Adobe Photoshop/photoshop question


algae with fish bites
algae with fish bites  
Hi Dan,

I am a researcher and looking for a simple way to figure out a problem. My project is essentially figuring out how much algae is eaten off by fish, so I have many pictures of tiles made up by yellow holes where fish bite from and green parts where algae still remains. I was hoping there was a way on photoshop to get a percentage of the spots that are yellow compared to spots that are green, otherwise just a way to make the two colors more distinct as some photos come out blurry. If you have a solution to my problem, I would forever be in your debt!

Bertrand Shao

Hi Bertrand,

Photoshop will not be able to do the calculations for your percentages. Sorry.

If you can redo the study with a red or pink tile you may have better results. A black or white tile would also be preferable to yellow. The problem is that yellow is right next door to green in the color spectrum, so it will be hard to separate them in this photo.

But if you have to use these shots, you can try the following steps...

From the top menu choose - [Select]-[Color Range]. Fiddle with it until you have the algae selected then fill it with a new color, or better yet put the selection on a new layer (ctrl + J) and apply a Layer Style (Color Fill would work well) to the new layer.

I hope this helps.

If you don't know what a Layer is or a Layer Effect is you should buy a book on Photoshop, or do some serious Googling.

Good luck.


Adobe Photoshop

All Answers

Answers by Expert:

Ask Experts


Dan Loffler


I can help with specific "How To" questions. No Photoshop Elements questions please.


I have been using Photoshop every day in my work as an Art Director and Graphic Artist since 1993 with version 2.5. I am currently employed as a Creative Director in Miami. I have taught computer graphics classes at CompUSA, Computer City. I currently teach a crash course on Photoshop to digital photographers on Digital Photography Corner's Digital Photography Cruises. I have worked as a personal Photoshop tutor for clients as far away as Seoul Korea.

©2017 All rights reserved.