Laser settings
Best DPI for photo etching on black granite
DPI by laser type for portraits on black granite, what dot pitch means, why CO2 lasers need a lower DPI, and how to find your own number with a test strip.
6 min read · Updated November 9, 2026
Short answer: lower than most people expect. For a CO2 laser on black granite, start around 200 DPI and test between 125 and 250. Fiber and diode lasers can go higher. The right number depends on your laser's spot size, lens and power, and on the stone. Treat every figure here as a starting point.
Why higher DPI is not better
On a laser, DPI is the spacing of the lines and dots. At 200 DPI the dots are 0.127 mm apart. If the laser's spot is wider than that, neighboring dots overlap. Trotec describes this as dot bleed: dots "grow larger and may overlap." On granite, overlapping dots merge into flat white patches, and the midtones disappear. More DPI also puts more heat into the same area, and granite is easy to over-power. Another common piece of advice is "less is more."
A LightBurn forum user put it simply: usable resolution is set by the spot size and the material. LightBurn's developer has suggested 120 to 180 DPI for a 120 W CO2, and about 250 DPI for an 80 W. He also notes that a longer lens means a lower DPI.
What sources report, by laser type
| Laser | DPI reported on black granite | Notes |
|---|---|---|
| CO2, high power or long lens | 120–200 | One vendor: "do not try higher than 150" unless experienced; 125 for large monuments |
| CO2, 80–120 W | 120–250 | LightBurn forum, from LightBurn's developer |
| CO2, 35–50 W desktop | 200–400 | Epilog white paper and forum reports; one 40 W user with a 1.5 in lens ran 500 |
| MOPA fiber | 500–600 | Vendor claim, "up to 1200" |
| Diode, 10 W | about 250 | One forum report, unverified |
Most of these come from vendors and forum posts, not controlled tests. They agree on the direction: big CO2 machines run lower, and fine-spot lasers run higher.
Dot spacing at common settings
| DPI | Dot spacing | Pixels in an 8×10 file |
|---|---|---|
| 125 | 0.203 mm | 1000 × 1250 |
| 200 | 0.127 mm | 1600 × 2000 |
| 250 | 0.102 mm | 2000 × 2500 |
| 500 | 0.051 mm | 4000 × 5000 |
Compare the dot spacing with your laser's spot size. If the spot is clearly larger than the spacing, lower the DPI.
Size beats DPI
A portrait looks sharper because it has more dots in total, not because the dots are packed tighter. One vendor puts it as "human eyes see total pixels, not dpi." An 11×14 at 150 DPI has more dots than an 8×10 at 200 DPI, and people view it from further away. If a portrait looks rough, going up a size often helps more than raising the DPI.
Grainy or colored granite shows less detail. Vendor advice is to etch it larger, at a lower DPI (about 125), with more power and white highlights. For grey or colored stone, many shops etch a black granite insert instead.
File DPI versus machine DPI
If you send a grayscale file, the DPI stored in it mostly sets its physical size. The laser software dithers it at whatever DPI you choose, so you can still change your mind at the machine.
A pre-dithered 1-bit file is different. Epilog's advice is to make sure your driver resolution matches the file's resolution. LightBurn's Pass-Through mode locks the DPI to the image size. A dot file made at the wrong DPI, or resized later, etches badly. That is why we recommend grayscale as the main file.
Don't confuse laser DPI with photo detail. The photo should still have 150 to 300 of its own pixels per inch at the final size. See preparing an old photo.
Find your number with a test strip
- 1.Etch a test strip on an offcut of the same stone: a grey scale in 11 steps, plus a crop of the face.
- 2.Run it at two or three DPIs. On a CO2, for example, try 150, 200 and 250.
- 3.Look at it from normal viewing distance, then up close. Note which grey steps merge into white and which stay bare.
- 4.Pick the DPI where the midtone steps are still clearly different from each other.
- 5.Set your lightest and darkest tones to the steps that still show a difference.
- 6.Write the result down for that stone and that machine.
How Stone Portrait does it
Stone Portrait has presets by laser type: CO2 on black granite at 200 DPI, MOPA fiber at 500, diode at 250, and grainy stone at 125. The stone preview estimates how the dots spread, and a 4× zoom shows the actual dots before you export. Every portrait comes with a test strip at the DPI you picked. The presets are starting points from laser vendors and the LightBurn forum, not tested on your stone, so run the test strip first. Read LightBurn settings for granite portraits next, or start a free trial.
Questions
Is 300 DPI good for black granite?
For many CO2 lasers it is too high. Sources report 120 to 250 DPI for 80 W and larger CO2 machines. Smaller desktop CO2 lasers often run 200 to 400. Test on an offcut before you decide.
What DPI should the photo itself have?
That is a different number. The photo needs about 150 to 300 of its own pixels per inch at the final size. The laser DPI is set in the file and in the laser software.
Does a fiber laser need a different file?
No. Use the same positive grayscale file and set a higher DPI in the laser software. A vendor claims 600 DPI on MOPA fiber. Treat that as a claim until your own test strip confirms it.
What DPI should I use on grey or red granite?
Lower, about 125, and etch the portrait larger. Detail is harder to see on grainy or colored stone. Many shops use a black granite insert for the portrait instead.