How to prepare images for optimal engraving

[FAC]

Photo tips:

Look for images with WHITE backgrounds if you are engraving in wood.

Look for images with BLACK backgrounds if you want to engrave in anodized aluminum or marble or granite.

Image conversion using Photoshop:
1) Convert image to grayscale by Image\Grayscale
2) Image\Auto Tone
2) Image\Adjustments\ Brightness\Contrast and adjust contrast all the way up. Remember what you see on the screen and what you see on the end product is not the same. Most photos need contrast to be increased to work well.
3) Image\Image Size -> Set Document Size to the size you want to engrave. Set Resolution to 1000 dpi.
4) Image\Mode -> Set Output to 500 pixels/inch or 250/pixels inch. Method Use: Diffusion Dither. Setting resolution lower in this step then higher will "block" the image so the laser stays on longer giving stronger details.
5) Image\Image Size -> Change resolution to 1000 pixels\inch. Choose Nearest Neighbor (preserve hard edges). Note if you zoom in all the way, now the pixels are actually blocked to 4x4 (if you selected 250/pixels inch in Step 4) or 2x2 (if you selected 500/pixels inch). RetinaEngrave's native resolution is 1000dpi but the laser power supply often cannot be switched at that high a speed so you want to block the image so that neighboring pixels have the same color in order to have an accurate dithering. Don't worry about the pixelled look to the image because the laser beam will have a gaussian blur effect after you engrave it.
6) Image\Invert if you want to engrave in granite; otherwise, skip this step.
7) File\Save As -> Change format to BMP and choose Depth=1 Bit and Ok. RetinaEngrave will work with direct print at this point but we recommend you save it as a bitmap file and open the bitmap in RetinaRaster. The reason for this is that we have carefully prepared every pixel position in the image and RetinaEngrave is 100% pixel perfect. If you use direct print, Window's print system will scale the image to print resolution and use some sort of interpolation of pixel values.
8) Engrave the image. Use lower powers and slower speed for more detail. Follow the guidelines set in the samples thread. Don't worry if the image looks pixelated in the preview - it will come out ok. Make sure your laser is in focus or else hard materials like granite will not engrave. We measure 2.32" using a digital depth guage from the top surface of the laser head plate to the engraving surface.

Additional notes: if you want the absolute best results, reduce power to 5-10mA or less and reduce speed to 5-10% and engrave at 1000dpi. This takes a lot longer but at low powers and speeds the laser operates without the higher order lasing modes which are undesirable for engraving (much higher M2 beam quality). Also use a 1.5" lens. This greatly increases quality due to the reduced spot size from the lower M2 and optics. We have tested this carefully using advanced CO2 laser sensors.

[Tomason]

Thanks for the suggestions.
I have also found that it is best to select a picture that was created using a flash, or a picture that does not have any shadows on the main subject of the photo.
I have created good engravings on granite by making a negative of the image using the Photoshop Image-Adjustments-Invert command. That allows me to use the same image on granite that I use on wood.