ETTR – Expose to the Right
To improve signal to noise ratio (S/N), many professionals advocate ETTR (Expose to the right) when faced with low contrast scenes. The Luminous Landscape has two great articles by Michael Reichmann explaining this here and here. You might want to read them first before going on.
I decided to test this to see for myself if there was any value for my photography. Here’s the test scene:
- Canon 550D with a Nikon 50mm f/1.8 Manual lens at f/1.8. Shutter 1.5 seconds. ISO 400.
- Shot RAW, processed in DPP: Picture Style: Neutral. White Balance: Shade
Here’s the version exposed two stops higher, just below the clipping point for highlights:
This ETTR version was opened in DPP. The brightness (Exposure) was reduced by two stops. So it is matched to the ‘Basic’ version. No other changes where made. 16-bit TIFF files were exported and then crunched into 8-bit JPEGs at medium quality in PS for this test.
Here are the results at 200% Zoom:
It is obvious from the above exercise that there’s much less noise in the ETTR version. One must be careful about the following:
- It only works in RAW mode
- It’s only for low contrast scenes where ETTR is possible. One must be careful not to clip the highlights.
- In order to increase exposure, one must make a trade off in either Shutter speed, Aperture or ISO. Results will vary depending on the kind of work you do. You might realize the compromise you are making for better S/N is not worth the effort.
I urge you to read the articles in Luminous Landscape mentioned in the beginning of this post for a better understanding of this phenomena, and why DSLR sensors are not the same as film.