An exposure question - correct tone v retaining detail in the highlights.

[corbybhoy]

hi, i hope that you can help me improve my exposure understanding by answering the following question.

I get that when photographing a snowy or high key scene that I need to overexpose to ensure that I place the white snow etc as white and not mid grey. However, my Camera has a narrow dynamic range in the highlights so a 1- 2 stop over exposure results in horrible clipping. Is there therefore a balancing act to be done here between rendering white (snow) as white and maintaining the details without clipping?

If so I assume the detail comes first and the tone replication a close second? Or am I totally of track here?



Hope you can advise,
Many thanks Gary

[PhotomanJohn]

Gary - I think you have something backwards here. What you don't want to do is overexpose the highlights so that they become what is called saturated and you loose all detail. What you want is an exposure that is just below where clipping begins otherwise the highlights will turn into white blobs. You might be confused by a method of setting the exposure where you meter on the highlights only and then increase the exposure about 1.7 to 2 stops to make then white. This only works when you are spot metering on only the white highlights and not the scene in general. This works because if you used the exposure you measured on the highlights only then they would turn out grey in the final photo. It sounds like your exposure measurement is an average of the scene and not just the highlights.

Is this making any sense? If not, give us some more specifics of exactly how you are measuring the exposure and applying a correction.

John

[Colin Southern]

Hi Gary,

Dynamic range is the range between "any brighter and you'll lose detail" and "any darker and you won't be able to seperate the signal from the noise" - so "my Camera has a narrow dynamic range in the highlights" doesn't actually make a lot of sense to be honest.

Most modern cameras are capturing around about 12 stops of dynamic range (assuming that you're shooting RAW, as you should be!) - and we typically only use about 6 of these when displaying on our monitors, and only 4 when printing -- so chances are you're capturing a lot more detail than you need (or realise) -- you just can't see it without compressing it.

To answer the question though, most cameras have highlight alert functions that warn you if you're starting to lose highlight detail (the affected areas flash) - if that's on - and you're shooting a low-contrast & bright scene like snow, then you'll typically need to increas the exposure by about 2 stops - but - if there is already some contrast in the scene then the camera metering may well already have compensated a little bit, so you may only need to apply EC of around a stop or so.

In short though, under-exposure is better than over-exposure with digital, and if you shoot RAW - even with a two stop under-exposure - you'll still have more than enough safety margin.

What make/model camera do you have by the way?

[PhotomanJohn]

As usual, Colin did a better job of explaining it.

John

[Colin Southern]

As usual, Colin did a better job of explaining it.

John

Not really

[Geoff F]

Gary, just one slight addition to Colin's detailed reply. Remember that with digital editing it is quite easy to convert grey snow into white snow. But there is no point in photographing perfectly white snow without any fine details.

So when in doubt, I always prefer to err slightly on the side of under exposure, as Colin suggested..