Mobile app for pH color comparison

[generessler]

Hi all. People seem to post regularly saying they have trouble comparing colors for the standard pH test. Certainly color blind people must? For me 7.8 and 8.0 look almost the same. Of interest because 8.0 is my trigger to add acid.

It would not be super hard to build an app that uses a phone's camera to do the comparison. I'm not talking about evaluating the color of the test water on its own, rather doing the same comparison you would by eye: Aim the camera at the test vial; the app picks the standard color block closest to the sample.

I was pretty surprised the only thing I could find was a Clorox app that claims to work with their test strips.

I'd consider taking this on as a hobby project (I'm a software engineer by day) if it makes sense and doesn't already exist somewhere.
Thoughts?

 

[JoyfulNoise]

Testing apps that measure test strips using a smartphone cameras have been around a while and are mostly abandoned by the industry. It’s not a very fruitful area of development because there are just too many factors that are outside the apps the control such as ambient lighting, measurement errors and calibration. Not all cell phone cameras are made equally and some render colors very badly. You can certainly try if you want to but I feel it’s mostly a waste of time. If someone really needs help with pH, then decent pH meters can be had for less than $100.

At the end of the day, pH is far less important than it is made out to be by the industry. Once cyanuric acid stabilizer is present, the effect of pH on the ability of chlorine to sanitize is minimal. This is why TFP de-stresses the need for hitting a specific pH target. As long as the pool water pH is between 7.2 and 8.0, it is perfectly safe to swim in. Not being able to differentiate between 7.8 and 8.0 is really no big deal, pH doesn’t change rapidly enough to be of concern. Simply knock the pH down once it registers on the high end.

 

[generessler]

Thanks. I get it. Not an urgent thing.

But technically it ought to work. Just look for the minimum color distance in a perceptually uniform space like CIE. That ought to mostly account for lighting, camera characteristics, etc. If a phone is less than about 4 years old and from a major manufacturer, the camera is certain to do a better job than most humans.

 

[Gary Davis]

It won't work for colorblind people but I keep a plate of white plastic in my test kit so that it's always the "same" white background every time.

 

[SoDel]

Thanks. I get it. Not an urgent thing.

But technically it ought to work. Just look for the minimum color distance in a perceptually uniform space like CIE. That ought to mostly account for lighting, camera characteristics, etc. If a phone is less than about 4 years old and from a major manufacturer, the camera is certain to do a better job than most humans.

Won’t cost you anything to try. I know for myself, I try to differentiate the little bit of “orangeness“ when deciding and interpolating on its way up to 8.0+. For practicality, time to add acid when I can’t see any “orangeness” at all and it’s (at least) 8.0 (and if it’s a day I just don’t feel like adding acid that day, my mind wills a little hint of orange into existence for another day ). Don’t need an app for that lol (but it still sounds like an interesting project / experiment and I hope you’ll update with progress).

Taylor has an app that’s supposed to read its test strips automatically. Haven’t tried it — everyone says a dart board gives better results than test strips and darts are more fun.

 

[JoyfulNoise]

Thanks. I get it. Not an urgent thing.

But technically it ought to work. Just look for the minimum color distance in a perceptually uniform space like CIE. That ought to mostly account for lighting, camera characteristics, etc. If a phone is less than about 4 years old and from a major manufacturer, the camera is certain to do a better job than most humans.

In order for this to work accurately, I believe every pH test will need 3 measurements - 2 color standards at the end points of the x-y line connecting the extremes of phenol red color and then the actual measurement itself. Phenol red is yellow (~570nm) when the pH is below 6.5 and "purple" (~430nm) when the pH is over 8.4. The problems involved will be both wavelength detection (color) as well as saturation relative to the white point. Saturation of the color is controlled by the concentration of phenol red in solution and the transmitted light used. One can easily see this when varying the number of indicator drops. When you add one less or one more drop to the test, the color saturation changes and the perception of that color changes as well. You can also see color changes when the background lighting used for transmission is varied. If I hold my test sample up to a white cloud in the sky, it looks very different than when I hold it to the light tan color of my concrete deck.

Certainly have it if it's a hobby of yours and keep us posted.

 

[dfwnoob]

I had the same idea on here a few months ago. I think it would be easier to do on iOS where you're not solving for 10,000 different cameras and calibrations. In my head, it would involve some sort of special comparator block with it's own built in illumination that could attempt to make the color as standardized as possible, regardless of ambient lighting. You could have a "standard" color set on the block that the software looks at to represent each level, and then compare the actual sample against those predefined colors. But once you get to the point that you're creating custom made comparator blocks with built in LEDs, you may as well just buy a higher end digital pH meter.

My other idea was a more basic app for colorblind testers that could look at the drop tests and tell you when the color stops changing, that seems like it would be easier.