### Author Topic: Under-/Overexposure bar for histogram  (Read 6959 times)

#### KarateBrot

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• Posts: 80
##### Under-/Overexposure bar for histogram
« on: July 20, 2012, 02:21:18 AM »
This is my concept:
In the histogram menu you can enable two bars which will show up on the left and right side of your histogram. The left one will show the percentage of underexposed pixels in your footage and the right one will show the percentage of overexposed pixels in your footage. You can also set a threshold to choose if a pixel is under-/overexposed (like for the zebras).
It might look like this:

I already thought a littlebit about the algorithm to calculate the percentage for a bar. Unfortunately I am not experienced with programming so I can only show you my ideas. But I'd be happy to help out in any way possible if you all find this idea interesting.
As an example I will show you the (mathematical) algorithm for the overexposure bar for one frame (underexp. is analog to this).

- - - - -

The ratio R of overexposed pixels n compared to the full resolution N in the footage that will be displayed in the bar is given by

whereas the resolution N in the footage is given by its width x and height y

To tell if a pixel at position (i,j) is overexposed (greater than a threshold T) or not we now define a function tau which is 1 if the pixel's brightness B(i,j) is greater than T, else 0

Now we look at each pixel and add 1 to the total number of overexposed pixels n if it's overexposed

Now that we can calculate n let's throw it all together to the final formula to display the percentage R of overexposed pixels shown in the bar

In words: Count overexposed pixels line by line and compare it to the overall amount of pixels.
Btw. if it needs too much processing power we could approximate it and only look at the center pixel of a 3x3 or 5x5 area for example. It would only take up about 1/9 or 1/25 processing power this way and would be still very precise.

- - - - -

Negative:
- May need some processing power (maybe, I don't know)

Positive:
- You can see how many percent of the histogram's area is cut off
- Great overview of the amount of under-/overexposed areas
- The underexposure bar can also be an indicator for how much noise you can see in your shot
- You can quickly balance your settings (ISO, Aperture, Exposure, variable ND filter) for a combination of minimal underexposure and overexposure in contrasty shots (optimize dynamic range)

- - - - -

Index:

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##### Re: Under-/Overexposure bar for histogram
« Reply #1 on: July 20, 2012, 02:15:53 PM »
Can't you just use fast zebras + histogram? Fast zebra are cpu-free and show a better overview of what's wrong
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#### a1ex

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##### Re: Under-/Overexposure bar for histogram
« Reply #2 on: July 20, 2012, 02:19:27 PM »
The current dots are displayed when percentage exceeds a given threshold - look in the submenu.

But I think you really need log display for the percentage.

#### KarateBrot

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• Posts: 80
##### Re: Under-/Overexposure bar for histogram
« Reply #3 on: July 20, 2012, 09:36:50 PM »
Can't you just use fast zebras + histogram? Fast zebra are cpu-free and show a better overview of what's wrong
Yeah sure I can also use the zebras and I do use them quite often. They show a very good overview of which areas are wrong but then, still you can just estimate how much of your image is properly exposed. With the additional bars you get let's say a "summary" of your under-, over- and properly exposed spots. This is quite a good, fast and accurate help to decide how to expose in difficult shots with a lot of contrast.

The current dots are displayed when percentage exceeds a given threshold - look in the submenu.

But I think you really need log display for the percentage.
Yes, I know about the dots. They are very helpful, too and I never turn them off. The bars go a step further and tell how far the histogram is pushed out of the limits.

I worked with this kind of bars on a rented Red EPIC-X for the first time and it was such a nice addition to the histogram. It sped up the time I needed to get the right look a lot (even when zebras were active). It is a great way to get an exact balance between under/overexposure and I thought this might be a great addition to ML as well. That's why I made this feature request.

If the workload of programming it bothers you I can try to learn it a bit better and try to program this myself. I just need to know if there might be a chance of including it into the firmware once you get the finished code. I don't want to do a lot of work for it which is already doomed to get abandoned
Is the language used by ML C or C++ ?
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#### a1ex

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##### Re: Under-/Overexposure bar for histogram
« Reply #4 on: July 20, 2012, 09:49:41 PM »
If people like it, why not?

#### scrax

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##### Re: Under-/Overexposure bar for histogram
« Reply #5 on: July 20, 2012, 09:57:20 PM »
I like that feat request, looks like i'll keep it on with the histogram almost always if added
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#### KarateBrot

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##### Re: Under-/Overexposure bar for histogram
« Reply #6 on: July 23, 2012, 08:53:18 PM »
Alright, so I might need some help. Could you tell me where exactly I can find the code for the vectorscope and for the histogram? I want to take a look at how the chroma and luma data is getting detected and processed.
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#### mkrjf

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• Posts: 53
##### Re: Under-/Overexposure bar for histogram
« Reply #7 on: June 30, 2013, 10:12:29 PM »
very nice feature - could even be used instead of histogram redraw
Does not need complex math - jus percentage of pixels all white or all black
Set threshold at some %
open aperture until bar lights up and then back off - could be very intuitive