Fast low-resolution burst/continuous mode - Feature Requests - CHDK Forum
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Fast low-resolution burst/continuous mode

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Offline LjL

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Fast low-resolution burst/continuous mode
« on: 06 / July / 2008, 13:58:00 »
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I know of cameras that have a "normal" burst shoot mode with speeds similar to the Canons, and another "fast" mode that, by limiting the resolution to 2 megapixels or so, manages to shoot much faster (3-4 frames per second).

Nikons have something similar (though slightly different), too: they take 16 shots and fit them all in the size of a normal frame. This one is perhaps a bit too far-fetched.

This would be very nice to have on my A720... 1600x1200 (2 megapixel) is the resolution at which I can use things like PhotoAcute at a practical speed, and if such resolution would allow me to shoot at several frames per second, it would open possibilities for easy hand-held HDR/DOF/etc braketing!
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Offline fudgey

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Re: Fast low-resolution burst/continuous mode
« Reply #1 on: 06 / July / 2008, 14:32:33 »
The technical problem here might be that these cameras always shoot a full resolution RAW image (except in video mode) and then scale it down according to the user's wishes. So I believe for this we would have to replace Canon's shooting functions and communicate with the sensor ourselves. And after that we'd probably have to communicate with the JPEG codec as well (saving those RAWs would be too slow to keep up with the speed). I believe we don't quite know how to do either.
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Offline LjL

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Re: Fast low-resolution burst/continuous mode
« Reply #2 on: 06 / July / 2008, 15:31:52 »
Well, we know how to "develop" a RAW into JPEG tricking the codec into thinking the RAW is actually sensor data, don't we?
With that knowledge, we could feed the codec 4 tiled shots in the same RAW (assuming each shot is half the normal resolution of a RAW).

We'd have to communicate with the sensor ourselves, that's for sure... in fact, this feature request was prompted by my questions about reading sensor data.


By the way, the fact that the camera always shoots full-resolution isn't surprising by itself, since that lets the camera interpolate down, while if if directly read less sensor data, no interpolation would take place, and aliasing would occur with subjects very well in focus.
This would be a drawback, but hey, that's what image stacking software is for... well, no, it isn't there to fix aliasing, but anyway.
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Offline dzsemx

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Re: Fast low-resolution burst/continuous mode
« Reply #3 on: 07 / July / 2008, 02:46:46 »
Quote from: fudgey on 06 / July / 2008, 14:32:33
The technical problem here might be that these cameras always shoot a full resolution RAW image (except in video mode) and then scale it down according to the user's wishes. So I believe for this we would have to replace Canon's shooting functions and communicate with the sensor ourselves. And after that we'd probably have to communicate with the JPEG codec as well (saving those RAWs would be too slow to keep up with the speed). I believe we don't quite know how to do either.
just a an existing example:
on a650 i have an iso 3200 scene mode and it uses 1600*1200 resolution and it's faster, around 3-4 fps.
image quality is terrible:(
it works probably with live preview sensor mode
« Last Edit: 07 / July / 2008, 02:50:00 by dzsemx »
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Offline LjL

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Re: Fast low-resolution burst/continuous mode
« Reply #4 on: 07 / July / 2008, 07:35:16 »
Nah, it works with one quarter the full sensor data, most likely... the fact that it's terrible being simply because you can't expect anything good from a 3200 ISO amplification on a small sensor camera.

But it sounds like precisely what I want, minus the 3200 ISO amplification (although if it could be made to work but at high ISO only, I won't complain very much, since my main intended usage is with image stacking software, where noise doesn't matter incredibly much).
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Offline fudgey

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Re: Fast low-resolution burst/continuous mode
« Reply #5 on: 07 / July / 2008, 14:11:57 »
What dzsemx said also means that a650 firmware could be something worth studying first if one would like to do this for other models...

And, it could be that for a650 (and other models which possibly have a similar feature, are there any?), the iso3200 amplification could possibly be removed to make the fast low-res burst available at slightly lower noise as well.
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Offline LjL

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Re: Fast low-resolution burst/continuous mode
« Reply #6 on: 07 / July / 2008, 15:10:13 »
Keep in mind that on the A720, "ISO 1600" is done by just changing the pixel values, not by giving the amplifier more gain (contrary to all the other ISO levels). This might be the case for ISO 3200 on the A650, too, possibly...
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Offline fudgey

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Re: Fast low-resolution burst/continuous mode
« Reply #7 on: 07 / July / 2008, 15:59:28 »
yes of course, by overriding amplification I ment software too obviously. I believe none of these ISO 1600 (let alone ISO 3200) capable models really go beyond ISO 800 in hardware.
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Offline LjL

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Re: Fast low-resolution burst/continuous mode
« Reply #8 on: 07 / July / 2008, 16:28:03 »
Some of the G series (G3, G2...) feature a "high-speed continuous" mode, but since quality isn't mentioned, I suppose that's not achieved the way we're talking about.

The article about the G2 states that fewer continuous shots can be taken in the high-speed mode, which makes me suspect it's simply postponing the RAW to JPEG processing... but then, the G3 articles talks about 14 shots for all mode.

Then again, the A series have "no internal memory" as far as I'm aware, so there isn't a limit to the number of pictures you can take in continuous mode, to begin with, as it's saving to the SD card in real time - kind of a different beast, I guess.
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Offline LjL

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Re: Fast low-resolution burst/continuous mode
« Reply #9 on: 07 / July / 2008, 16:41:19 »
Uhm, for what is worth... on my A720, if I set the "digital teleconverter" on, and keep a resolution of 1600x1200 or lower, burst mode becomes faster: some 1.5 fps rather than the usual 1.3 or so. Not a huge difference, although you can definitely hear the shutter going off faster.

No big surprise, I guess: it doesn't need to read the whole sensor data, and if 1600x1200 is set, it doesn't even really need to interpolate.
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