Filming HD from the center of the sensor (Like the Canon 600D) - Feature Requests - CHDK Forum
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Filming HD from the center of the sensor (Like the Canon 600D)

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Offline thunderstorm

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Filming HD from the center of the sensor (Like the Canon 600D)
« on: 06 / March / 2013, 16:43:34 »
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Hello,
On my 600D (A DSLR) there is an amazing native feature, which is unknown why it doesn't exist on the legend 5D Mark II and III:
I can film Full-HD video from the center of the sensor instead of the normal way by grabing every 3rd/4th line. (since only 1080 lines are needed)
The camera actually records a central portion of the sensor - sized 1920x1080, where every pixel on the video is an actual pixel on the sensor. (no every third pixel and so on)
The result is cropping and magnification of the footage: The benefits of that are extra zoom reach (in my 600D with it's 18MP it means close to 3x more zoom) WITHOUT loss of quality and 3 times higher DOF.
Will it be possible to do so on powershots? For example on my Canon SX40: With it's 12MP I assume the magnification factor will be around 2.

You can read about that amazing feature of the 600D here:
http://www.cameralabs.com/reviews/Canon_EOS_600D_Rebel_T3i/movie_mode.shtml
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Offline waterwingz

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Re: Filming HD from the center of the sensor (Like the Canon 600D)
« Reply #1 on: 06 / March / 2013, 16:53:16 »
Doing something like that would require hacking the DSP chip in the camera - something we know almost nothing about.    CHDK works with the Digics processor part of the camera - a fairly slow processor without the ability to do what you've described.
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Offline Davo

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Re: Filming HD from the center of the sensor (Like the Canon 600D)
« Reply #2 on: 07 / March / 2013, 10:06:24 »
This would be a great feature for lunar and solar astronomy so I decided to have a play with my A810. I used this page to find out what PropCases changed when I switched video from 640x480x30 to 1280x720x25.

http://chdk.wikia.com/wiki/PropertyCaseDump

It showed that PropCases 168 and 171 changed from 0,2 to 1,4.

I then used the script below to change these PropCases and tried recording video. I did in fact find a new video mode at 0,1 but it was only 320x240x30. I checked a lot of other values but they either crashed the camera or recorded the stock modes. Maybe Canon have hidden the 600D HD mode in one of these pairings?

Code: [Select]
--[[ @title PropCases
@param a Property (168)
@default a 0
@param b Property (171)
@default b 2
--]]

print("168 = " .. get_prop(168))
print("171 = " .. get_prop(171))
set_prop(168, a)
set_prop(171, b)
print("168 = " .. get_prop(168))
print("171 = " .. get_prop(171))
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Offline srsa_4c

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Re: Filming HD from the center of the sensor (Like the Canon 600D)
« Reply #3 on: 07 / March / 2013, 11:25:15 »
Reprogramming the sensor readout would be great. However,

- nobody succeeded in doing it
- the sensor- and readout related parts of the firmware are very hard to follow or understand
- don't expect crop HD video on a camera with CCD (like the A810), the sensor only supports a few readout modes, and this kind of crop mode is certainly not one of them (low light mode is closer, but the theoretically achievable framerate is not high enough for video)
- some CMOS sensors allow reading reading only a part of the sensor
- even if somebody would find out how to do it, large parts of the firmware are not aware of "other" resolutions or refresh rates, and would probably crash
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