Filtering Out All colors except a specific shade of red for detection

Hello, and happy 4th of July!

I am currently working on my first Arduino project, and I am trying to automate a computer process. My machine will test for a specific "shade of red" on my monitor. So, I bought a lot of color filters (translucently colored plastic) and photo-resistors. I was planning on simply using the red filter (filters out all color that isn't red) and testing for specific values coming from the photo-resistors, which will be placed on various parts of my monitor. The first problem that I have come across is that the white portions of the screen pass through the filter and appear a greater value than actual red portions do (which I have discovered is because white uses red green and blue). So- how can I filter out all colors, including white, that are not truly red.

Just code to ignore those high values?

You're going to have the same problem with any colour which is a combination of red and one or more others, e.g.purple. To be sure that it is only red, you would have to detect the red, green and blue components of an area (or pixel) and make sure that the blue and green are absent.
I don't think your current method is going to work.

Pete

You will soon discover that even black has red in it. Go buy some black house paint and they add red pigment to the paint.

Paul

You need something like this http://www.robotshop.com/uk/tcs3200-color-sensor.html?gclid=CKvX8vHE8dQCFQ4TGwodBMcB_Q and remove those LEDs.

All the pixels on your monitor will be emitting Varying amounts of Red, Green and Blue. If you are attaching a sensor to a particular area of your screen do you know all the colours/patterns that might be displayed there and will the signals they produce be significantly different from that made by the red shade you wish to detect? If not you are going to have a hard time.

This seems like an odd thing to want to do. You say you are "trying to automate a computer process". Maybe it would be best if you gave more details of that process and what you are trying to achieve.