Intro

A photo engraved into wood or leather looks like magic the first time you see it come off the bed, but the result is mostly math. Your CO2 laser can only burn "on" or "off" at each tiny spot, so a smooth photograph has to be rebuilt from dots and shades before the machine ever moves.

That rebuild is called dithering, and the size of those dots is controlled by your resolution, or DPI. Get these two settings right and even a modest desktop laser will surprise you; get them wrong and you waste an afternoon on a smudged, washed-out tile.

What Dithering Actually Does

Dithering is the trick that converts a full grayscale photo into black-and-white dots your laser can understand. Instead of shades of gray, the software scatters darker dots into lighter areas to fake the look of a midtone, the same idea an old newspaper used for printed pictures.

A real grayscale engraving pass actually varies power slightly to leave lighter and darker burns, but most craft software (LightBurn, LaserGRBL, and similar) rasterizes photos as dithered black-and-white for consistency. The dither pattern decides whether those dots form smooth gradients or visible texture.

Think of it as pointillism with a beam. The closer the dots, the smoother the picture; the sparser they are, the more "dotty" and high-contrast the result becomes. Your job is to pick the pattern and resolution that match the material under the lens.

A smart habit is to cut a dither test strip: a single row showing the same photo rendered in Floyd-Steinberg, ordered, and halftone side by side at your chosen DPI. Ten minutes on one scrap piece teaches you more than a dozen guesses, and you can keep that strip as a reference every time you stock a new material.

Floyd-Steinberg vs Ordered and Halftone

Floyd-Steinberg is the default for good reason. It pushes the rounding error from each pixel into its neighbors, which spreads tones evenly and gives a soft, photographic feel. On wood and leather this is usually the most forgiving choice and the one to test first.

Ordered dithering (sometimes called Bayer) uses a fixed grid pattern. It is faster to compute and very predictable, but it can leave visible regular texture, like a checkerboard shimmer, on smooth surfaces. It works well when you want a bold, graphic look rather than a subtle portrait.

Halftone mimics classic print dots of varying size. It is great for a stylized, comic-book vibe and for materials where you want clear separation between tones, but it can lose fine facial detail compared with Floyd-Steinberg. Try all three on one scrap photo before committing to a big piece.

How DPI Changes Detail and Job Time

DPI, or dots per inch, sets how many burn spots fit along each inch of the image. At 150 DPI a 4x6 inch photo is about 600 by 900 dots; at 500 DPI it is 2000 by 3000 dots. More dots means finer detail, but also a much longer job and a higher chance of scorching.

A useful rule: match DPI to the material grain. Coarse woods and leather look best around 150 to 250 DPI, while slate, anodized aluminum, and finished plywood can take 300 to 500 DPI. Pushing laser DPI past what the material can show just burns longer for no visible gain.

Run a small test tile at a few resolutions side by side. You will usually find a "sweet spot" where detail stops improving, and that is the number to lock in for production. Time saved on every future job easily pays for one afternoon of testing.

Preparing a Photo for the Laser

Start in any free editor: crop tightly, raise contrast a little, and convert to grayscale. Photos with a clear subject and a plain background engrave far better than busy snapshots full of mid-gray clutter.

Brighten highlights slightly and deepen shadows so the dither has clear black-and-white anchors to work from. A common fix is a gentle "levels" or "curves" push so the histogram touches both ends instead of floating in the middle grays.

Size the image to the real engraving dimensions at your chosen DPI before importing it into the laser software. Resizing inside the laser program after the fact can blur the dither and soften the whole picture. Clean source in, clean burn out.

Free tools like Photopea or GIMP handle all of this with no subscription, and phone apps are fine for a quick crop. The point is to export a flat, final-size PNG or JPG so the laser software receives exactly what you prepared instead of re-interpolating it and softening the dots. If the subject has a busy background, cut it out so the beam only works the important part.

Material Starting Points

On photo on wood, try 20 to 35 percent power at 150 to 300 mm/s with 200 to 300 DPI as a starting point, then darken or lighten in 5 percent steps. Softwoods like pine burn faster than hardwoods like maple, so always confirm on scrap.

For leather, keep power lower, around 15 to 25 percent, and speed 200 to 400 mm/s, because the surface chars quickly. A 250 to 400 DPI setting captures grain and facial detail without blowing through the top layer.

Anodized aluminum and slate are where laser photo engraving really shines: 30 to 60 percent power, 100 to 300 mm/s, and 300 to 500 DPI give crisp, permanent images. These are starting points to confirm on scrap material, never final numbers.

On slate coasters, a 40 to 60 percent power, 100 to 250 mm/s, 300 to 500 DPI pass produces a near-photographic stone image that sells well as gifts and memorial pieces. For paper and cardstock, drop to 8 to 15 percent power at 300 to 600 mm/s so the beam scores the surface without burning through the sheet. Match the material's tolerance and the picture stays intact.

Common Mistakes to Avoid

The biggest mistake is cranking DPI to the maximum "for quality." On wood this only lengthens the job and deepens the burn until highlights disappear into a brown smear. Detail stops improving well before the slider hits the top.

Second is skipping contrast prep. A flat, low-contrast photo dithers into mush because there are no true blacks or whites to anchor the pattern. Spend two minutes in an editor and the beam does the rest.

Third is ignoring focus. A photo engraving is unforgiving about a soft beam: if the lens is even a millimeter off focus, fine dots merge and the picture looks foggy. Auto-focus or a ramped focus test on every new material, every time.

Frequently Asked Questions

Can I engrave a color photo directly without editing it?

You can import it, but the software will convert it to grayscale first anyway, and an unedited color shot usually has weak contrast. A quick grayscale plus contrast pass gives a much cleaner result with almost no extra effort.

Why does my photo look speckled instead of smooth?

That is usually ordered dithering on a material that wants Floyd-Steinberg, or a DPI that is too low for the detail. Switch the dither pattern and raise resolution by 50 to 100 DPI on a test tile to compare.

What DPI should I use for a face on wood?

Start around 250 DPI and confirm on scrap. Most woods show no extra detail above 300 DPI, and going higher just risks scorching the highlights while tripling the run time.

Do I need a special laser to engrave photos?

No. Any desktop CO2 laser that can run a grayscale or dithered raster will do it. The skill is in the image prep and settings, not in the machine, which is why so many makers start with photo gifts.

Should I engrave or cut a border around the photo?

If you want a freestanding tile, cut a thin outline after the engrave so the picture sits in a clean frame. Run the engrave first, then the cut, exactly like any combined job, and the border neatly hides the softer outer dots where the dither fades.

Ready to turn your own photos into keepsakes? Browse the desktop machines and settings help on the Redsail Laser cutter page, and if you are comparing brands for a small shop, this guide to CO2 laser cutters at https://www.hflaser.com/laser-cutter.html is a handy side-by-side reference.