Re: [OM] TOP - DxO Gives OM-D High Marks

Subject: Re: [OM] TOP - DxO Gives OM-D High Marks
From: Ken Norton <ken@xxxxxxxxxxx>
Date: Mon, 1 Oct 2012 16:32:19 -0500
> Don't mention it. If I didn't look daft, I'd be invisible.

Then I suppose that we must have looked like the daft twins photographing
in the rain.

The premise of my statement surrounds the nature of the digitizing process.
No two types of sensors see light and color in exactly the same way. During
the analog-to-digital process, there are offset gains applied to the sensel
measurements to correct for this. The offset gains, are essentially done in
the same manner as applying gain for higher ISO settings, but are applied
to the individual color banks. This is done prior to the creation of the
raw file as it is applied at the sensor level or in the chip used for the
actual A-D conversion.

This is a vital step because you want to have the color normalization
characteristics applied during the digitization process (or even before)
because once the raw file is created, the brightness levels and gamma
characteristics are baked in. The typical A-D converter in our cameras is
usually around 12 to 14-bits. If the image data wasn't normalized prior to
the digitization, you could end up with many of those bits effectively
thrown out the window and unusable.

For illustration sake, let's say that Panasonic and Sony both developed a
16MP sensor for the OM-D. (not far fetched, I'm sure. hehehe). What is the
likelihood that both sensors had exactly the same sensitivity and linear
response? Considering that the color filters themselves vary a bit and the
pixel fill-factor is different, the chances that both are exactly the same
are nil. Just for argument sake, let's make an assumption that the
Panasonic sensor is 10% more sensitive to greens than the Sony sensor. To
maintain same WB, we would have to dial in an adjustment on 100% of the
images. What the manufacturers do instead is apply an amplification offset
(gain adjustment) to the chip to give the sensor a standardized
white-balanced so no further correction has to be done. Without this
amplification offset, once the digital conversion happens, in order to
maintain white-balance, you will lose up to 10% of the dynamic range.


Ken Norton
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