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Canon vs CHDK histograms

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Offline pigeonhill

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Re: Canon vs CHDK histograms
« Reply #10 on: 10 / May / 2021, 01:56:40 »
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@reylap

FWIW I've just looked at the M3 histogram behaviour again. The thing I notice is the pulsating way the histogram changes, ie about every second or sub-sec.

Thus, on a static scene, with Canon peaking on or off, the red channel, in particular, jumps between two values. It is clearly visible on the video I just posted.

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Offline reyalp

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Re: Canon vs CHDK histograms
« Reply #11 on: 10 / May / 2021, 01:57:58 »
Quote from: pigeonhill on 10 / May / 2021, 01:03:34
Thanks for confirming the weirdness, I was worried about flagging what I was seeing, as no one else has and the histogram has been with CHDK for so long.
Thanks for flagging it. The histogram has in in CHDK for a long time, but both the CHDK code and camera display characteristics have changed over time.

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The immediate user palliative is to not use the CHDK histogram on the M3, and maybe other cameras?
If the Canon histogram works better, yes. Most CHDK supported cameras don't have a live histogram in the Canon firmware. In a lot of cases, the CHDK one should still give you a pretty good indication, although the over/under warning dots are probably broken for digic 6.

Do you see the erroneous over / under exposure indicator all the time? Based on the things I've discovered, I'd expect 3:2 on the camera screen (not EVF or HDMI out) to look like my G7X shots.

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As for a ‘solution/fix’, I guess that is going to need someone with time and knowledge of the C code in the histogram module.
Yes, the code that samples the display needs to be re-written in a way than handles arbitrary resolutions, and the warning levels need to reflect the real range of values on digic 6.
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Offline reyalp

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Re: Canon vs CHDK histograms
« Reply #12 on: 10 / May / 2021, 02:03:14 »
Quote from: pigeonhill on 10 / May / 2021, 01:56:40
FWIW I've just looked at the M3 histogram behaviour again. The thing I notice is the pulsating way the histogram changes, ie about every second or sub-sec.
Posted where?

I saw pulsing behavior on g7x when the aspect ratio is set to 4:3, probably caused by sampling outside the image data or the wrong offset in YUV tuples.
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Offline pigeonhill

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Re: Canon vs CHDK histograms
« Reply #13 on: 10 / May / 2021, 02:35:20 »
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Offline reyalp

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Re: Canon vs CHDK histograms
« Reply #14 on: 10 / May / 2021, 02:52:02 »
Quote from: pigeonhill on 10 / May / 2021, 02:35:20
https://photography.grayheron.net/2021/05/exciting-things-happening-in-chdk.html
Do you see the same behavior using the camera screen, rather than HDMI out?

As I mentioned earlier, I think it should mostly work (except the warning dots) on the native screen (not EVF or HDMI) at 3:2 aspect. If it doesn't, there may be additional problems specific to the M3 port.
« Last Edit: 10 / May / 2021, 03:00:55 by reyalp »
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Offline pigeonhill

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Re: Canon vs CHDK histograms
« Reply #15 on: 10 / May / 2021, 03:15:15 »
@reyalp

Yes, problem is there in non HDMI mode, ie normal camera mode.

From what I’m seeing, I’m afraid this will/may need a deeper look, eg LCD vs EVF use, Canon format changes, plus the under/over etc

For now, as I say, I’ll just use the Canon histogram.
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Offline reyalp

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Re: Canon vs CHDK histograms
« Reply #16 on: 10 / May / 2021, 03:23:29 »
Quote from: pigeonhill on 10 / May / 2021, 03:15:15
From what I’m seeing, I’m afraid this will/may need a deeper look, eg LCD vs EVF use, Canon format changes, plus the under/over etc
As I said before, I would expect the EVF to be broken.

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For now, as I say, I’ll just use the Canon histogram.
I would like to understand the problem so it can be fixed. Based on what I've found so far, I would expect your camera to behave like G7X if you are using the LCD display, and the image aspect ratio is such that it uses the full screen width.

If this isn't the case, I'd like to know.
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Offline Ant

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Re: Canon vs CHDK histograms
« Reply #17 on: 10 / May / 2021, 03:28:13 »
Probably this problem is caused by incorrect viewport buffer dimensions. Have you tried earlier builds?
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Offline pigeonhill

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Re: Canon vs CHDK histograms
« Reply #18 on: 10 / May / 2021, 03:42:43 »
@reyalp

Just looking at 3:2 format, I would say the CHDK histogram is about 1-2 stops different to the Canon.

For example, a histo peak on the Canon at -3eV from highlights, will be at about -1eV on CHDK.

Update

The difference scales as you shift exposure.
« Last Edit: 10 / May / 2021, 06:02:58 by pigeonhill »
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Offline pigeonhill

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Re: Canon vs CHDK histograms
« Reply #19 on: 10 / May / 2021, 03:53:26 »
Screen grab
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