A720 IS and its overexposure-behaviour - page 4 - General Discussion and Assistance - CHDK Forum
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A720 IS and its overexposure-behaviour

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Offline LjL

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Re: A720 IS and its overexposure-behaviour
« Reply #30 on: 19 / July / 2008, 08:31:16 »
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Aren't you by any chance used to DSLR cameras?

Have a look at this link that was posted in another thread. Look at the curve.

Do you have any other P&S cameras to compare this behavior with?

By the way, both your links point to the same address... I don't think I can see the "roof correct" image (unless it's down in the same JPEG, but I'm on dial-up and can't load the whole thing).

Anyway, the solution should be: underexpose and then boost the curve up, just like the link describes. And just like the link mentions (but more, because this isn't a Fujifilm), do expect noise in the shadows if you do that.
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Offline viewpix

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Re: A720 IS and its overexposure-behaviour
« Reply #31 on: 19 / July / 2008, 08:41:35 »
Unfortunately i mixed up the links, pls review again the two pics. Sorry!

Btw: i am aware of the circumstance that human eyes have a larger dynamic range, but what we see here is a software-problem.

Quote
Do you have any other P&S cameras to compare this behavior with?
Unfortunately my neighboor with his panasonic lumix is not at home, but i did several compares before and the lumix ever did a good job (but theres no CHDK for it  :P)...
« Last Edit: 19 / July / 2008, 08:46:27 by viewpix »
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Offline LjL

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Re: A720 IS and its overexposure-behaviour
« Reply #32 on: 19 / July / 2008, 09:01:12 »
Which Lumix? Some models I've seen samples of on imaging-resource have remarkably good noise behavior (or cunning noise reduction), so they can possibly afford underexposing a little more without the shadows becoming a mess.

I don't know how to write a curve that works with the CHDK curve feature, I haven't tried, but a curve in itself is simply a mapping between input values and output values, so, generally speaking, it can be described by something like this:

0 0
1 1
2 3
3 4
4 6
5 7
6 8
7 9
8 10
9 10

This would be a curve that stretched the shadows a bit and squashes the highlight (kind of the opposite of what you want, I just made numbers up). Of course, a real mapping is not made of 10 values, but rather 1024 if we're talking about 10 bits per pixel.

You probably want a curve much like the second one in the link I gave you.


My two cents: shoot a couple of photos raw (no matter how much you dislike that), then open them in your favorite photo editor and play with curves there.
Find a curve that pleases you (don't just try one picture, though, or you might easily be misled), and only then go on setting it up in CHDK itself.

And beware, anyway: although I haven't tried it, it's very likely that the custom curves feature slows down shooting. It's processing the raw data, and that takes time on the humble ARM chip we have.
« Last Edit: 19 / July / 2008, 09:06:45 by LjL »
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Offline lukg

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Re: A720 IS and its overexposure-behaviour
« Reply #33 on: 19 / July / 2008, 09:26:44 »
The first image is well exposed (except for the roof and the sky but...what was your subject?). Your scene has too much contrast for the camera.
Since the first image is 90% well exposed, what about shooting in RAW and using Photoshop Highlight&Shadow recovery?? (Image --> Adjustments -->Shadow/Highlight (show advanced options)
You would be able to keep all the well exposed area and to work only playing  with the highlights
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Offline viewpix

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Re: A720 IS and its overexposure-behaviour
« Reply #34 on: 19 / July / 2008, 09:57:28 »
@LjL: oh, the curve will only be applied to a RAW and not to jpeg-processing? Well then...look at my comment for lukg

@lukg: imagine coming back from vacancies and then processing hundreds of pics in photoshop? no, no, live is too short for that :-) For the same reason i dont shoot RAW.

Is there anyone who can give me a working example of such a curve? (Only necessary if a curve is applied to jpeg, see my comments above).

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Offline lukg

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Re: A720 IS and its overexposure-behaviour
« Reply #35 on: 19 / July / 2008, 10:08:31 »
Quote from: viewpix on 19 / July / 2008, 09:57:28
@lukg: imagine coming back from vacancies and then processing hundreds of pics in photoshop? no, no, live is too short for that :-) For the same reason i dont shoot RAW.

:) I respect your habits, when I come back from vacancies I cannot wait to develope my raws. I lose my last free day before i come back working to do that only ;)
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Offline viewpix

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Re: A720 IS and its overexposure-behaviour
« Reply #36 on: 19 / July / 2008, 10:16:24 »
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Offline LjL

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Re: A720 IS and its overexposure-behaviour
« Reply #37 on: 19 / July / 2008, 18:30:18 »
viewpix, the curve will be applied to the in-camera raw, which means it will also be applied to the JPEG (you know the JPEG is created from the raw to begin with...).

There's a reason the feature is called "custom JPEG processing"... ;)

As for the working example, for goodness sake, what's wrong with the curve editor that's linked to in the first post of the Collaborative Build thread we gave you at the beginning? I've just downloaded it, it seems an extremely easy curve editor to use to me.

If you want us to make a curve for you using it... well, only you know the result you want, so go and play with it. Try to replicate the curves in the article I gave you and see the results you obtain on sample photos, if you want somewhere to start with.
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Offline RaduP

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Re: A720 IS and its overexposure-behaviour
« Reply #38 on: 19 / July / 2008, 20:22:30 »
Well, as others posted, that's normal for a P&S camera, and there is not much to do about it due to the 10b ADC. You can try to do a HDR though.
Your other (easier) options are to buy a DSLR, or, for the best color range, a film camera ;)
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Offline viewpix

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Re: A720 IS and its overexposure-behaviour
« Reply #39 on: 20 / July / 2008, 05:12:44 »
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