How to prepare an old photo for laser etching on granite

Most photos families bring in were never meant for a stone. They are small prints from decades ago, wallet photos with cracks, or a phone picture of a framed print. A laser on black granite is not forgiving. Scratches, specks and blur all get etched. This guide covers what to do before the file goes to the laser, in the order we recommend.

1. Get the best original you can

• Ask for the original print, not a phone photo of it. A phone photo adds glare, skew and blur.
• Scan prints at 600 dpi. One wholesale etcher's published price book asks for 600 dpi scans of prints, and 300 dpi or more for digital files.
• Ask for every good photo of the person. A second photo helps you check the face after editing.
• If the person is small in a group photo, only the pixels around their face count. A face that is 200 pixels wide will not make an 11×14 portrait.

2. Check that the photo is big enough for the size

What matters is how many photo pixels land on each inch of stone. Aim for 150 to 300 photo pixels per inch at the final size. Below 150, detail starts to go soft.

These are the pixels in the cropped portrait, not the whole photo. If the photo is too small, you have three choices. Etch a smaller size. Upscale it. Or tell the family the quality is limited and have them accept it on the proof. Some wholesale etchers already ask clients to acknowledge the risk of a poor photo.

AI upscaling (2 to 4 times) helps, but it adds detail that was not in the photo. Use a gentle setting that stays close to the original, and compare the face carefully.

3. Repair the damage

Fix scratches, cracks, specks, stains and fading before anything else. Every mark left in the photo becomes a mark on the stone. Retouching by hand in Photoshop works, but it is slow. One wholesale etcher's 2023 price book lists photo touch-up at $200 an hour. AI restoration does most of this in seconds. Either way, look closely at the eyes, mouth and hairline afterwards. Those are the places where a repair can change how the person looks.

4. Deal with the background

Busy backgrounds compete with the face on stone. Engravers on the LightBurn forum strongly recommend removing the background. A plain dark background is the simplest choice for black granite. Dark areas are not etched, so the background disappears into the polished stone and the face stands out. If the family wants a scene, add it as a separate step once the face is final.

5. Convert to grayscale and set the tone for stone

Granite does not show pure white or pure black well. Bright areas tend to over-burn, and dots "grow larger and may overlap," which Trotec calls dot bleed. Deep shadows lose their detail. These starting points come from vendor guides and the LightBurn forum:

• Keep the tones away from the extremes. Map the image to roughly 8 to 245 instead of 0 to 255.
• Lift the shadows a little, so dark hair and dark clothing keep some detail.
• Lighten the midtones. LightBurn's developer has suggested a gamma of about 0.8 for granite.
• Sharpen with a larger radius than you would for print. A small visible halo survives dithering on stone. Fine sharpening does not.

These numbers are starting points, not rules. Every stone and machine is different, which is why the test in step 7 matters.

6. Save it at final size, and keep it positive

Save the file at the final size in inches, with the DPI written into the file. For a CO2 laser on black granite, 200 DPI is a common starting point. See the DPI guide for other lasers.

Keep the file positive. It should look like a normal black-and-white photo. LightBurn's Negative Image option and PhotoGrav's Black Granite setting invert the image themselves. If you invert it too, it gets inverted twice and etches as a negative.

Send a grayscale file, not a pre-dithered dot file, unless your setup needs one. Grayscale can be resized and re-dithered at the machine. A dot file only works at the machine's exact DPI, and resizing it ruins it.

7. Test on scrap stone first

Etch a test strip on an offcut of the same granite: a grey scale from black to white, plus a small crop of the face. It shows where the stone starts to mark, where it burns out, and whether the DPI is right. Adjust the tone, then etch the memorial.

How Stone Portrait does it

Stone Portrait runs these steps in one place. Upload the scan, repair scratches and fading, replace the background, and pick the size, shape and laser type. The page warns you when the photo has fewer than 150 pixels per inch at that size, and offers a gentle AI upscale. You download a positive grayscale PNG with the DPI embedded, a test strip, and a proof for the family. The presets are starting points from laser vendors and the LightBurn forum, not results from your stone, so test first. You can start a free trial with three portraits.