Generally one does have to set the scale on each image if relative size comparisons are of interest.
Dean On Fri, Oct 18, 2024, 5:40 PM 'Chris J Conroy' via Morphmet < [email protected]> wrote: > Hello morphologists, > > I’ve created a landmark dataset for ~250 mammal skulls. My process > was to take images in the same view, with a ruler in the image. I opened > the files in ImageJ and plotted the points. I’ve made an input file in > MorphoJ and done the usual analyses, which largely make phylogeographic > sense. However, centroid size appears to be in semi-discreet bands of > values ranging from near 0 to near 4000. I’m sure the variation comes from > at least two sources. One is that I used two cameras, one at 72 DPI and the > other at 96 DPI. Opening the images in Mac Preview allows me to check this. > Next, in ImageJ, it looks like for some of them I set a scale based on the > image density and others I did not. The landmark XY values themselves > differ by orders of magnitude. > > I took a sample of specimens from top to bottom of the centroid size > variation and fixed the scale in ImageJ and recreated the landmarks. The XY > values are now in the same range. > > Before I sit down and do this for all 250 images, I wanted to see if this > is going to be a waste of time, or will images from different digital > cameras going to be fundamentally different in centroid size and not worth > the work. I suppose I could do the work and then code all the images by > camera and see if there is an obvious effect. Surely I’m not the first > person to go through this. > > If it comes to it, I can re-take the lower res images on the higher > resolution camera. > > Lastly, on the higher resolution camera, some images are slightly zoomed > to fill the image with the object. Will this also mess up centroid size? > > Thanks, > > Chris > > > > -- > You received this message because you are subscribed to the Google Groups > "Morphmet" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > To view this discussion on the web visit > https://groups.google.com/d/msgid/morphmet2/6573acc0-0f88-4d26-9cc5-2c1546d0860dn%40googlegroups.com > <https://groups.google.com/d/msgid/morphmet2/6573acc0-0f88-4d26-9cc5-2c1546d0860dn%40googlegroups.com?utm_medium=email&utm_source=footer> > . > -- You received this message because you are subscribed to the Google Groups "Morphmet" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion on the web visit https://groups.google.com/d/msgid/morphmet2/CAOQKhBPdG2LN8A8okkXuN_KjDY9L34YxFsp3YiCKU1%2Bz_DDuhA%40mail.gmail.com.
