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Author Topic: Camera's histogram reliable to the RAW data  (Read 254656 times)
John Sheehy
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« Reply #100 on: January 17, 2008, 06:42:39 PM »
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That 1000 levels are lost to read noise.
The chart clearly shows the relative contributions of read and shot noise for the exposure zones, and shot noise predominates in the green area of the chart, which comprises 4080 levels, whereas read noise dominates only in the very deep shadows, comprising 15 levels at most. How can you lose 1000 levels to read noise, when it predominates in only 15?
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OK, now your objection is clearer.

First of all, the issue I addressed has nothing to do with how much of the recorded range has more read noise than shot noise (and read noise is significant far above this range, especially if there is 1-dimensional or "banding" noise, which is much more visually potent than 2-D noise).  The issue is *what* the level of read noise is in ADUs, as this will be the minimum noise found anywhere in the image, in a linear sense, relative to the steps of the digitized levels.  If quantization doesn't happen where there is only read noise, it shouldn't happen at any other range, where shot noise increases the absolute noise level.

The premise is that with a read noise of 2.0 ADU at ISO 100 in the 5D (not the same as the 1Dmk2), the number of levels used can be divided by 2.0/1.4, or 1.43, without incurring any practical quantization in the RAW data.  The other way to look at it is that the steps can become 1.43x their current size.  In this case, that would mean that the number of levels between black and RAW saturation in the 5D at ISO 100 could just as well have been recorded with about 1000 less levels (about 2500 instead of about 3500).  It is not about clipping levels away from the shadows (or highlights, or anywhere).
« Last Edit: January 17, 2008, 06:43:46 PM by John Sheehy » Logged
Guillermo Luijk
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« Reply #101 on: January 20, 2008, 08:37:07 AM »
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Just curious: http://blog.lexa.ru/2008/01/16/balans_belo...inim_gisto.html

This guy performs the Hue/Sat analyse with PS. Russian document.
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Guillermo Luijk
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« Reply #102 on: April 12, 2008, 02:38:16 PM »
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Sorry to recall this post, but a forum member of POTN forum has depicted (http://photography-on-the.net/forum/showthread.php?t=485349) a much easier way to obtain a UniWB on any camera than my whole procedure: the point is that what we are seeking for is an image which is already balanced (R=G=B ), so that when the camera tries to calculate the WB multipliers over it, they will be the closes possible to 1.0 1.0 1.0.

And which is the easiest to produce already balanced image? any shot where all three channels are saturated on every pixel, i.e. pure white, and that's as simple as shooting your camera to the sky or any bright area with the lens wide open for some seconds. Once we use the resulting image for in-camera WB calculation, the multipliers will be the closest to UniWB.

I have done this in my camera and achieved multipliers:

multipliers 1.006856 1.000000 1.005877 1.000000

I cannont improve that, surely because some hot pixel or whatever. A a max error of 0.69% for the R channel is simply outstanding.

Regards.
« Last Edit: April 12, 2008, 02:39:48 PM by GLuijk » Logged

ride5000
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« Reply #103 on: February 20, 2009, 03:18:27 PM »
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Quote from: GLuijk
Sorry to recall this post, but a forum member of POTN forum has depicted (http://photography-on-the.net/forum/showthread.php?t=485349) a much easier way to obtain a UniWB on any camera than my whole procedure: the point is that what we are seeking for is an image which is already balanced (R=G=B ), so that when the camera tries to calculate the WB multipliers over it, they will be the closes possible to 1.0 1.0 1.0.

And which is the easiest to produce already balanced image? any shot where all three channels are saturated on every pixel, i.e. pure white, and that's as simple as shooting your camera to the sky or any bright area with the lens wide open for some seconds. Once we use the resulting image for in-camera WB calculation, the multipliers will be the closest to UniWB.

I have done this in my camera and achieved multipliers:

multipliers 1.006856 1.000000 1.005877 1.000000

I cannont improve that, surely because some hot pixel or whatever. A a max error of 0.69% for the R channel is simply outstanding.

Regards.

thanks for the update Guillermo!

-ken
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erick.boileau
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« Reply #104 on: December 19, 2009, 01:29:53 AM »
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I am having a 5D Mark II (and a MAC)   what can I use instead of DCRAW ?
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Guillermo Luijk
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« Reply #105 on: December 19, 2009, 08:11:39 AM »
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Quote from: erick.boileau
I am having a 5D Mark II (and a MAC)   what can I use instead of DCRAW ?
DCRAW works for Mac and the 5D2. There is a download link here.
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erick.boileau
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« Reply #106 on: December 19, 2009, 08:22:52 AM »
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thank you
« Last Edit: December 19, 2009, 08:26:38 AM by erick.boileau » Logged
erick.boileau
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« Reply #107 on: December 19, 2009, 09:37:35 AM »
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it is what you get directly with a Digital Back PhaseOne P45

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