Measuring in a photo

Discussion in 'Digital Photography' started by iNewbie, May 1, 2008.

  1. iNewbie macrumors regular

    Aug 25, 2006
    Does anyone know of any software that will allow you to measure inside a photo?

    For example, I there was an object in the picture that I knew was a certain size, I'm looking to find out the size of another object.

    Any ideas would be appreciated.
  2. ChrisA macrumors G4

    Jan 5, 2006
    Redondo Beach, California
    Adobe Photoshop Extended CS3. The "extended part" is for measurring and 3D work. Adobe will let you download and try it free for 30 days. See
  3. Abstract macrumors Penryn


    Dec 27, 2002
    Location Location Location
    Just use ratios.

    If you know the length of one object, how many pixels is that in the photo? Use the ruler tool to find out.

    When you divide one by the other, you'll get: # of pixels/length of object. In other words, you'll know how many pixels in the photo will represent 1 cm/metre/inch/foot, etc.
  4. iNewbie thread starter macrumors regular

    Aug 25, 2006
    Thanks for the response. When you say ruler tool, what application are you referring to? Photoshop?

    I thought of doing the ratios and will use that as a fall back method, but I was hoping to find some software for comparison. This picture might be involved in a court case for my company.
  5. jampat macrumors 6502a

    Mar 17, 2008
    The ratios trick only works for objects that are the same distance from the camera (and if it's a wide angle lens, it only works for objects close to each other as the distortion around the edges will cause problems). There are commercial software packages to do what you require and if this measurement may end up in court, it may be worth finding one (or even better, a company that has experience with the software and can testify as an expert witness at trial). There is a special name for what you require, but I can't remember what it is.

    Good luck,

  6. AxisOfBeagles macrumors 6502


    Apr 22, 2008
    East of Shangrila
    Jampat's reply is important - objects would need to be center framed, near one another, and equidistant from the lens - otherwise using image ratios will mislead you.

    For a rough estimate, that would be fine - but for use inn a court case? You'd better get some software designed for the purpose.
  7. ChrisA macrumors G4

    Jan 5, 2006
    Redondo Beach, California
    In almost all photo the pixel/foot ratio is not constant and is a function of (x,y) and in many places the "ratio" is a not-linear function.

    One simple example: Stand at eye level and take a picture of a round man-hole cover in the street. On the computer monitor the cover will look like an elipse if the camera was aimed directly at the manhole cover but a more complex shape (not even a "conic") if the cover is off center

    And this is only perspective distortion, next we can talk about lens distortion. It is not an easy subject.

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