This is a scanning recipe for advanced users to scan sheer or lace fabrics and create an alpha map (also known as an opacity map).
Setup
Create a backlight for scanning that is large, flat, bright and even.
- Large: enough to cover the entire chart window for the scan size you want to work at
- Flat: flat surface strong enough to hold the fabric and chart
- Bright: enough to dominate the room lighting and give a well exposed image at ISO 100 1/200s f/16
- Even: the brightness should not vary by more than 0.1 stop across the chart window, and should be free of any small or medium scale structure
- Diffuse white:
- the colour temperature of the backlight illumination should match the colour temperature of the on-camera flash,
- diffuse reflection from the backlight surface should be white (flat spectrum like a white balance card), and
- the backlight surface reflection should be matte (not glossy)
Good options to create the backlight:
- LED panel video light (e.g. Godox ES45 works well for A4 scans)
- Softbox
Good options for the diffuser:
Things to avoid
⚠️ Avoid using a diffuser with visible fabric weave or any blotchiness as these variations will come through in the alpha channel and make seamless tiling difficult.
⚠️ Avoid using a diffuser with a glossy surface, as the shiny reflections will interfere with scan processing.
Scanning
| Step |
Shots |
On-camera flash |
Backlight |
Fabric |
Chart |
Filename suffix |
| Standard scan |
9 or 25 |
On |
Off |
Yes |
Yes |
|
| Alpha |
1 |
Low |
On |
Yes |
Yes |
opacity |
| Alpha calibration |
1 |
Low |
On |
No |
Yes |
opacity-cal |
- Put the fabric you want to scan and your Bandicoot chart on top of the backlight