103: Halftoning Wood

This week I had a challenge that I’ve been dreading for a while now: recreating a greyscale image on a wood surface. While engraving a black and white design results in impressive, high-contrast finished pieces, any images with a wide variety of values can end up looking muddy if you don’t properly determine how the laser’s halftoning process affects the greys in the image in question.

The complete memorial plaque.
The complete memorial plaque.

For this project—a memorial plaque for a family member who recently passed on—I was using a picture of a lighthouse overlooking a beach paired with one of his enduring quotes. While the text itself was easy black-on-white engraving, the photograph was a full color piece that I had to do some editing on before it could be ready for the laser.

The first engrave test on scrap material had nearly no contrast between greys.
The first engrave test on scrap material had nearly no contrast between greys.

I’ve had more luck with a smaller amount of grey shades than with a fine gradient, so I used a posterize command to reduce the shades down to three or four (including black and white). That was easy enough, but the tones had too much contrast at first, resulting in most of the greys looking all but identical to black on the wood. A few level adjustments brought most of the greys near the center of the spectrum, which proved after several more test cuts be the right level of contrast for this particular wood.

The final test engrave, smaller than the others to save space, shows a good contrast.
The final test engrave, smaller than the others to save space, shows a good contrast.
The layout shows how narrow and toward the center of the grey spectrum the photo engraving needed to be.
The layout shows how narrow and toward the center of the grey spectrum the photo engraving needed to be.

That’s one of the trickier bits, too: different woods produce different results. This wood is unfinished, and will darken to some degree no matter how much power you throw at it, but some finished woods can actually lighten in color with lower power engraves before burning into the wood with higher settings. Even another unfinished piece of wood from a different type or batch could engrave lighter or darker than the results here. You’ll want to have tight control over the source (and thus consistency) of your material, otherwise you’ll have to fuss with grey levels regularly or suffer through inconsistent engraving quality on the finished product.

A closeup to show off the halftone pattern through various shades of grey.
A closeup to show off the halftone pattern through various shades of grey.
Engrave too far into this particular wood stock and you'll reach the next ply, significantly altering the look. A neat effect if you can control it!
Engrave too far into this particular wood stock and you’ll reach the next ply, significantly lightening the surface. A neat effect, if you can control it!

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