Where does 14400 come from, and why doesn't it change?

pigeonhill

1164

« on: 11 / May / 2022, 02:57:11 »

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@reyalp

In playing around with get_live_histo() I've noticed, and am confused, by the the fact that the returned total count is always 14400, no matter what the exposure, ie highly under or over.

I've looked at the histogram.c source and I just don't get it.

Can you throw any light on the 'CHDK constant' ;-)

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reyalp

14118

Re: Where does 14400 come from, and why doesn't it change?

« Reply #1 on: 11 / May / 2022, 03:00:20 »

Quote from: pigeonhill on 11 / May / 2022, 02:57:11

@reyalp

In playing around with get_live_histo() I've noticed, and am confused, by the the fact that the returned total count is always 14400, no matter what the exposure, ie highly under or over.

That's the total number of pixels sampled, so it should only change if the viewport dimensions are changed. It's returned so you can convert bins to percent without adding them all up yourself first.

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Don't forget what the H stands for.

pigeonhill

1164

Re: Where does 14400 come from, and why doesn't it change?

« Reply #2 on: 11 / May / 2022, 03:04:20 »

OK.

But on a camera specific basis, why would the viewport change? Aspect ratio change, maybe?

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reyalp

14118

Re: Where does 14400 come from, and why doesn't it change?

« Reply #3 on: 11 / May / 2022, 03:24:56 »

Quote from: pigeonhill on 11 / May / 2022, 03:04:20

But on a camera specific basis, why would the viewport change? Aspect ratio change, maybe?

Yes, aspect ratio is one reason. Can also vary by display device (LCD/EVF/HDMI/analog video), shooting mode (video vs still, some special scene modes), digital zoom...

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Don't forget what the H stands for.

pigeonhill

1164

Re: Where does 14400 come from, and why doesn't it change?

« Reply #4 on: 11 / May / 2022, 03:29:42 »

Just checked the EVF, which reports 14706, as opposed to the LCD 14400.
Thanks for the insight.

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