Data Structuring: How to Take a Standardized Clinical Picture for Computer Vision in Dermatology

  • Taking a standardized clinical picture can help to compare images and enhance machine learning to recognize the conditions, especially when associated with clinical data.
  • It is also of use when images want to be used later in publications, research and presentations
  • The following points mention the specific factors to take into account when doing photography, and remains of course applicable in clinical photography:
  • Focus
    • Before, mobile phones, when we had to use Single-lens reflex (SLR) cameras, maybe this was an important issue because it’s not so obvious using a manual focus to get the right focus of an image. Nowadays, fortunately, with mobiles, we just have to touch the screen and you focus an image.
  • Depth of Field
    • In Dermatology we are looking to see as many layers as we can so the depth of field should be as large as possible. Note that the smaller, the aperture (diameter of the lens for image capture), the larger the depth of field…so mobile phones are a pretty good thing !
    • On the other hand, with a shallow depth of field, you will only focus on one part of the body.
  • Color Calibration/white balance and Light (illumination)
    • It is what makes an image appear. And is based on “white”.
    • What is white looks white…sounds obvious
    • For example, let’s take a picture of a table in the evening. If you have the bulb of your living room on, you’ll see that what is white looks yellow because different bulbs change colors.
    • This also happens when you take your pictures from your patients:
      • If you’re using natural light, but it’s a cloudy day, you will get bluish tones.
      • If you have very sunny days, you will get a lot of shadows.
    • In conclusion getting the right color is extremely important because we make diagnosis based on color. So be careful about the lights that you use and how you illuminate the subject.
  • Resolution
    • Always images need to be taken with the highest resolution because we need those images to be good, because we want to use them eventually for a publication so we want them to be of high quality.
  • Backdrop
    • this reduces distractions. A blue-green backdrop can also help with color calibration and is effective in photography of black skin.
    • “Distractions”: Also remove distractions on the patient such as Earrings, makeup, glasses, etc…
  • Field of View
    • The field of view means that you need to take different distances of the lesion. For instance, if you have a tumor and you take a closeup, which is a very important image, you also need to take a picture farther away because you want to see that tumor in relation to the anatomical area. So that you’re capable of understanding if that tumor is amenable to be treated in one way or another, because at a three millimeter tumor or it’s a one centimeter tumor.
    • As a piece of advice you could take a picture 10cm from the lesion and 25cm away, taking the picture directly over and at an angle of 45 degrees.
  • Position
    • Positions need to be always the same so that you can monitor and compare. B And this lady has been taken in the same position, exact same position, but with different lenses.
  • Scale
    • It’s important to use a scale, especially when you’re using and treating tumors.

Paola Pasquali, MD. Digital Photography for Teledermatology Systems and Devices. 8th World Congress of Teledermatology, Skin Imaging and AI in Skin diseases – November 2020


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