LX3 sensor analysis

Started Oct 31, 2008 | Discussions thread
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ejmartin Veteran Member • Posts: 6,274
LX3 sensor analysis

Some people have expressed an interest in the capability of the LX3 sensor, and thanks to a few people willing to take a series of RAW images to my specifications, I was able to infer some of its properties. If you have no interest in this sort of thing, please move quietly on to another thread.

I have to say, I am quite impressed with the LX3's sensor; I couldn't believe the efficiency number when I first got it. Here are the sensor properties at base ISO, ISO 80:

Black RAW level: 16 (but blacks are clipped)
Saturation RAW level: 4095
photosite efficiency: 2.20 e- raw level
Full well capacity (e- at raw saturation): 9000 e-
Read noise: 2.55 raw levels = 5.6 e-
Photosite dynamic range: 10.6 stops

The photosite efficiency is superior; my LX1 only gets about half that (the read noise is also substantially better than the LX1). I have compiled photosite efficiency results for a number of DSLR's at
http://theory.uchicago.edu/~ejm/pix/20d ... #pixelsize

see Table 1 a bit further down the page. Translating the LX3 photosite efficiency to ISO 400 by dividing by 5=400/80, and dividing also by the pixel area (2µ)^2, gives an efficiency figure of merit of .106 electrons per raw level per square micron. Naively this is better than the 1D3/1Ds3, and just a bit short of the D3, on a per area basis. However, the relative normalization of the ISO needs to be measured to correctly compare.

Here is the photosite S/N ratio (vertical axis, in stops) as a function of raw level (horizontal axis, in stops):

The LX3 is the blue curve, the G10 the red curve. The LX3 plot is not far from the 1D3 at ISO 800 (!); see
http://theory.uchicago.edu/~ejm/pix/20d/tests/noise/noise-p2.html#SNR-DR

Please note also that these are pixel S/N ratios; image S/N involves the S/N at a fixed spatial scale relative to frame height, which involves scaling the pixel S/N ratio by the square root of the MP count. Translated into stops, the G10 curve should be raised by about .25, bringing it closer (but still short of) the LX3 curve.
--
emil
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http://theory.uchicago.edu/~ejm/pix/20d/

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