Re: Panasonic LX-3 Review
Posted: Fri Oct 24, 2008 8:59 am
OK, I have had a chance to analyze some of the data from Canon G10 files that Bill Lockhart was kind enough to provide...
G10 @ ISO 80 (green channel, probably the same for R,B as well):
Black RAW level: 128
Saturation RAW level: 4095
photosite efficiency: 1.28 e-/raw level
Full well capacity (e- at raw saturation): 5080 e-
Read noise: 6.5 raw levels = 8.3 e-
Photosite dynamic range: 9.26 stops
Here is a sample crop from a black frame RAW; the range of levels 100-150 spans 0-255 on your monitor:
Banding is pretty reasonably controlled; what there is has a kind of funky pattern in its spatial frequency content (if you're interested in the unnormalized Fourier spectrum, it's here).
The photosite efficiency is excellent. I have compiled 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 G10 photosite efficiency to ISO 400 by dividing by 5=400/80, and dividing also by the pixel area (1.72µ)^2, gives an efficiency figure of merit of .087 electrons per raw level per square micron. Naively this is about the same as the Nikon D300, however it should be kept in mind that DSLR's meter middle grey at about 3.5 stops down from raw saturation, while the G10 meters middle grey at about 2.5 stops down from raw saturation. What this means is that the G10's stated ISO is about 2/3-1 stop lower than a DSLR's stated ISO (this is rather standard for digicams that their native sensor ISO is differently normalized); this would raise the figure of merit by a factor of 1.5-2, and therefore, square micron for square micron, the G10 sensor is about the best in the business. Its problem of course is that it doesn't have enough of those square microns -- sensor dimensions 7.6mm x 5.7mm, instead of FF 36x24, 20 times smaller in area.
Here is the photosite S/N ratio (vertical axis, in stops) as a function of raw level (horizontal axis, in stops):
While I haven't tested higher ISO's, it is pretty typical on CCD digicams that the only effect of higher ISO on the raw data is to remove a stop of highlight DR for each stop increase in ISO. If you want to compare to what a DSLR can do, see
http://theory.uchicago.edu/~ejm/pix/20d ... tml#SNR-DR
Finally, it is good to remember that noise is scale dependent. To compare with other cameras, pixel level noise should be divided by the square root of the MP count (14.6MP; sqrt[14.6] is about 3.8 ) to get a noise figure of merit at roughly comparable spatial scales (rather than at the pixel level, whose spatial scale varies with the MP count). The G10 at ISO 80 seems to have roughly the same S/N as the 1D3 at ISO 1600 (a little better in highlights, a little worse in shadows).
Next up, the LX3, as soon as I get the needed RAW files.
G10 @ ISO 80 (green channel, probably the same for R,B as well):
Black RAW level: 128
Saturation RAW level: 4095
photosite efficiency: 1.28 e-/raw level
Full well capacity (e- at raw saturation): 5080 e-
Read noise: 6.5 raw levels = 8.3 e-
Photosite dynamic range: 9.26 stops
Here is a sample crop from a black frame RAW; the range of levels 100-150 spans 0-255 on your monitor:
Banding is pretty reasonably controlled; what there is has a kind of funky pattern in its spatial frequency content (if you're interested in the unnormalized Fourier spectrum, it's here).
The photosite efficiency is excellent. I have compiled 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 G10 photosite efficiency to ISO 400 by dividing by 5=400/80, and dividing also by the pixel area (1.72µ)^2, gives an efficiency figure of merit of .087 electrons per raw level per square micron. Naively this is about the same as the Nikon D300, however it should be kept in mind that DSLR's meter middle grey at about 3.5 stops down from raw saturation, while the G10 meters middle grey at about 2.5 stops down from raw saturation. What this means is that the G10's stated ISO is about 2/3-1 stop lower than a DSLR's stated ISO (this is rather standard for digicams that their native sensor ISO is differently normalized); this would raise the figure of merit by a factor of 1.5-2, and therefore, square micron for square micron, the G10 sensor is about the best in the business. Its problem of course is that it doesn't have enough of those square microns -- sensor dimensions 7.6mm x 5.7mm, instead of FF 36x24, 20 times smaller in area.
Here is the photosite S/N ratio (vertical axis, in stops) as a function of raw level (horizontal axis, in stops):
While I haven't tested higher ISO's, it is pretty typical on CCD digicams that the only effect of higher ISO on the raw data is to remove a stop of highlight DR for each stop increase in ISO. If you want to compare to what a DSLR can do, see
http://theory.uchicago.edu/~ejm/pix/20d ... tml#SNR-DR
Finally, it is good to remember that noise is scale dependent. To compare with other cameras, pixel level noise should be divided by the square root of the MP count (14.6MP; sqrt[14.6] is about 3.8 ) to get a noise figure of merit at roughly comparable spatial scales (rather than at the pixel level, whose spatial scale varies with the MP count). The G10 at ISO 80 seems to have roughly the same S/N as the 1D3 at ISO 1600 (a little better in highlights, a little worse in shadows).
Next up, the LX3, as soon as I get the needed RAW files.