How does ETTR work (Exposing To The Right)

Final Image
Editing the ETTR image has resulted in a full range of tones with rich colours and detailed shadows - and no blown highlights.

 

When your camera is pointed at a subject that is predominantly bright, the meter tends to under expose that subject. With experience, you will often adjust the camera exposure manually by over exposing a little. You can do this by opening up the lens aperture or slowing the shutter speed. Using exposure compensation is another method, but remember to set it back to zero when you have finished.

This is an exposure taken using the cameras meter reading or shooting in any of the auto exposure modes.

Standard TTL Exposure
The exposure given by the camera. Lots of brightness of tones has caused underexposure
You can see that all of the shadows are compressed and blocked out. That detail is gone, it cannot be recovered. Yet there has been very little information recorded on the right in the areas that can actually record much more digital image information.

Although the experienced photographer will make adjustments, there is a way to put the brightest point in the picture within 1% of blowing out, and therefore bringing in the rich shadow detail without muddiness and noise that would be more evident on the camera suggested exposure settings.

The sensors that modern cameras use are good enough to capture a very wide range of tones (its dynamic range or DR), so its easy to get an image where there are no blown highlights or loss of shadow detail. BUT, when you come to edit the image, trying to lift out any shadow detail from the bottom of the histogram just results in a noisy mess. Very little tonal information is recorded in the deep shadow areas, but much more information is available to the right of the histogram in the bright areas. So if we can accurately move our exposure right, just to the point of the highlights blowing, there will be much more detail in the shadow areas and a lot less noise.

 

The next image shows a correctly exposed file, the highlights are at the far right and the shadows are recording much more information as they have been towards the centre of the histogram. Yes it does look overexposed, but it is in fact a file with the best possible amount of image data to edit.

Exposing to the right (ETTR)

 
 

 

So how was this achieved?

I have calibrated my Sekonic L-758D light meter with the characteristics of the dynamic range of the sensor in my camera. I took a spot reading from the brightest part of the subject. Now of course the meter then placed that brightest point to the mid tone (18%) grey,
which would result in an underexposed image. As I have calibrated the meter to my camera, I know that I can shift that highlight reading 3.4 stops, which puts the highlights at the clipping point and allows the shadows to more right as well. The image looks overexposed, and as shown in the image on the right, the highlight warning preview on the back of the camera was blinking away!

Illustration of highlight warning on camera LCD
Illustration of highlight warning on camera LCD

The image preview is actually a jpeg representation of the raw image file recorded. If you are shooting with RAW files, and expose so that the image on the back of the camera is not displaying highlight alerts, then you are throwing away at least 1.5 stops of information that could be used. moving the shadows 1.5 stops right on the histogram can result in almost 4 times more data to be recorded. Even an excess of one bright colour can have the preview highlight alert going mad, even though it will not be over exposed.

If I had used my hand held meter to take and incident light reading, it would have improved the camera suggested exposure, as it would measure the light intensity falling onto the subject, not that being reflected back. It is therefore not fooled by a very dark or light subject.

Here is an edit of the over exposed looking image shown above.

Final Image
Editing the ETTR image has resulted in a full range of tones with rich colours and detailed shadows - and no blown highlights.

The file was so easy to edit, no pulling and pushing of highlights or shadows. rich colours and plenty of detail.

So next time you are out and about, have a go at manually exposing to the right, don't believe your histogram, and enjoy the revelation of RAW files with more detail that you ever though possible.

Graham Taylor

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One thought on “How does ETTR work (Exposing To The Right)

  1. Thank you for sharing your info. I truly appreciate your
    efforts and I will be waiting for your next write ups thanks once again.

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