I’ve been learning about photography.  I’m totally unsuccessful from an artistic point of view but I’m finding the mechanical aspects really interesting. Mostly as a result of this amazing free online course (warning, I found the course quite maths heavy, and I did a PhD that focused on maths)

Since I started looking more carefully at photos, I’ve felt like the pictures I put on Instagram looked different there. Light something had changed in the contrast or similar. I wanted to do a quick experiment to find out if it was my eyes playing tricks or indeed some interesting optical illusion.

So I found a handy wikipedia page and took a screenshot of it.

First image date:date

I then converted that screenshot (which was png on a mac) to jpeg so it could be put on Instagram:

Secondimage

It was posted (it’s since been deleted because it’s very uninteresting to my followers) and I took a screenshot of the image on both my phone and on my mac. PS: fairly obviously, I didn’t use a filter or adjust anything)

I lined up all the pictures and took one large screenshot:

Alt text

then used Darktable’s color picking tool to check each colour (using area rather than spot measurement:

Alt text

and it turns out it isn’t an optical trick: the colours do come up differently when tested:

Alt text

The order of samples is:

  1. Screenshot png
  2. Screenshot jpeg
  3. Instagram on desktop
  4. Instagram on phone

and clearly the ones that Instagram does are different from the ones that aren’t.  So what is going on?

  • I don’t think that noise is making a difference (I do think that inprecision in my measurements is causing the tiny differences between the jpeg and png versions).
  • I don’t think it’s the monitor making the difference – the test could have been done entirely without looking at the monitor so that’s out.
  • I don’t think it’s something about firefox – because that wouldn’t explain why the iPhone screenshot is different by the same amount.
  • It’s not a darkroom import artifact – all the colors were on the same image screenshot before darkroom got involved.

This suggests that Instagram really is doing some unnecessary alterations to photos as they go thought the process.