G1X Image Quality Comparison: FSAIQ vs Acuity for a range of compacts

Started Sep 25, 2012 | Discussions thread
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FauxMho Forum Member • Posts: 50
G1X Image Quality Comparison: FSAIQ vs Acuity for a range of compacts

Given the new cameras recently announced, plus the sometimes raucous discussion of the Canon Powershot G1X, I'd like to share with this community a figure I've maintained over the years comparing a range of compact digital cameras. Disclaimer: I am a rabid G1X owner and this is the analysis that convinced me to pre-order it soon after it was announced. For those who would like to cut to the chase, here is the figure:

This figure plots the FSAIQ (Full-Sensor Apparent Image Quality), as defined by RN Clark's excellent web site http://www.clarkvision.com/articles/digital.sensor.performance.summary/index.html#FSAIQ ) versus the acuity (in inverse arc-minutes - the human eye has a visual acuity of 1/arc-min). The FSAIQ takes into account the signal-to-noise ratio of the pixels and the resolution of the sensor limited by either pixel density or diffraction as appropriate. I do not account for aberrations in the lens, but for the sake of comparing cameras let's be consistent in ignoring aberrations for all cameras compared. I do use data on full-well capacities and noise from both Sensogen ( http://www.sensorgen.info ) and DXOMark. Acuity is obtained from the MTF50 resolution, again via the pixel density or diffraction limit as appropriate.

For comparison, the inset table and horizontal lines indicate the FSAIQ corresponding to Excellent Image Quality (40:1 signal-to-noise ratio) and Acceptable Image Quality (10:1 SNR) for a range of output displays. For those wanting to future-proof their work, I include 4K video and an as-yet imaginary 27-in iMac with Retina display.

Cameras included: I include most of the compact digital cameras I have owned and used (PowerShot A5, S30, S1IS, SD780, 300HS, G7, G9, G11, G12, and G1X), iPhone/iPad cameras, a number of hotly debated and new cameras (G15, SX40HS, S100, RX100), an EOS 7D with 17-85mm F4-5.6 zoom, and the long-term standard for compact high-IQ - the Pro1. For all cameras I've obtained the limited f-number versus focal length and used it to obtain the diffraction-limited Airy disk on the sensor. Each camera's curve (for those with a zoom) go from wide on the left to tele on the right, with loss of FSAIQ coming largely from the reduction in aperture with zoom.

Observations and Discussions:

0) Important note: all these numbers are for BASE ISO, so draw no conclusions from high-ISO performance here.

1) Note the clustering of cameras: the iPhone/iPad's with high 7-10 crop factors, ultra compacts like the SD780 and ELPH 300HS and the super-zoom SX40HS with 1/2.3" sensors, the 1/1.7" or 1/1.8" sensor cameras like the S and G series, the Pro1 and RX100 large sensor and/or fast lens 1/1.7" G15, and finally the G1X and 7D. With few exceptions, sensor size determines your IQ limits at a given Acuity/Resolution. Want to take excellent IQ photos? Get a large sensor.

2) The G1X is a pretty darn nice camera! For it's size and price, it has truly remarkable DSLR-class IQ. On the 112-mm 35mm equivalent tele end (right side of its curve), it has excellent print-quality IQ with high acuity that just out-resolves the 210-mm equivalent tele end of the G7/G9/G10. So no complaints of the 4x zoom on the G1X - it has the resolution to match or beat the long end of the G7,G9,G10,G11,G12,G15, and RX100.

3) On the subject of the RX100: while comparing it to the G1X is really apples and oranges from and IQ perspective, it really would seem to trounce the S100. Fast lens and large sensor gives the S100 a one-two knock out.

4) The Pro1 was REALLY ahead of its time, but the G15 really seems to match it well - except on the tele end where the Pro1 can muscle out the resolution. Differences in sensor technology and electronics may, though, give the G15 better performance relative to the Pro1 than these curves may suggest.

5) For all the talk of smartphones replacing cameras - yes and no. The ultra compacts are well matched by the iPhone 4S/5 camera, and given the rapid loss of IQ with zoom there is validity in statement that your smartphone can replace your camera. However, phone cameras have a long way to go to match the IQ and acuity of the 1/1.7", 1", and 1.5" sensors in these higher-performing compacts - and physics will keep it that way.

6) The SX40 has quite the following, but being a 1/2.3" sensor it really can't maintain IQ as it looses aperture on the tele end. I haven't worked the numbers for the SX50 - but its slower lens doesn't mode well in the IQ department. Fine daylight cameras, but I wouldn't travel with one as it's range of use will be sorely limited. The flat-aperture Panasonic (akin to the old S1IS) may be worth an analysis - if someone has the aperture vs zoom data please post.

7) I'm sure this figure won't go as far as the optimist in me would hope to settle some of the ongoing debates.

8) Errors and mistakes are all my own. Happy to fix 'em if you find 'em. First one: iPad3 is the same as "iPad Retina".

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