[leadguitarest]

Here is a very very low light video I shot with a K7 I filmed through a light with a 50mm lens and 28 mm lens.. I would just point and lock the exposure so it gets kinda grainy at times but not bad at all.. I was kinda going for that look anyway...

You Tube

You Tube

[justruppert]

Hi there

this is just something that crossed my mind this morning, but not having the competences to develop this myself I just wanted to throw it out in the hopes that somebody with the required competences picks it up and does something with it (unless of course my idea is completely non sensical)

Since DSLR video is currently only able to use a fraction of the actual resolution of the sensor to record moving images, wouldn't it be possible to use this limitation and turn it into an advantage by creating something like a stochastic readout of the sensor to avoid moiré patterns (rather than blurring the image with mechanical means like the Caprock and such).

The basic idea would be instead of reading out for instance every third line of the sensor to read out the same amount of information, but in a less regular, more random pattern, possibly even changing the readout pattern between every frame.
I obviously have no idea how complicated it would be to implement such a feature, but if I look at the effort put into the development of compressing video into ever smaller data sizes I can't help but think, that it might just be a matter of shifting priorities.

Anyway, just a thought, not sure what it's worth

Then of course, before getting there it might already be nice to have a 25fps option for those K-7 users residing in Europe hoping to record video under artificial light and maybe even a way to control shutter speed and ISO directly, but that is a whole other matter of priorities I guess...

Best

[falconeye]

Since DSLR video is currently only able to use a fraction of the actual resolution of the sensor to record moving images, wouldn't it be possible to use this limitation and turn it into an advantage by creating something like a stochastic readout of the sensor to avoid moiré patterns (rather than blurring the image with mechanical means like the Caprock and such).

Best, this is a very interesting and innovative idea. It reminds me of Floyd–Steinberg dithering.

IMHO, it wouldn't work though. Two reasons:

1. The stochastic subsampling pattern would transform the moiré pattern into strong noise, more specifically, strong color noise. While it may still look better on a still frame, it will look like strong flicker in a video (with a changing subsampling pattern). Even with constant subsampling, the video will typically flicker as it does with moiré patterns (because even on a tripod, the frames shift by a few µm -- you can see this in my video two posts up).

BTW, one can easily check this out with a random texture (and the current regular subsampling pattern): a random texture like grass or sand. It looks ugly because of strong flickering color noise. This has been criticised by many users of entry-level dSLR cameras (including the K-x) without identifying the cause of texture noise. The K-7 has fewer problems because of its more fine grain subsampling pattern.


2. In most image sensors, the read-out pattern is pre-wired in silicon. It isn't like a memory chip where you read an arbitrary address. Rather, you set it into one of a few read-out modes, give a start trigger and then sequentially read-out all values coming out of a so-called channel (the K-7 sensor having 4 channels). Most image sensors deliver the values as analog voltages, some as digitized values (Sony Exmor).

Sure, as soon as sensors can be read-out like a memory chip (requiring 24-32 address pins and 12-16 pins per channel or 96 rather than 4 pins ...) then your idea (and many other) becomes feasible. But then there is reason #1.


Really, talking about the future, the most reasonable to do will be on-chip DACs (like Sony) and four times the number of channels per 2x2 Bayer cell so that in video mode, it can be binned into one digital 12:4:4 rgb channel to be read out. This is fast enough to read out 24fps video with 6fps cameras and would even allow 4k video on some future 43+ MP cameras. However, I haven't checked for power consumption of such a solution.

A simpler solution is Fujifilm's EXR binning on the sensor cells themselves. But it's only 2x binning. One would probably need 4x binning (e.g., 4x4 sensor cells into one pseudo 2x2 Bayer cell to be read out). This is possible with 39+ MP cameras.

On the other hand, high speed sensors like in the Casio Exilim achieve 6MPx60fps which would be 15MPx24fps or fast enough for a real-time read-out of all pixels. However, these modes are active for 1s or so and power consumption may be an issue. Nevertheless, the problem of sub-par video quality will soon be gone.

[RonHendriks1966]

K-7 Exposure Control in video with a fixed aperture:

• If it gets darker:
• first, K-7 increases exposure time to 1/30 s (at ISO 100)
• then, K-7 amplifies luminance up to ISO 3200
• then, the aperture reading blinks red
• If it gets brighter:
• first, K-7 dampens luminance down to ISO 100 (at 1/30s)
• then, K-7 decreases exposure down to 1/4000 s
• then, the aperture reading blinks red
• Additionally, the exposure can be locked (using the AE-L button) at any given EV value.

To my findings the shutterspeed is not going slower then 1/50 second.

A little more control on the issue would be nice.

I love filming with the K-7
This film was probably filmed at iso3200 and 1/50 second with the 55mm lens at f1.4 and external mic In black and White to avoid color-noise Spotmetering and AE-Lock

You Tube

You Tube

This film with the 21mm lens and lots of light from my studioset.

You Tube

You Tube

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Last edited by RonHendriks1966; 05-22-2010 at 02:03 PM.

[falconeye]

To my findings the shutterspeed is not going slower then 1/50 second.

This may well be the case. However, how did you measure it? AFAIK, a precise measurement is still due.

[RonHendriks1966]

This may well be the case. However, how did you measure it? AFAIK, a precise measurement is still due.

I compaired stills from the video with pictures made with the K-7 on 2 megapixel size. To my findings the iso3200 1/50 were the same.

[Class A]

This film was probably filmed at iso3200 and 1/50 second with the 55mm lens at f1.4 and external mic In black and White to avoid color-noise Spotmetering and AE-Lock

I felt I could see PF even in the B&W version.

More importantly, very good song and a very nice performance.

[SimonMW]

There are a lot of issues with the use of a DSLR for video. The issue of aliasing and moire is more down to lack of high pass filtering. The other problem is caused by the way that the separate RGB channels need to be derived. Effectively because of the single chip nature you're only getting about half the resolution you should be. That's why the Red One camera, although it has a 4k sensor, is only really a 2k camera. It can only reproduce 2k worth of actual resolution, even though the video file is 4k size.

This is why the new Arri Alexa is marketed as a 2k camera. They won't play the numbers game like Red, even though the Alexa has a 4k chip. It needs to derive the three separate RGB elements from that single chip, effectively halving the effective resolution.

The Canon 5D performs abysmally. On the tests that I have performed I have found that it only just squeezes past 600 TVL of resolution in both directions. Compare this to a Sony EX1 and EX3 which resolve 1000 TVL easily. What is puzzling is why this is the case because there are more than enough elements on the 5D chip to derive a full HD picture even with bayer separation.

The other trouble is that if you added a high pass filter to a DSLR permanently your stills photos would look soft. This is one reason that video and stills on the same camera can never really coexist properly.

With regard to the K7, Pentax really seriously need a firmware update that gives manual control to the shutter etc in video mode. Without that ability I will not touch that camera with a barge pole.