Vegetative cover estimates- grid overlay possible?

Posted by sarah Al-beidh on Feb 23, 2011; 9:26am
URL: http://imagej.273.s1.nabble.com/Vegetative-cover-estimates-grid-overlay-possible-tp3685534.html

Hi all,

A few months ago I emailed the list to ask how I could calculate the proportion of vegetation on hundreds of 3mx3m plot photographs.  Your suggestions were to adjust the color threshold and then threshold each image and finally to use a macro to calculate the proportion of white pixels on each thresholded photo.  This worked a treat but it has ended up meaning that by standardising the protocol (ie. hue=32 etc.) I end up underestimating vegetative cover on many of the plots (where vegetation is either pure white or dark brown).

Consequently, we have come up with an alternative idea that would involve overlaying a grid over each photograph and counting the number of filled squares to gain a separate estimate of vegetative cover per plot.  Is there any way of overlaying a grid of a set size on each photo using Image J?

Many thanks,
Sarah

Dr. Sarah Al-Beidh
RHS Wisley