Histogram luminosity values changed

[bruuuke]

I'm currently recording the median luminosity and standard deviation of luminosity values in various photographs. This has been an ongoing project so I've been working on it for probably the last 4 months. Today I resumed my work and had to go back and check a previous photo that I had already recorded luminosity values for and noticed that the luminosity values that I had originally recorded were different than the values I'm seeing today in the histogram.

The attached picture shows the histogram I'm using (and have been using since I started this project). It is showing a median luminosity and standard deviation of luminosity for a photo that originally gave me this median luminosity value: 75 and this standard deviation: 27.87



I'm wondering if somewhere during this project I accidentally changed some setting in photoshop that affected the luminosity readings, or if the luminosity values of a photo are estimated by photoshop and thus aren't always the same etc. ?

Any help on the issue would be greatly appreciated, thanks!
Brooke

 

[SCTRWD]

According to evenly spaced vertical gaps on your histogram my guess is that some adjustments have been done on your image. Levels? Auto Color?

 

[bruuuke]

Thank you for your input, I realized today that I completely blanked out and was using the RGB histogram and not the actual luminosity histogram!

Sorry for the inconvenience, your reply was the only reason I realized that though because it made me take a better look at the actual graph instead of the numbers.

Silly mistake, but thank you!