Contrary to conventional wisdom, higher resolution actually compensates for noise

Sunday November 16 2008

Camera Article
Introduction | Modeling small pixels | Comparing the SNR of cameras with different resolutions | Real-life comparisons | Conclusion

Consider the data on 5 full-frame DLSRs shown in the table below. They all have different resolutions. Note that the result for the Nikon D3 puts it far ahead of the other models in terms of RAW noise, followed by the Canon EOS 5D.

The normalized SNR for an equivalent resolution 8Mpix shows the Nikon D3 keeping an easy lead, but the difference between the EOS 1Ds Mark III is no longer huge. Further, the relatively low resolution of the EOS 5D lowers its performance compared to the higher-resolution sensors by the same manufacturer, making the comparison with a normalized resolution more relevant. Indeed, the images are not meant to be visualized at 100% zoom on a regular screen, since only a small part of the image is visible. On the other hand, the images can be printed using different and possibly large formats.

 

Model

Release date

Pixel pitch (µm)

Resolution (Mpix)

SNR 18% (effective ISO 200)

Normalized SNR 18% (effective ISO 200)

Nikon D3

8/23/2007

8.5

12.2

38.99

40.82

Canon EOS 1Ds Mark III

8/20/2007

6.4

21.5

35.05

39.35

Canon EOS 1Ds Mark II

9/21/2004

7.2

17.1

35.12

38.42

Canon 1Ds*

9/4/2002

8.8

11.1

34.72

36.14

Canon EOS 5D

8/22/2005

8.2

13.2

35.99

38.17

*While the Canon 1Ds is far behind, note that it was the very first full-frame DSLR.

 

Normally, the user cannot access the effective or “real” ISO through the camera settings, but must rely on the ISO announced by the manufacturer, which is usually different. However, DxO Labs has carefully tested the above cameras to compare absolute ISO values with the ISO values announced by the manufacturers (see the results).

Effective ISO values provide the most relevant comparisons: images are shot with the same sensitivity—that is, shadows and highlights are preserved or lost in the same way, thus preserving the ranking when converting the RAW images using the same RAW converter. If we look at the minimal ISO setting (thus the maximal SNR), we see that the lowest ISO setting for Nikon D3 is ISO 200, whereas it is 100 for the Canon DSLRs. The noise measurements at minimal sensitivity are shown below.

 

Model

Manufacturer min ISO

Effective min ISO

SNR 18% Max

Normalized SNR 18% Max

Nikon D3

200

131

41.03

42.86

Canon EOS 1Ds Mark III

100

70

38.58

42.89

Canon EOS 1Ds Mark II

100

79

38.19

41.49

Canon 1Ds

100

93

37.92

39.34

Canon EOS 5D

100

88

38.75

40.93

 

 

In this case, the EOS 1Ds Mark III and D3 are tied. However, the 1Ds Mark III image will be underexposed compared to the D3 (about 1Ev in manual mode), or the exposure time will be twice as large (assuming that auto-exposure strategies are the same).