This post is a bit more technical than most of what you'll find on this blog, but I've been facing the predicament of having to estimate the initial vegetation cover in my alfalfa plots and have figured out a way to do it using photoshop. Here's my how to, for anyone who faces a similar task.
If you have suggestions for a better way to estimate the vegetation cover for photos like the one I've used as an example here, I'd love to hear about it. Email me, or add comments below.
If you have suggestions for a better way to estimate the vegetation cover for photos like the one I've used as an example here, I'd love to hear about it. Email me, or add comments below.
Step 1- Take photos looking straight down at vegetation. Import into photoshop. I'm using Photoshop CS4, 11.0.2
Step 2- Remove shadows and highlights. Using the Image--> Adjustments --> Shadows/ Highlights tool and setting both ‘Shadow’ and ‘Highlight’ settings to 100%.
Step 3- Select a color range using the magic wand tool. I set the magic want tool to a tolerance of 10 (selecting the 10 colors above and below the selected pixels) and selected 10 points within the alfalfa around the photo (using additive sampling).
Step 4- Select and refine. Use the Select--> Similar tool to select all greens within the 10 shades above and below the colors selected with the magic wand tool. Then, use the Select-->Refine edge tool to expand the selection. I set the refine to the maximum radius, contrast and smoothing settings, a feather of 8.1px, and an expansion of 32% because alfalfa grows in clumps and the initial selection was only choosing the center of many of the clumps.
Step 5- Select more. Use the quick selection tool to select any areas that the above steps missed.
Step 6- Copy and paste the selected parts of the image into a new layer and turn off the background layer. You should only see the areas that were selected. Use the erase tool to erase any areas that should not be included in the pixel count (for me, these were areas in shadow that were picked up, as well as weeds that I didn't want to count).
Step 6- Copy and paste the selected parts of the image into a new layer and turn off the background layer. You should only see the areas that were selected. Use the erase tool to erase any areas that should not be included in the pixel count (for me, these were areas in shadow that were picked up, as well as weeds that I didn't want to count).
Step 7- Open the histogram box and make sure you're looking at 'Expanded View'. You should see a box below the histogram with data including a pixel count. Toggle between Source: Entire Image (for the pixel count for the original image), and Source: Selected Layer (for the cutout of the selected vegetation). Divide the latter by the former and you'll get the proportion of the original image that was selected in steps 3-6. Add to your spreadsheet and you're done.