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Spot meter

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Offline pigeonhill

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Spot meter
« on: 06 / February / 2013, 15:14:19 »
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If I use my handheld spot meter I know I am metering through a 1 degree field of view.

In my cameras a spot meter is much wider than this and varies with each camera.

I wondered if it would be possible for CHDK to have a means of metering the centre spot of the sensor at a given angular value, eg 1 degree.

This would help those of use that use zone metering.
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Offline lapser

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Re: Spot meter
« Reply #1 on: 06 / February / 2013, 16:09:38 »
Quote from: pigeonhill on 06 / February / 2013, 15:14:19
If I use my handheld spot meter I know I am metering through a 1 degree field of view.

In my cameras a spot meter is much wider than this and varies with each camera.

I wondered if it would be possible for CHDK to have a means of metering the centre spot of the sensor at a given angular value, eg 1 degree.
I can do that after the shot and return a Bv for any specified area of the picture. You can then use this value to take another shot.

Pre-shot metering isn't available yet. There's a pre_shot live histogram available, but that uses the full picture area. It might be possible to turn the pre-shot histogram into a Bv value. I'm not sure how accurate it would be, or how hard it would be to program.

But if you're willing to throw away one shot, and use the 2nd one, I should have something ready soon.
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Offline Microfunguy

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Re: Spot meter
« Reply #2 on: 07 / February / 2013, 05:57:23 »
Quote from: pigeonhill on 06 / February / 2013, 15:14:19
I wondered if it would be possible for CHDK to have a means of metering the centre spot of the sensor at a given angular value, eg 1 degree.

SDM already supports a spotmeter :-

uBasic command readYUV reads the luminance and UV chroma values from a 24 x 16 pixel area at the centre of the screen.

See 'readYUV' here http://stereo.jpn.org/eng/sdm/ubasic.htm .
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Offline waterwingz

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Re: Spot meter
« Reply #3 on: 16 / August / 2013, 23:36:30 »
Quote from: Microfunguy on 07 / February / 2013, 05:57:23
uBasic command readYUV reads the luminance and UV chroma values from a 24 x 16 pixel area at the centre of the screen.
See 'readYUV' here http://stereo.jpn.org/eng/sdm/ubasic.htm .
follow-up here :  http://chdk.setepontos.com/index.php?topic=8997.msg104158#msg104158
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