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Old December 30th, 2007, 10:03 AM   #76
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Strange. Put the lens cap on. Put everything at 0db and flat color and post an uncompressed sample at 1/50sec.
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Old December 30th, 2007, 11:26 AM   #77
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Hello John,

1/50 sec shutter time, nearest neighbour debayer, gamma 1.8.

The first one is straight from QuickTime Player exported as png:
http://www.vosgames.nl/images/Mirage...tion-black.png

This one has been stretched with gimp:
http://www.vosgames.nl/images/Mirage..._processed.png
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Old December 30th, 2007, 11:45 AM   #78
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If you hadn't lowered the black levels a little bit (the right side a couple of codes above), it would have codes up to 16 with noise wtih a center around code 8. If this is 0db, that's a lot. It should be like that at about 9db of gain.
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Old December 30th, 2007, 12:14 PM   #79
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Hello John,

This is indeed with 0 db of gain (although how much that is reality I don't know). It is black compensated substracting some black lines from the whole image. So I didn't lower the black level.

left and right are of course from different halves of the sensor, with separate amplifiers and AD converter, so there is bound to be a slight difference between the two sides.

Although I would have expected there to be no more difference between left and right after subtracting the black lines, but there seem to be a slight slope vertically. This will probably be removed when I compensate for fixed pattern noise.

The fixed pattern noise is also contributing quite a bit to the noise you are seeing. In the end it will probably be very clean.

Cheers,
Take
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Old December 30th, 2007, 01:02 PM   #80
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The gain control for each tap is a true gain control. The only extra gain that could exist is for balancing the three colors. In some camera, the manufacturer provides up to 12db for this which covers most lighting situations. Your red and blue could already have a few dbs of gain from balance implementation. It is usually easy to tell in photoshop by switching between the channels. The noise difference should be obvious.

The Sony Z1 has noise with a center at around code 4. It doesn't change significantly with gain, so they obviously do extra processing. It's the ugly blocky type of course due to HDV.
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Old January 4th, 2008, 07:06 AM   #81
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Hello John,

You made me think again about my black level subtraction. As it is now, noise that is darker than black will be clamped to black. Also if parts of the sensor are darker than the black lines (non uniformity) they will also be clamped to black.

So I will be adding a constant offset to the sensor data, which will enable to me to represent a small range of negative values in 12 bits.

This should increase the quality of my per-pixel-non-linearity compensation algorithm.

Cheers,
Take
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Old January 4th, 2008, 08:57 AM   #82
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The noise is a little higher than it should be. Could it be an issue with your trigger? How do you power it?
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Old January 4th, 2008, 09:01 AM   #83
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Power and trigger is over firewire.
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Old January 4th, 2008, 09:30 AM   #84
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You mean it's a software trigger or a firewire trigger? Or firewire just for power? If you are just connecting a camera, perhaps the computer ports are not properly designed.
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Old January 4th, 2008, 09:42 AM   #85
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Hello John,

The trigger is based on the packet size you set and on how much data it wants to send. As the packets are put in the real-time stream on firewire, the trigger is basically the firewire clock. I will include a trigger based on SMPTE or word clock (simpler) at a later time.

I think the power/ground of the firewire connection is not clean. I've tried running the notebook from the internal battery, but there was no change, so the noise is picked up or caused by the notebook itself.

In any way, this is why I want to use fiber-firewire, and give the camera its own battery.
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Old January 4th, 2008, 10:26 AM   #86
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Depending on the camera and the interface, limiting free run with packet size is not dependable. You could do a long duration video to test. But this is not critical if you are just using a single camera and recording sync audio.
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Old January 4th, 2008, 10:36 AM   #87
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John,

It is even worse, with the packet size I can not even get it within 1% of 24 frame/sec. So I will have to make my own trigger.

Taking a word clock of 48000 and divide it by 2000 would be an easy route. Or maybe ask ambient to make a firmware change to output a frame trigger (it already does word clock, tri level sync and smpte) and it is battery powered.

In all probability I have to design some electronics, maybe based on a small microcontroller like the PIC, then I can add some buttons to the camera to change mode and shutter time. I also need a thermostat for the peltier element.

Cheers,
Take
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Old January 4th, 2008, 12:44 PM   #88
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1% is too much. What is the exact resolution and frame rate you want to get? 1920x800 24p 12bit?
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Old January 4th, 2008, 12:59 PM   #89
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John,

Yip, that is too much. But it will be no problem when I make an external trigger.

I am capturing 1920 x 940 x 12 bit @ 24 fps.
Then I do black levelling in software and crop the image to 1920 x 800 x 12 bit @ 24 fps.

The 12 bit is of course a sort-of-logarithmic conversion from the 14 bit A/D converter.

Cheers,
Take
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Old January 4th, 2008, 01:05 PM   #90
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That's very close to full frame. Nice:) You can actually get a very sharp 720p if you crop the scope sides to 16:9 and downscale.
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