Anyone with some 8bit DSP insights? - Page 2 at DVinfo.net

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Canon XL and GL Series DV Camcorders
Canon XL2 / XL1S / XL1 and GL2 / XM2 / GL1 / XM1.


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Old July 14th, 2004, 06:42 PM   #16
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Wow. Thanks Don. I simply asked the USA product manager. But then again, he didn't build the thing. Let me bring this up with him. Appreciate the info!
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Old July 15th, 2004, 09:03 PM   #17
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Be interestig to hear what he has to say.
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Old July 16th, 2004, 07:04 AM   #18
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He says that he does not have that information, which can mean only that I must have been hallucinating earlier. So my chart is now changed to reflect that it is unknown, or at least not known to be factual. I'm told that when an answer comes back from Japan as to what the bit depth really is, then "they'll let me know." That's the official word. I have asked once and I will not ask again.
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Old July 17th, 2004, 11:04 AM   #19
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Very interested in seeing the real world tests of the 12 bit vs. the 8 bit.

Cinamtography.com's forums have some pretty negative statements about the camera, especially dealing with this issue;
http://www.cinematography.com/forum2004/index.php?showtopic=1611&st=30 Check out Mitch Gross's post.

It also makes me wonder why people want HDV so badly, considering that is a 4 bit color space. And with side by side comparisons that I have shot with a PD170 and anamorphic adapter next to the JVC HDV camera, and with the DV being blown up to HD and with zero color correction, the PD170 blew away the JVC in color fidelity. The skies actually looked kind of pink with the JVC.
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Old July 17th, 2004, 11:40 AM   #20
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Color can be corrected. Resolution cannot.

Canon I'm sure does not want to play up the fact that they are not using 12bit as on other professional cams.
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Old July 17th, 2004, 07:43 PM   #21
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Let me see if I can help.

The analog CCD sends a signal as a voltage level to an analog to digital converter. It actually passes through some filters first, however that is not relevant here.

If it is converted to an 8-bit value their are 256 different levels for the signal. 10-bits provides 1024 levels. 12-bit provides 4096 levels. And the 14-bit value in some Sony camera's provides 16384 levels.

Now lets say you do a black stretch. and in that stretch the values from 0-20 IRE are stretched to 0-40 IRE (ok, that is too big, but the math is easy). Now in the final 8-bit value that range (0-40) is 100 of the 256 values.

With 8-bits you start with 50 possible values, expand to 1000 and interpolate the others (information is made up). With 10-bits you have 200 possible levels and interpet them to 100 levels (information is lost, however the resulting information is a result of more knowledge than you need). With 12-bits there where initially 800 levels; with 14-bit there were initially 3200 levels.

If black stretch were the only adjustment, then 10-bits would be all you need. However each of those adjustments cascade the the size of the area that needs to be enlarged. Change detail, shift color, everything requires taking a smaller area and making it cover a larger area. As does white balance and of course gain.

The more bits of information you have, the less likely you are making up information. The smaller differences you have to work with.

So, 8-bit, 10-bits, 12-bits, it means a lot. A better question: How important is the difference between 12- and 14- bits? Does Sony have an advantage?
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Old July 17th, 2004, 08:11 PM   #22
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In a scene with a dynamic range of 5 stops (256 levels, typical for DV) the first stop (highlights) uses 128 levels. The second stop uses 64 levels, the third 32 levels, the fourth 16 levels, and the last 8 levels. Can you try your explanation again?
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Old July 17th, 2004, 08:59 PM   #23
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I made the example linear because: it is simplier, I don't have the algorithms used for compression (crushed blacks is not an algorithm), and the example serves its purpose regardless of complexity.

What the extra data does is provide a way to peform the various transformations (I didn't list gamma, knee, and others) and still have good data. And all of the computation in the world can't recreate data that isn't there, it can only estimate what it may have been.

Canon did what it did because of time and financial contraints. I heard a rumor (I can't reveal the source) that Canon may add Matshuisha electronics (JVC and Panasonic) in the future.

XL2S?

Also heard a rumor that the DVX100B may finally have the 16x9 CCD in 2005. And my wife was sure we were going to win that last big lottery.
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Old July 17th, 2004, 09:17 PM   #24
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My example is linear also. When you close you lens one stop you have reduced the light striking your CCD by 50%. If you have 256 levels, then 128 levels are required to represent the first 50% of the light reaching the CCD. In 10 bit you would have 1024 levels and a one stop reduction in light would use the first 512 levels.

