The Joy of Pixel Density

Started Jul 13, 2008 | Discussions thread
ejmartin Veteran Member • Posts: 6,274
Re: 400D Dynamic range not sensor limited

John Sheehy wrote:

ejmartin wrote:

John Sheehy wrote:

In the shot noise per unit of area, the
FZ50 pixels should outperform all DSLRs at all ISOs.

John, you've stated that your FZ50 performs better in terms of noise
for a given absolute exposure at ISO 100 pushed four stops than it
does at ISO 1600, which is the reverse of any other camera I know of.
It also flies in the face of the notion that the higher ISO
amplification tends to reduce noises when referred back to input
quantities like photoelectrons. I believe you called it a "Panasonic
engineering blooper". Could it be reflective of a problem with the
raw data being massaged by the camera at low ISO?

There are no signs of it; the sigma doubles with each 2x2 binning,
the noise is nice and sharp as you can see.

If so that would
seriously affect your conclusions; for instance, any sort of NR
performed before writing the raw data would throw off the inferred
sensor efficiency, by making it look more efficient than it is. As
it stands, this anomaly in ISO 100 vs 1600 is troublesome, because as
I said higher ISO amplification can only improve input-referred noise
performance.

The proof is in the pudding, though, and that is why I used a real
scene instead of a color checker - there is considerable detail 9 and
10 stops below saturation here; would that be possible with "massaged
noise"? When you look at an ISO 1600 Sony A700 image, the shadows
look all smoothed out. We have nothing like that here.

Oh, and BTW, the difference is not terribly large; massaging would
target a big difference, I would think.

Actually, it looks to my eye that in this comparison,

http://www.pbase.com/jps_photo/image/74342733

there is more and crisper detail in the ISO 1600 shot. And yet you say that ISO 100 has less noise (and indeed it looks that way). But it also looks a bit more smeared; could that be evidence of NR?

Is the gain (electrons/ADU) inferred from raw data proportional to ISO? That I think would be a quantitative test of whether there is some massaging going on in the raw.

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