Magic Wand Tool Histogram Pixel Count

KG
Posted By
Kate_Garland
Jan 16, 2009
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835
Replies
1
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Closed
I am working on a research project that involves evaluating the relative abundance of various colors in a leaf. The leaves that I am working with have three distinct sections of color (green, burgundy, and coral). I have scanned images of the leaf samples on a flat bed scanner (all with the same quality) and am using the magic wand tool to determine the total pixel count of the leaf and the total pixel count for each individual color. With this data, I determine the relative percent of each color within the leaf.

This process works for 80% of my images. The other 20% indicate that the total pixel count of the leaf is less than that of one single color within the leaf. The dotted outline surrounds the leaf just as it does with all of the other images and there isn’t anything else in the image that the wand tool is picking up.

Any thoughts?
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C
Curvemeister
Jan 16, 2009
I would not recommend the magic wand tool for this purpose because it is time consuming and inaccurate.

A better method would be to convert to Lab mode, and use the blend-if sliders – found in Layer Properties – to generate an exact mapping of lightness and hue values.

One possible procedure would add an all white layer, with blend if sliders to select white for the areas you are interested in, with a curves adjustment layer above the white layer: use a steep curve to map all the non-white areas to black.

There will be four numeric values – leaf area (based only on Lightness slider settings, and three hue values, using the same Lightness settings, but different ranges for the a and b channels for the hue values.

This can be made into an action, and would have the advantage of requiring no manual work, other than copying the mean values from the histogram palette.

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