There is no arguing that more data will yield a better image. However, is the chip capturing 8 bit data and it's being up-sampled to 10 bit or 12 bit, processing applied and then down-sampled to 8 bit for recording to tape? Or do they actually capture 10 bit or 12 bit data, process it and down-sample to 8 bit for recording?
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Old July 17th, 2004, 09:39 PM   #25
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The CCD doesn't capture bits. It captures analog voltage. The A/D converter turns that into bits.

If you have $2,529.65 cents in your pocket and I let use store two digits of data, you have $2,500. If I give you three you have $2530. If you have 4 then still $2530, however the last digit is significant. 6-digits gives you the full value.

If the range of the conversion was $0-100,000, then two digits only would give you $3k. That is the information lost.

The unless you modifed the signal when it was still analog, all of the allocation is done digitally. I don't know the specifics of the implementation in camcorders.

Saying it is a 12-bit DSP may be misleading. For our purposes it is probably more accurate to say their is a 12-bit A/D conversion. Or an 8-bit A/D conversion.

You could process 12-bits in a 4-bit DSP or a 24-bit DSP. That is a matter of speed. Remember 8-bit and 16-bit computers. They could still process 32-bit numbers, just not in one step.
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Old July 17th, 2004, 09:51 PM   #26
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I'm aware that CCD's are analog , not digital, but you are correct and I should be more accurate in my descriptions. I think you're making assumptions regarding signal processing. You think the reference to 10 bit DSP is the data processing and not the bit depth? What is the source of this information and who is the manufacture of these chips?
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Old July 17th, 2004, 10:06 PM   #27
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The Canon uses an 8-bit A/D converter. The Panasonic a 12-bit. I'm not confusing it. I trying clarify it.

The reference to the DSP is always processing. JVC (which uses a 12-bit signal) advertises a 24-bit DSP. Still a 12-bit signal.

This is how Panasonic describes it (on the first text page of their brochure):

"High Image Quality with 12-Bit A/D Conversion

"The AG-DVX100A features an A/D converter that uses the same 12-bit processing as broadcast camera-recorders. Precisely digitizing the gradation and colors captured by the progressive CCD, this A/D converter supports gamma switching and other fine downstream image adjustments — one of the keys to achieving rich image expression."

DSP is never mentioned in their brochure.

JVC said about there DV5000:

"the GY-DV5000 is a highperformance 1/2" 3-CCD Professional DV camcorder which includes advanced features such as a 12-bit ADC (used only in broadcast cameras), a 12-bit camera digital signal processor for superior, high-resolution images, ...".

And about the DV300:

"Newly-developed 12-bit ADC* and 24-bit DSP** The 12-bit ADC allows direct digital input to the DSP without passing through analog pre-gain and pre-knee circuits, eliminating signal degradation. In addition, JVC's new DSP with advanced 24-bit video processing brings out natural details, eliminates spot noise, and accurately reproduces dark areas.
* ADC: Analog Digital Converter ** DSP: Digital Signal Processor"

Sony says about the PDX-10:

"14-bit DXP (Digital Extended Processor)

"The use of 14-bit A/D conversion combined with 14-bit digital processing drastically reduces the noise commonly seen across dark areas of a picture. This precision of digital processing also contributes to expanding the dynamic range of the camera so that both dark and light areas of a picture are reproduced with more contrast, thus reducing the wash-out effect."

And about the DSR570 and DSR370:

"10-bit A/D DSP (Digital Signal Processing) LSI

"The advanced Sony 10-bit DSP technology used in these camcorders delivers one of the best picture performances in the industry. Optimized digital-signal processing ensures excellent picture sharpness. And innovative camera features such as TruEye™ and DynaLatitude™are also incorporated."
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Old July 17th, 2004, 10:25 PM   #28
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thanks for taking the time to quote the manufactures brochures. David, we're misunderstanding each other. You and I are basically saying the same thing.
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Old July 26th, 2004, 05:27 AM   #29
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Where does it say the Canon uses 8-bit DSP or A/D conversion? (It is not a quote from any Canon literature that I've seen.)

The original XL1 service manual and schematic show 10-bit A/D conversion with the LSB discarded as it is passed to 9-bit DSP. Gain, white balance, and pedestal adjustments are in the analog section before the A/D conversion. It becomes 8-bit after DSP as an encoded DV signal for recording on tape.
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Old July 26th, 2004, 07:57 AM   #30
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That came from a Canon marketing manager who went to research it and came back.

What you said is interesting. The XL1 had a 10-bit A/D with 9-bits used for processing? I would have assumed that the XL2 would have had at least the equivalent.

And, it is not in any of the literature. Its absence is what made the question necessary.
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