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exposure question
A digital image that is underexposed views as being dark. If this was a negative is it correct that the negative would be thin / light? This being the case would an over exposed digital image contain more detail than a underexposed? In the case of a white building would I get meor detail with a over expposed setting?Thanks, Airpix..

Comments (8)

No..

In digital, overexposure makes the informtion go away. Underexposed, at least to a small extent, allows you to brighten the picture, and bring up some detail..

BAK..

Comment #1

See this exhaustive thread about exposure:.

Http://photocamel.com/...m/photography-talk/28254-understanding-exposure.html.

I found it VERY helpful..

John ford wrote:.

A digital image that is underexposed views as being dark. If this wasa negative is it correct that the negative would be thin / light?This being the case would an over exposed digital image contain moredetail than a underexposed? In the case of a white building would Iget meor detail with a over expposed setting?Thanks, Airpix..

Comment #2

John ford wrote:.

A digital image that is underexposed views as being dark. If this wasa negative is it correct that the negative would be thin / light?.

Digital camera images are more similar to a slide / transparency. An underexposed transparency is dark/dense..

In the case of digital images, detail can sometimes be recovered from dark shadow areas, but at the expense of increased noise. In severe underexposure, no detail at all is retrieved from the darkest areas, just random and meaningless noise..

When you overexpose a transparency film, the result is totally clear film (in the highlights) containing no useful information at all..

Digital is similar, detail which is lost in over-exposed highlights cannot be recovered. May be a slight over-simplification, but it's a reasonable description.Regards,Peter..

Comment #3

You can get more information by over-exposing, if you don't clip the highlights. Clipping the highlights means you are saturating the sensor with data, and it can't read any higher. Once you start clipping the highlights, you start losing data..

This article might explain it better:.

Http://forums.dpreview.com/...parent=24889512&thread=24889512&quote=0.

Of course if you overexpose for more information, make sure you use raw and use a raw viewers digital exposure compensation to correct the exposure...

Comment #4

You get more information, i.e. less noise. Whether that translates to more detail depends on the picture...

Comment #5

I find that exposure determination with digital works very differently to film..

With film, you can measure the light or the shadow and adjust (with an eye to the "Zone System") accordingly..

With digital, you tend to get what you see (on the LCD)..

Attempts at second-guessing the AE settings by over-riding, using exposure compensation, tend to make a hash of the image (washed out or too dark)..

I think, the reason for this may be that the digital camera already "averages" the scene and already makes the "best" compromise between highlights and shadows..

In anycase, I find the camera does a very good job in "auto", even under very difficult lighting conditions...

Comment #6

AGree..

Sherwoodpete wrote:.

John ford wrote:.

A digital image that is underexposed views as being dark. If this wasa negative is it correct that the negative would be thin / light?.

Digital camera images are more similar to a slide / transparency. Anunderexposed transparency is dark/dense.In the case of digital images, detail can sometimes be recovered fromdark shadow areas, but at the expense of increased noise. In severeunderexposure, no detail at all is retrieved from the darkest areas,just random and meaningless noise.When you overexpose a transparency film, the result is totally clearfilm (in the highlights) containing no useful information at all.Digital is similar, detail which is lost in over-exposed highlightscannot be recovered. May be a slight over-simplification, but it's areasonable description.Regards,Peter..

Comment #7

Each pixel produces a voltage proportional to the amount of light it sees. There is a maximum and minimum voltage and anything in between is a possible voltage. Unless you're shooting raw this voltage range is divided up into 256 "buckets" corresponding to a density or darkness level in your photograph. When you overexpose your photo there are no voltages in the lower voltage range so none of those buckets are used. The lighter areas would have the maximum voltage (pure white) so you would have no detail in the highlights. When you underexpose the opposite occurs - all the darkest areas get put in the zero bucket (black) and the lightest buckets don't get used.



It's possible to shoot two images of the same subject and expose one for the highlights and one for the shadows, then combine them afterwards, thereby effectively creating more buckets..

If you are shooting raw substitute 4096 for 256 and the same concepts apply..

The word voltage above can be substituted with any other physical quantity, such as resistance and the same ideas apply...

Comment #8

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This question was taken from a support group/message board and re-posted here so others can learn from it.

 

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