To ETTR or not to ETTR...?

Started 3 months ago | Discussions thread
knickerhawk Veteran Member • Posts: 6,262
Re: Have I got it right?
2

Barty L wrote:

timo wrote:

This thread seems to have got super-complicated. Have I misunderstood ETTR?

My understanding is that the further up the histogram you go (i.e. to the brighter end), the more useful data the file can contain, and that includes finer distinctions of tonal values.

Correct.

So for the purposes of taking the photo, you push the exposure up as far as you can SHORT OF blowing the highlights to the point where they are unrecoverable.

Avoid blowing highlights in areas where you want to retain detail. There is little or no interesting information in specular highlights or light point-sources, so you lose nothing by allowing them to blow.

The image will look overexposed at that point.

The image will appear 'over' exposed if the scene was low-key or made mostly of mid-tones, but might appear about right if the scene was very bright.

Then in post-processing, you bring the 'exposure', or 'brightness', or whatever you want to call it, back down to whatever reflects you visual intentions. That way you will get more subtle, more accurate, shadow tones. And better S/N ratio, provided you haven't had to adjust the ISO upwards, which would have defeated the purpose.

If, using the camera's metering system and with your EV dial set to 0, your shot is already just about triggering blinkies, you are already 'exposing to the right', and you don't have to adjust anything.

The camera might trigger blinkies on very bright parts of the scene, but those areas may not contain interesting information. If the brightest part of the scene in which you want to retain detail is not blinking, then you can profitably increase exposure until it is.

Remember that the blinkies are based on a JPEG (8-bit) representation of the scene. If you shoot RAW you have at least 12-bits to play with. A working rule-of-thumb is that highlights can be pushed +2.7 (on my E-M1 Mk1 anyway) stops above metered value and still retain detail. That might put you well into blinking territory, but highlights should still be fully recoverable.

Just to clarify for readers, that's assuming you're spot metering on the highlights you're referring to, which is not likely to be what you'd spot meter on when pursuing a non-ETTR, conventional metering strategy. As you note, it's important to test your own camera and raw conversion workflow to determine if the suggested exposure comp amount works well for you.

ETTR is most relevant in situations where there are no important extreme highlights, and you have a lot of shadow detail that you want to maintain.

ETTR is relevant in any and every situation where you feel the image could benefit from improved signal-to-noise ratios.

What have I missed?

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