To evaluate skin pigmentation in different skin layers, a special light adapter is needed to take multispectral pictures of the skin. As there are different optical properties of skin pigments, four different light sources have been chosen.
- blue λ= 470 nm – highly absorbed by epidermal melanin
- green λ= 576 nm – hemoglobin peak
- red λ= 660nm – epidermal-dermal boundary
- IR λ= 865 nm – low absorption, sensitive to scattering to measure papillary dermis thickness.
There was a lighting source for the “Nikon Coolpix E3100” digital camera developed to take multispectral images of skin.
Making an adapter
The drawing of lighting adapter
The lightning adapter isn’t tough to build. It would help if you made a circular PCB and solder LEDs with protective resistors. The PCB image:
Then soldered LEDs symmetrically to distribute the smooth light:
LED’s are in a row: Red, Green, Blue, and IR, White. White LED is optional to make normal pictures of skin.
Then I made a hole for camera optics. It also serves as the holder of PCB. As you see in LEDs, I put a polarizing filter (another is placed on optics of camera with polarization axis crossed to this one). This filter is used to filter light reflections from the surface layer of skin to remove flares. Then you get the image of deeper skin structure.
The beautiful shiny LEDs are working:
Testing an adapter on a skin
I had some problems to focus them on one spot. LEDs have not ideal characteristics, and they weren’t ideally soldered to board. You can see my effort 🙂
I only needed one square centimeter of the region to be smooth lightened.
The finished adapter:
About skin reflectance modeling, there are other topics created, and you’re welcome to read them. There I will put a few impressive results about taking photos of skin and lesions.
Here are the matrices calculated for each color. They are subtracted from every picture I made to suggest that lighting is equal to all points on the 1x1cm region:
Let’s make some test shots:
First test results
I didn’t make Infrared here, as this lesion is benign and doesn’t show any skin structure changes.
Suspicious lesion as you can see Infrared (fig e) picture shows the view from deeper skin layers:
And here you can see parametric maps generated using a model with these images:
Here are images with hair and benign lesion:
As this light adapter is hand made and calibration is weak, there can still be good results. This experiment proved that a handheld digital camera and simple lighting adapter could show relative diagnostic results while inspecting skin lesions.