Find the interval from the machine and material

Use a purpose-built interval test or a controlled gradient on the actual material. Keep focus, speed, power, lens or module, and surface preparation fixed. Inspect the result under magnification when possible.

Look for lines that just meet. If the surface response changes with power, interval and power may need to be tested together, but record each combination. A value that works for birch plywood with one diode module may not transfer to slate, glass, coated metal, another focal length, or another batch.

  1. Choose a narrow rangeStart around values recommended by the machine maker, then include spacing on both sides.
  2. Hold the file constantUse one gradient or prepared crop so the image does not become another variable.
  3. Inspect coverageFind the widest interval that avoids visible gaps and still preserves the intended tone range.
  4. Record the processSave material, finish, focus, speed, power, interval, and date together.

Sources: 2

Calculate the pixel dimensions before dithering

For an externally prepared bitmap, physical size and intended DPI determine the pixel grid. Multiply inches by DPI. A 3.5 inch wide engraving at 254 DPI needs 889 pixels. If working in millimeters, divide width by 25.4 and multiply by DPI.

Height follows from the crop aspect ratio. If the image is 4:5 and the width is 1,000 pixels, the height is 1,250 pixels. Prepare and dither that final grid rather than creating a huge binary image and asking the laser software to shrink it later.

Workshop note: Pixel width = inches × DPI. Inches = millimeters ÷ 25.4.

Sources: 1

Do not confuse DPI metadata with pixel data

An image file contains a fixed number of pixels. It may also contain resolution metadata that suggests a physical print size. Importing software can honor, ignore, or reinterpret that metadata. The reliable check is the combination of pixel dimensions and the physical width shown in the destination.

If a 1,000 pixel image should run at 250 DPI, its intended width is 4 inches. Confirm both values after import. Do not assume that a file labeled 300 DPI will automatically arrive at the correct size in every program.

Why resizing a dithered image is risky

A grayscale image can be resized before dithering because the new pixels still represent continuous tones. A one-bit image is different: each pixel is already a decision. Interpolation can create gray pixels, remove isolated marks, or duplicate them, after which another threshold or dither may alter the pattern again.

If the job size changes materially, return to the nondithered source, calculate a new pixel grid, and dither again for that size. This is more reliable than scaling the finished dots.

Sources: 1

A pre-burn resolution checklist

Before running the job, confirm the physical width and height, source pixel dimensions, intended DPI or interval, and destination settings. Preview closely enough to see whether the image still contains the expected dot pattern.

  • The interval was tested for this laser, material, focus, and finish.
  • The bitmap was generated at the final intended dimensions.
  • The imported physical size matches the preparation size.
  • No second dither or resampling step is active.
  • A representative crop has been tested on scrap.

Sources: 1, 2

Common questions

What DPI should I use for laser engraving photos?

Use the DPI that matches a tested line interval for your laser, focus, and material. LightBurn suggests testing roughly 120 to 300 DPI as a starting range in its photo guide, but the correct value is process-specific.

What is 0.1 mm line interval in DPI?

A 0.10 mm line interval is 254 DPI because 25.4 divided by 0.10 equals 254.

Why does high DPI make my engraving dark?

A higher DPI places scan lines closer together. If the physical marks overlap, the surface receives more energy and neighboring details merge.

Sources and further reading

Technical claims were checked against current first-party documentation. Product interfaces and guidance can change, so confirm the current documentation for the software and machine you use.

  1. 5 Steps to Perfect Image EngravingsLightBurn User Guide. Checked August 2, 2026.
  2. Interval TestLightBurn User Guide. Checked August 2, 2026.
  3. Image ModeLightBurn User Guide. Checked August 2, 2026.