its been 40years since i studied/played electronics. it just works 😁 and i calibrate the meter without any mathematics ,pretty much the same as my photography.
June 16, 2023
577
-
-
Current implementations use the JPEG EVF image, not much use for determining clipping with all the processing applied. I want blinkies based on the raw data.
-
have you actually tested your histogram accuracy ? because my sony a74 coudnt be any more accurate.
-
"I determined it using the exposure triangle."
Gold 😁
-
It's a histogram of a JPEG, and it's accurately histograms that JPEG :))
-
Scenes don't have brightness, they have a range of brightnesses. Otherwise they are as emotionally engaging as uniformly lit grey cards are.
-
Blinkies based on the raw data would be pretty cool, Glenn.
That would be interesting to do, Donald, but sadly I don't know how to test the accuracy of my histogram.
As you likely know, a histogram is a set of vertical columns arranged sid-by-side, each column width (or "bin") representing a range of values and each column height representing a count of how many image pixel values are within that range. The problem with my histogram is that it is quite small on the LCD and the bin size/width is not given in the manual and, worse, the column heights are auto-ranged to fit the histogram rectangle height and there is no scale shown on the Y-axis of the histogram diagram. So, for me, it is impossible to check accuracy because I don't know the bin width and I don't know the count for any particular bin.
Would you share how you tested the accuracy of the Sony a74 histogram?
-
[deleted]
-
theres a thread i started with 1000 posts somewhere on this forum. are raw histograms important or something like that. good luck finding it.
found it
dprevived.com/t/raw-histogram-and-why-does-it-matter/1848/ -
To prove a fact, one post is usually enough.
A histogram of a JPEG is an accurate (within histogram window width and height constraints) histogram of a JPEG. Ta-daaaa! -
I don't know exactly what the Elephant-in-the-room uses but one standard says "When encoding Y’CBCR video, BT.709 creates gamma-encoded luma (Y’) using matrix coefficients 0.2126, 0.7152, and 0.0722"
en.wikipedia.org/wiki/Rec._709
So Luma would be 100% when 0.2126R+ 0.7152G+0.0722B=1.
-
Thanks - I see that you use RawDigger, this is your posted image:
Because the histogram can be scaled at least you can determine counts and bin sizes.
-
all the posted raw file links wont work as i have deleted the images they were clogging up mu one drive.
any you will get the idea or maybe not its such a merry go round thread with a lot of off topic comments. -
understood
-
In a CIE-referenced RGB color space, luminance is the weighted sum of linearized representations of the three color planes. The weights depend on the color space.
-
[deleted]
-
I'm not worried about a histogram's accuracy, the code to collect the buckets is quite trivial. I'm more worried about the source data used to calculate it.
Okay, a little illustration. Here's a screenshot of an image developed to just past demosaic, still in the linear energy relationship of the raw file:
Pretty easy to follow, the processing toolchain is in the top-left pane, and the result of the checked tool is what is displayed and histogrammed. This histogram is a "linear-linear' depiction (sorry, Iliah...) , and at this point it's distribution is equivalent to the original raw data. Of particular note, the magenta blob in about the middle of the image are blown pixels (the white balance skew made them magenta), but note there's no spike or other indication of that clipping at the right hand side of the histogram.
Now, here's a screenshot of the developed image with the last tool checked:
This is set up to show the histogram you'd see of the JPEG image; to do this, I had to change out my display profile to a linear one and add the 2.2 gamma normally applied by my display profile to the end of the toolchain. Looks more like a "normal" histogram, no? Notice, still no "pile-up" at the top end,
What I want in the viewfinder is for that magenta area to blink. Then, I can say, 'oh, headlight, I can let that go a bit", and increase my exposure a bit. I mean, I had a bit of room to do just that, 1/750sec with ISO gain of 560, do not remember why I had that setting.
-
I very much doubt that.
