To ETTR or not to ETTR...?

Started 3 months ago | Discussions thread
Xasan Contributing Member • Posts: 828
Re: To ETTR or not to ETTR...?

tomhongkong wrote:

Some facts

Most people use an average auto exposure setting which is based on averaging the light measured and having an 18% greyscale exposure correct.

You are missing at least one important fact, AE determines what it is in the scene to be assigned 18% to, and in certain modes it doesn't bother to do even this. 18% greyscale exposure of what is going to be correct? Of an 18% card filling the frame? How useful is that IRL?

Before you go into explanations you need to have a clear idea what is AE and how it works, and what you know about the multitude of AE algorithms in use.

That means that bright portion of a bright image is going to be underexposed (of course if you are using spot or centre weighted exposure that may not apply). A predominately dark image might similarly be underexposed

With most digital sensors there is around one stop of 'headroom' for highlights, when the auto exposure is used. Even blinkies typically start flashing at a maximum setting of 125% so there is plenty of headroom left when they are blinking.

If you don't believe this, try taking a photo in RAW with 'blown' highlights and reducing the exposure in PP. You will be surprised at how much latitude is built in to your camera, which is not used when taking JPEG. Having a feeling for how much you can overexpose is a good thing.

So there is a lot of scope for 'overexposing' based on what the camera meter believes.

Getting the right exposure (and I don't mean correcting a dark image by winding up brightness with a higher iso, which does nothing for exposure) is important to improve the SNR and reduce noise, and to capture more detail in the whole image, in particular in the shadows. To be safe, and underexpose "to protect the highlights' does the reverse.

Of course if you only use JPEGs, and I accept the convenience of this strategy, you pay the price in reducing potential DR.

Just try it

Tom

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