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Author Topic: Dynamic range of Leaf Valeo 22  (Read 3675 times)

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Dynamic range of Leaf Valeo 22
« on: September 09, 2003, 04:51:12 pm »

Well, there's what they claim and there's what it does. Two different things.

First of all there is a thoretical advantage to the Valeo 22 over the 10D because the MF back is a true 16 bit device while the 10D is a 12 bit device. This gives it a wider dynamic range.

Having said that, I now have tested two 16 bit MF backs, the Imacon 96 and the Valeo 22, and while both are 16 bit devices neither really show that much better a dynamic range than either my 1Ds or Kodak DCS Pro Back, both of whcih are 12 bit devices.

Michael
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Harrie Frericks

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Dynamic range of Leaf Valeo 22
« Reply #1 on: September 10, 2003, 01:48:16 pm »

Thank you Michael and BJL for your answers.

Michael, you've got me a little confused here. As far as I know dynamic range and bit depth are unrelated. For traditional film based photography dynamic range is the difference between DMax and DMin. For Digital Cameras it is, as BJL said, the difference between pure noise and maximum signal.

Bit depth only refers to the number of tones that are available between pure noise and maximum signal and is, basically, arbitrary.

Cheers,

Harrie
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victoraberdeen

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Dynamic range of Leaf Valeo 22
« Reply #2 on: September 12, 2003, 04:05:24 am »

This should be simple to understand, however the engineers are providing the data in electronic engineering numbers. I can cope with curves and fstops...

So Graph on page 9 seems to indicate that the read out frequency has a negative effect - maybe?

Dynamic range - 72db ??
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Harrie Frericks

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Dynamic range of Leaf Valeo 22
« Reply #3 on: September 09, 2003, 02:43:48 pm »

Michael,

Thank you for the review of the Leaf Valeo 22.

The Capture windows shows a dynamic range of -8 to +3 f-stops. Is this true? If so, why is it so much larger than my 10D? Is it because of the sensor, the firmware, the software?

Many thanks,

Harrie Frericks
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BJL

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Dynamic range of Leaf Valeo 22
« Reply #4 on: September 10, 2003, 09:50:23 am »

I do not know for the Leaf's DALSA (formerly Phillips) sensor, but it is probably not hugely different from the Kodak sensor which has a maximum dynamic range from pure noise to maximum signal of about 5000. That is very close to the noise level of rounding off to the nearest level in 12-bit linear A/D conversion (4096 levels), so going beyond 12 bits can achieve little, except for getting the numbers ready for standard 16-bit processing hardware.

The 10D almost surely has noticably less S/N ratio than these sensors (do not confuse noise levels in bright areas after in-camera processing with dynamic range!), so even with the same 12-bits in the A/D, noise will give lower dynamic range.

Just comparing bit counts in the A/D converters does not tell you much.  In brief, A/D converters seem often chosen to comfortably meet (i.e. exceed) the "luminance resolution" limits set by noise; why do otherwise if they are cheap enough? Sony plays the "superficially impressively big numbers" game by using 14 and even 16 bits A/D's in some digicams.
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BernardLanguillier

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Dynamic range of Leaf Valeo 22
« Reply #5 on: September 12, 2003, 03:18:42 am »

I believe that you are correct.

To put it another way, dynamic range is the lenght of the ladder, and bit depth is how many steps you have in it.

Best regards,
Bernard

BJL

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Dynamic range of Leaf Valeo 22
« Reply #6 on: September 12, 2003, 12:57:46 pm »

Quote
Dynamic range - 72db ??
This mystery number I can explain, having dug through the footnotes. It is simply "twenty times the log base ten of the ratio of the maximum electron count that a photosite can hold to the RMS variation in the electron count recorded by taking a photo in darkness"!  Quite transparent, I would think.

In more familiar photographic terms, you can divide this number by 6 to approximate the S/N ratio in "stops", or factors of two. So the maximum measurable signal level is twelve stops brighter than the noise.

Note that the noise measure is variation in signal, not average signal: the average value can be corrected for (like printing through film base plus fog level?); the variation is the visible "confetti" of noise.

Now, if you accept Kodak's suggestion that things need to be about ten to fourty times above noise to look good, which is roughly three to five stops, you get a usable subject brightness range of something like six to nine stops. Vague, but I do not think the theory justifies any more precise statement.
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