Fast low-resolution burst/continuous mode

[LjL]

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!

[fudgey]

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.

[LjL]

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.

[dzsemx]

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

[LjL]

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).

[fudgey]

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.

[LjL]

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...

[fudgey]

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.

[LjL]

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.

[LjL]

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.

[cyril42e]

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.

Yes, the digital teleconverter speeds continuous mode up from 1.5fps to 2fps on sd1000 (digital 1.9x, 1600x1200).

But no noticeable difference between 7MP super fine (~3MB files) and 2MP normal (~300KB files), always 1.5fps. That's strange because writing 3MB on the SD card at 20MB/s takes ~0.15s, which is the difference between 1.5fps and 2fps (0.65s to 0.5s), withnotstanding jpeg processing which should be faster too. So why isn't there any change in speed ?

[dzsemx]

just a notice:
on a650 iso3200 scene mode uses preview / live view data for taking picture
i can't shoot normal raw in this mode, i can't see too much valid data in this mode
seee image
made with raw develop using normal auto mode
and  i didn't notice speedup when using teleconverter

[cyril42e]

on a650 iso3200 scene mode uses preview / live view data for taking picture

How can you get 1600x1200 resolution with live view?

I think the viewport resolution is lower than VGA, and video mode is VGA at 30fps...

and  i didn't notice speedup when using teleconverter

did you reduce resolution to 1600x1200 too?

[fudgey]

Oh, nice find. Indeed, on a570is too the digital teleconverter speeds things up. When Tv or NR from high ISO doesn't slow shooting down, I get 2.0 fps at 1,9x digizoom (equals to 1600 pix width source image as seen from property #92) and 1600x1200 output jpg.

640x480 seems work at the same or almost the same speed even though the camera has to scale down the image(?). Scaling up to 2048x1536 slows it down significantly.

Digital tele 1,5x gives 2048 pixels wide source image, shooting to 2048x1536 from it gives a burst rate of 1.9 fps.
Shooting to 1600x1200 is slower, about 1.8 fps. This must be due to scaling... scaling the smaller 1600x1200 to 640x480 is so much faster that I couldn't measure it on this quick test.

Without digital tele I got 1.6 fps at full 3072x2304 resolution and 1,55 fps at 1600x1200.

I shot superfine quality to a Sandisk Ultra II 1G card, no RAW obviously, in M mode at Tv=1/1000s and ISO80.

(I measured the time it took for 50 shots for these figures, not very accurately)