Exposure adjustment during continuous (burst) mode shooting - Feature Requests - CHDK Forum

Exposure adjustment during continuous (burst) mode shooting

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Offline fudgey

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I'm often shooting in continuous mode hoping to get one good shot of for example a bird flying. Now, since the animal moves, the exposure of the first shot will often be bad for shots taken later, usually due to the position of the sun.

The only way I know of to correct this is to release the shutter and start shooting again, but this will obviously make me miss the best shots.

CHDK is already able to change exposure during continuous mode (bracketing in continuous mode works like a charm), so I figured it could be possible to implement manual Ev adjustment (preferably with configurable step sizes similar to the bracketing feature) using the keyboard left and right keys without interrupting the burst (and why not during custom timer mode as well).

As to which parameter the adjustment should touch...I'd suggest defaulting to Tv since a change in Av may screw up focus (if it's not infinite like it often is). Or, I suppose Av could be up&down and Tv right&left?

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Offline Jucifer

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Re: Exposure adjustment during continuous (burst) mode shooting
« Reply #1 on: 29 / June / 2008, 04:57:42 »
Hmm.

Or could e.g. fbonomi's shot histogram data be used to automagically adjust the exposure?

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Offline fudgey

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Re: Exposure adjustment during continuous (burst) mode shooting
« Reply #2 on: 29 / June / 2008, 05:16:03 »
Or could e.g. fbonomi's shot histogram data be used to automagically adjust the exposure?

Ah yes, forgot to add that note... automatic exposure would be very handy as well, for example if we could enable autoexposure during burst mode by pressing FUNC/SET during the burst (I think turning the feature on/off during the burst is quite essential since a lot of my shooting like this is in "panic mode" with no time to set the camera up, but usually I don't want exposure to change during a burst).

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Offline cyril42e

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Re: Exposure adjustment during continuous (burst) mode shooting
« Reply #3 on: 29 / June / 2008, 05:31:51 »
Or could e.g. fbonomi's shot histogram data be used to automagically adjust the exposure?

I did automatic Tv computation in a script using Canon's Bv value and APEX formula: tv = bv + sv - av (- ev)
It gives results very similar to Canon's computation (except that it can be greater than 1", that's why I did that ;)).
So there is just to replace bracketing formula by this one (if bv is updated between continuous shots)

I also saw ExpCtrlTool_StartContiAE and ExpCtrlTool_StopContiAE Canon's function added in the latest changesets for A series, maybe this could be used too.


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Offline Jucifer

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Re: Exposure adjustment during continuous (burst) mode shooting
« Reply #4 on: 29 / June / 2008, 14:13:54 »
I did automatic Tv computation in a script using Canon's Bv value and APEX formula: tv = bv + sv - av (- ev)
It gives results very similar to Canon's computation (except that it can be greater than 1", that's why I did that ;)).
So there is just to replace bracketing formula by this one (if bv is updated between continuous shots)

Indeed. Let's do that.
If possible.

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Offline cyril42e

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Re: Exposure adjustment during continuous (burst) mode shooting
« Reply #5 on: 30 / June / 2008, 12:04:13 »
Bad news: bv96 (propcase) is not updated in continuous mode (without metering). Maybe it is possible to trigger metering, but I didn't find an obvious solution.

It is probably more simple to use the histogram as Jucipher suggested, but there may be one shot delay (I suppose we will read the reviewed image in the viewport buffer, so we will see that exposure is bad and try to correct for the next shot). It's better than nothing though. However I don't know exactly how to "seriously" adjust tv from the histogram...

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Offline fudgey

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Re: Exposure adjustment during continuous (burst) mode shooting
« Reply #6 on: 03 / December / 2009, 15:24:44 »
Hi all, bumping an ancient thread here but it was mine anyway. :D  Attached is a small patch that implements exposure time (Tv) adjustment during continuous mode (burst) shooting.

There is no menu option for this now, the patch just enables it for good.

It works this way: Set camera in continous shooting mode and shoot. Like always in continuous mode, do not release the shutter. Press the left (or right) key and hold it. Each photo will now be 1/3 stop darker (or brigher). Release the left (or right) key and Tv will remain at the value you've just adjusted.

This patch polls the keyboard only once between shots, between CHDK RAW output and Canon JPEG output (no, you don't have to enable RAW nor DNG output for this patch to work). That's when the key must be in a pressed down state. This patch adds a blue led blink to indicate a successfull adjustment, but its really just for debug and I'd like to remove that (because it slightly slows down the burst and because you can't tell if from the RAW saving LED blink if you have RAW or DNG enabled...although RAW during a burst doesn't make much sense because of speed issues...and at least a570 50ms is already very clearly visible so the blink could be shortened).

If some camera
  - does not have a continuous shooting mode engaged by selecting the mode and keeping the shutter depressed while shooting,
  - or lacks KEY_LEFT or KEY_RIGHT,
  - or has a conflicting built-in or CHDK shortcut key combination that operates during shooting while shutter is fully pressed
this patch may not work.

I gave it a quick test run:

- Appears to work fine on my a570 in normal continuous mode shooting in both P and Tv modes (automatic and manual exposure time modes).
- It also works if CHDK Tv override is enabled (CHDK override works, left/right keys do adjust Tv by 1/3 Ev from the overridden value).
- If continuous mode Tv bracketing is enabled, exposure is not affected by this patch (the debug led still does blink however -- this is a tiny bug that is easy to deal with if the LED blink is a desired feature).
- Maybe there should be a key (SET?) to reset exposure to whatever it was before the user started to adjust it? This would complicate the code a bit and it wastes a shortcut key that might have better uses later so I didn't do that.
- If people like this it can be added autobuilds, but I suppose I'd have to add a menu option to enable/disable it and to select an Ev step (it's now 1/3 stop but I can think of reasons to wish for much bigger steps).


 

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