In order to evaluate skin pigmentation in different skin layers, there is a special light adapter needed to take multispectral pictures of 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 lighting source for “Nikon Coolpix E3100” digital camera developed to take multispectral images of skin.
The drawing of lighting adapter
The lighting adapter isn’t very hard to build. You need to make 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 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 front of LEDs, I put a polarized 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:
I had some problems to focus them to 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, 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 make a suggestion, that lighting is equal to all points on the 1x1cm region:
Let’s make some test shots:
I didn’t make Infrared here, as this lesson is benign, and doesn’t show any changes in skin structure.
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 still can be good results obtained. This experiment was made to prove, that a handheld digital camera and simple lighting adapter can be used to show relative diagnostic results while inspecting skin lesions.