Wednesday, July 22, 2020

Can I trust my phone? Part 2

A while back, I downloaded an app that would do spectrometry. It would split light coming into the camera into its constituent "rainbow", which is cool since that is a way to analyze a substance. Each element has a rainbow fingerprint.

I was excited! I wondered if the representations of incandescent elements on the Internet would be true enough to create a faithful spectrum, so Zi pulled up a picture of a hydrogen lamp and looked at it with the spectrometer. Hydrogen has a very well known spectrum so I knew what it was supposed to look like. 

Wow! It looked great!...except…why was all that blue there? Hydrogen isn't supposed to have that big blue spike at the left end of it's rainbow.

I took my phone outside and looked at the sky through it's camera  Wow! Blue skies smilin' at me...way too blue skies, did I see. I was blue. I dumped the app.

It wasn't the app's fault. Phone cameras are made to produce pretty pictures and bluer skies are prettier. But they're not true blue and science looks for truth.

My son suggested that I use a yellow filter to remove some of the blue coming into the camera and then use the color balance on the camera to get back to true color, and it worked! On the hydrogen spectrum, it worked, but on everything else, it removed so much blue that I couldn't put any back in. blue again!

But recently I bought a packet of Selens Flight Flash Color Strobist Lighting Gel filters. Gels are plastic films. Less expensive than glass photographic filters, they're often used as compensation filters for different light sources. Slipping the ¼ CTO 6500 to 4500 K lightly yellow correction filter over the camera lens, between the phone and it's case did a great job. I used the SnailCamera Pro app, which gives me considerable color balance control to rebalance the picture and I "eyeballed" it until it looked right.

Here's what the camera saw without the picture.

Here's what the scene actually looked like.

Okay, a caveat. The colors were right but I lost some detail. The individual stones in the chimney lost some definition, but right now I'm more concerned with color values. I think some contrast adjustment could get some, if not all, of the definition back.

But I am impressed with the light capturing abilities of modern cell phones. Here are some early evening pictures I took.

A nice sunset

The same shot after the sun had gone away.

A star. Vega. I could not have seen that with my last cellphone camera.

Cell phones offer a lot of power to record your world but know your instrument. It's primary purposes are communication and entertainment. Accurate records require some finagling.

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