SV305 odd histogram

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brisguy
Posts: 5
Joined: Fri Mar 26, 2021 4:08 am

SV305 odd histogram

Post by brisguy »

Hello,

New Sharpcap User and new SV305 owner.

I am wondering how to interpret the histogram spreadsheet I get when save a camera snapshot. The histogram itself is fairly 'fuzzy', meaning the frequency is varying quite a bit as the values change. Below is an example taken from the spreadsheet, which is the result of a white-balanced capture.

Red Green Blue
12043 13520 05
22424 13633 53
15276 14378 65
22163 14821 02
20061 15369 89
14157 15918 04
23912 16200 83
16265 16527 06

This small segment misses the Blue peak, but clearly shows the issue. The frequency of the Green pixels progresses smoothly, while the Red and Blue pixels show wild swings. Does this indicate an A/D problem? NOTE: I added the zeroes to the Blue column to get the numbers to line up properly.

Thanks, Stan
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admin
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Re: SV305 odd histogram

Post by admin »

Hi Stan,

have you used the colour balance features for the camera to try to get the image to have a natural colour to it? Making adjustments to those controls can lead to the sort of features you're describing in the histogram where there appear to be gaps in the data at some values. If you set the colour balance controls back to their default values then hopefully this should go away. What is happening is that when you set the colour balance to increase the amount of blue in the image by 50%, the camera software multiplies each pixel value for the blue channel by 1.5. That means if you start with pixel values of 1,2,3,4,5 you will get adjusted values of 1, 3, 4 (rounded down from 4.5) 6, 7 and so on.

cheers,

Robin
brisguy
Posts: 5
Joined: Fri Mar 26, 2021 4:08 am

Re: SV305 odd histogram

Post by brisguy »

Yes, this was after using the auto balance adjustment (about 160 for Red and Blue, 100 for Green). I assumed this was the correct way to use the software. Otherwise the image looks bad (green). However, this raises another point. I assumed the histogram showed me the actual pixel values. Is that not the case? If not, how can I use the histogram to determine exposure? Also, does the histogram divide the green frequency numbers by two? Otherwise, I would think those numbers should be higher.

Thanks!
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Re: SV305 odd histogram

Post by admin »

Hi,

you can certainly use the camera controls to adjust the white balance - plenty of people get good results that way, but it can lead to the sort of histogram gremlins that you noticed.

SharpCap 3.2 produces the RAW histogram by debayering the image so the pixel counts work out to be even between the colours. 4.0 can calculate without the debayer, so does show 2x the amount of green pixels.

Robin
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