On Sat, Jan 02, 2021 at 05:24:15PM +0530, Sonali Warunjikar wrote: > If I imagine line pair to be equivalent of 2 pixels, the pixel width isn't > matching with that. Essentially lp/mm is appearing coarser than pixel > width and probably hence called 'true (measured) resolution' and may be > they aren't expected to match. > > I tried both: 1. using pixel width compute pixels per meter 2. using > lp/mm, assuming 1 lp is equivalent to 2 pixels compute pixels per meter. > > The latter is coming closer to the reality, but not sure it's accurate > enough as yet. May be there was a gap between the finger and the sensor > when trial x ray was taken as our attention was on usb interface rather > than lengths (getting computed length smaller than the actual one of the > portion of the finger). I need to go and gather more x rays carefully (may > be using a coin to make the boundaries more accurate) before confirming > which measure is accurate or whether something else is required or is just > a fixed calibration factor is needed.
[1] is the image produced by a coin kept right on the sensor whose diameter is officially 21.93mm (appears 22mm to us by accuracy with which we can measure at home). The spec[2] says: pixel size = 19 micrometer, 'true (measured) resolution = 16 linepairs/mm. The png encoder requires pixels/metre by pixel size it comes out to be: 52631 by lines per mm it is (explained above): 32000 I measured the count of pixels along diameter line using gimp, by drawing a line that to a naked eye looks like a diameter. It comes to be 1172. So pixels/m should be diameterpixels * 1000/21.93 = 53442.77. This is closer to the one derived from pixel size, but quite far from linepair/mm. Can someone suggest any better way (preferably some tool) to measure the diameter of the circle in image [1] to improve the accuracy? [1] http://mayuresh.sdfeu.org/coinxray.png [2] https://pdf.indiamart.com/impdf/22884448473/MY-16502350/dental-rvg-systems-kodak-5200.pdf
