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I have bought a digital USB microscope:

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Which can take images like this:

enter image description here

I would like to measure – as accurately as possible – the width of the white line on screen, as you see in the picture.

Problems I'm having with the software:

  • A ruler for Windows - Only measures in pixels
  • JRuler - Only measures in mm.
  • Paint.net - Only measures in mm.
  • Photoshop - Divides mm in 5 which is quite good but not enough (not counting the price since it will only be used for measuring every now and then).

Is there a (preferably free) software that can measure with a precision of at least 1/10th of a millimetre?

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What do you mean by the "width"? Surely the physical width versus the apparent width is dependent on the magnification you are using and the distance between the object and the imaging ccd? –  Paul May 23 '12 at 1:09
    
If you know the pixels, then you can convert that depending on the magnification by yourself, no? –  soandos May 23 '12 at 1:36
    
@soandos Then "only measure in pixels" would not be listed as a problem –  Paul May 23 '12 at 1:42
    
@Paul, I don't see the difference is all, and was asking him to explain it. –  soandos May 23 '12 at 1:43
    
@Paul I had the misconception, that I could convert from screen pixels to metric directly. –  Trufa May 23 '12 at 3:51
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1 Answer

up vote 1 down vote accepted

Most Computer displays now regardless of resolution are displayed at 96 dpi or dots per inch. ( THe Retina scan displays are much higher) You can change this ( I recall) in Windows desktop> preferences> advanced to say 100 dpi. for readings in thou" but since you (& I) prefer metric and your microscope has variable zoom, your exact µm per pixel will require calibration using a ruler. So use Irfanview to zoom [+/-] and measure a rectangle with mouse which is displayed in status bar.

Iview.exe also is free from corel or http://www.irfanview.com and has many add-ons and supports many including Adobe effects if you have any. Its not hard to use calc.exe Also Irfanview has easy sharpen and adjust color size and save options, as well imports directly from scanners and any TWAIN device, such as scopes, cams.

I might suggest a clear mylar grid that is precise if you maintain temp and RH, for measurements. YOu can buy this or get it printed onto film or by lithographic printers.

Laser interferometry methods can be even more precise than you need.

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