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The new "advanced compact" category that adds DSLR features (such as RAW output, manual operation, and interchangeable lenses) to classy, compact-style cameras, continues to be populated with new models—e.g., Canon Powershot G11 and S90, Olympus EP1 and EP2, Panasonic GF1, Leica X1, etc.

In this review we focus on the evolution of sensor characteristics and performance within this category, considering the Canon Powershot G11 and S90 and the Olympus E-P1 models in particular, and show how top models are catching up with entry-level DSLRs in terms of RAW image quality.

Fewer pixels for the new G11 and S90 models from Canon

If we look at the G models from G9 to G11, we see that Canon kept the sensor size constant while first increasing the resolution, going from 12Mpix for the G9 to 15 Mpix for the G10. Then with the G11 and the latest Powershot S90, Canon decreased the pixel count to only 10Mpix. We can see the impact of such changes on RAW image quality by analyzing these models’ DxOMark data and scores.

Looking at the table below, again considering that the actual sensor surface is the same for all three models, the added pixels from G9 to G10 increase the Sensor Overall Score from about 35 to 38 (5 points correspond to 1/3 of a stop). That's a small increase, below the 5-point “significant” threshold, and confirms that increasing resolution results in additional information that evenly balances the added noise due to smaller pixel size (as outlined in our previous Insight, "More pixels offset noise").

Both the G9 and G10 exhibit fairly high noise levels in low light—and Canon had to do something about it. With the G11 and the S90 (both featuring the same sensor), Canon chose to stick with the same sensor size, but significantly decreased the pixel count. As sensor size did not change, all other factors being equal, Sensor Overall Scores should have stayed about the same. The 8-point Sensor Overall Score difference between the G11/S90 and G10 shows that Canon definitely made some improvements to pixel and/or processing technologies to achieve this image quality improvement. If we consider the details of the Sensor metrics, in particular the +1EV gain (Max DR=11.1EV) versus the G10 (DR = 10EV) for Dynamic Range, one possible explanation for the 8-point gain is that Canon improved the pixel signal read-out electronics and/or the A/D converter.

Larger sensor area with Olympus EP1 and EP2 advanced compacts

Olympus has taken a different approach with its EP1 and EP2 advanced compact models. As the designer of the smallest DSLR (the E-x 4/3 format series), Olympus has integrated its 4/3 sensor (featured in the E-620 or E-600 models, for instance), which has performed quite well.

DxOMark data clearly backs up the image quality performance for that category, as shown in the table below. The EP1 scores 55 on the Sensor Overall Score—almost 10 points (2/3 of a stop) higher than the G11. With the larger sensor size, pixel size is twice as large for the Olympus than for the G11 (meaning that the Olympus receives 4 times more light per pixel). The larger pixel size means much less noise, especially at low light levels, as the Low-Light ISO metric clearly shows: 536 for the EP1 versus 165 for the G11.

From a sensor performance perspective, then, Olympus, with its 4/3 sensor, leads the race within this new category. However, even with their large sensor format, Olympus models still do not reach the quality of the latest entry-level DSLRs, such as the Canon 1000D (Sensor Overall Score = 61.6), Nikon D3000 (62.4) , and Sony A230 (63.4).

Now let’s consider the image quality performance of the G11, S90 and EP1 with respect to their sensor size, taking the full-frame Nikon D3x as the reference (Sensor Overall Score = 88) and computing the performance of the three advanced compacts when normalized against their respective surface areas.

On the following table we show the surface ratio of each model versus the full-frame Nikon D3x and report the Sensor Overall Score for each as if it were dependent only on size (i.e., assuming that they all have the same pixel and read-out technologies):

(Note: +15 points on Sensor Overall Score shows a 1-stop increase for performance, and similarly, 2X for the surface sensor also adds 1 stop to the image quality performance. Read more on Sensor Overall Score definition)

Looking at these numbers, the Olympus EP1 should have lost 28 points, but it actually loses 33 points (88 – 33 = 55), whereas the Canon S90 and G11 lose only about 42 points (88 – 42 = 46), when it should have lost 65 if all other factors except surface were equal.

One can conclude from this analysis that the Canon G11 and S90 sensor has a much higher performance per unit of surface than the Olympus EP1 or the Nikon D3x sensors.

Conclusion

Overall, manufacturers for this category are making every effort to increase imaging performance, and while they are not all taking the same path, they have been quite successful in developing compact cameras that are only 1 to 2 stops away from entry-level DSLRs. This has been possible thanks to a lot of innovation in designing very efficient small-pixel technologies. Taking into account the particularly impressive performance of the Canon S90 and G11’s sensor per unit of surface, we can expect even more progress in the future.

Finally, we want to underscore one other innovative feature that helps to further boost image quality: the RAW shooting capability offered with the advanced compact models. As is well known, photographers can capture the highest dynamic from the scene by shooting in RAW, and then by using the most advanced PC or MAC RAW conversion software solutions, they can recover 1 to 2 stops, thereby pushing the image quality performance of these cameras very close to that for DSLRs.

Disclaimer: This DxOMark review evaluates only the selected camera’s RAW sensor performance metrics (i.e., Color Depth, Dynamic Range, and Low-Light ISO), and should not be construed as a review of the camera’s overall performance, as it does not address such other important criteria as image signal processing, mechanical robustness, ease of use, flexibility, optics, value for money, etc. While RAW sensor performance is critically important, it is not the only factor that should be taken into consideration when choosing a digital camera.