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Author Topic: Underexposure or Overexposure?  (Read 19796 times)
samosa
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« on: January 04, 2007, 03:23:48 PM »
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Michael Reichmann, in his "Understanding DSLR Workflow" article on this site, states:
"Digital has a remarkable ability to extract detail from the shadows. When shooting digital, always ere (if you have to) on the side of underexposure."

whereas Bruce Fraser - another highly respected digital processing expert states (in Real World Camera Raw):

"correct exposure in the digital realm means keeping the highlights as close to blowing out, without actually doing so, as possible.....it's better to err on the side of slight overexposure".

So who is right?

I have to say the explanation given by Bruce Fraser seems quite convincing - its too long to go into here but basically there are more levels of data at the brighter end of the scale, so if you subsequently have to "stretch" the data in levels or curves then you'll get more data to play with.

Any thoughts?
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bjanes
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« Reply #1 on: January 04, 2007, 04:27:17 PM »
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Michael Reichmann, in his "Understanding DSLR Workflow" article on this site, states:
"Digital has a remarkable ability to extract detail from the shadows. When shooting digital, always ere (if you have to) on the side of underexposure."

whereas Bruce Fraser - another highly respected digital processing expert states (in Real World Camera Raw):

"correct exposure in the digital realm means keeping the highlights as close to blowing out, without actually doing so, as possible.....it's better to err on the side of slight overexposure".

So who is right?

I have to say the explanation given by Bruce Fraser seems quite convincing - its too long to go into here but basically there are more levels of data at the brighter end of the scale, so if you subsequently have to "stretch" the data in levels or curves then you'll get more data to play with.

Any thoughts?
[a href=\"index.php?act=findpost&pid=93725\"][{POST_SNAPBACK}][/a]


Sometime back there was an extended thread in the Adobe Camera Raw forum where I expressed Michael's view and Bruce disagreed. It is true that half the information in a linear digital file is in the brightest f/stop and under-exposure does not make use of these tones. Bruce's point was that it is safer to darken a digital image because the highlights are information rich is well taken. However, one could argue that the eye can not make use of all 4096 tones of a digital raw file.

Many digital cameras allow some headroom in the highlights, and these can be recovered with Adobe Camera Raw and other raw converters, up to half a stop or so according to Bruce and depending on the camera. If all three color channels are not clipped, some degree of recovery is possible, although a color shift may occur. However, totally clipped highlights are lost. Under-exposure loses the above tones and also is associated with more noise.

One can make a case for either viewpoint.

Bill
« Last Edit: January 04, 2007, 08:23:21 PM by bjanes » Logged
Eric Myrvaagnes
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« Reply #2 on: January 04, 2007, 04:45:13 PM »
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Michael Reichmann, in his "Understanding DSLR Workflow" article on this site, states:
"Digital has a remarkable ability to extract detail from the shadows. When shooting digital, always ere (if you have to) on the side of underexposure."

whereas Bruce Fraser - another highly respected digital processing expert states (in Real World Camera Raw):

"correct exposure in the digital realm means keeping the highlights as close to blowing out, without actually doing so, as possible.....it's better to err on the side of slight overexposure".

So who is right?

I have to say the explanation given by Bruce Fraser seems quite convincing - its too long to go into here but basically there are more levels of data at the brighter end of the scale, so if you subsequently have to "stretch" the data in levels or curves then you'll get more data to play with.

Any thoughts?
[{POST_SNAPBACK}][/a]
Check out Michael's other tutorial on "Expose (to the) Right): [a href=\"http://www.luminous-landscape.com/tutorials/expose-right.shtml]http://www.luminous-landscape.com/tutorial...ose-right.shtml[/url] .
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howiesmith
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« Reply #3 on: January 04, 2007, 04:46:07 PM »
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One can make a case for either viewpoint.

[a href=\"index.php?act=findpost&pid=93743\"][{POST_SNAPBACK}][/a]

Seems you can have your cake and eat it too.  Ain't digital just grand.

Does Bruce's position mean "expose to the right?'
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John Sheehy
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« Reply #4 on: January 04, 2007, 04:48:48 PM »
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One can make a case for either viewpoint.

[a href=\"index.php?act=findpost&pid=93743\"][{POST_SNAPBACK}][/a]

What really matter is what tone you want to record accurately.  If you want them all, then you have to record just short of clipping.  If the shadows are your main interest, then it might be advantageous to blow the white clouds, or white shirts, etc.

If you have to gamble, and you want the highlights, then under-exposing, as Michael suggests, will be the safest.

The right answer, most of the time, is that the answer depends on the situation.
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John Sheehy
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« Reply #5 on: January 04, 2007, 04:53:05 PM »
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I wrote:
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If you have to gamble, and you want the highlights, then under-exposing, as Michael suggests, will be the safest.

[a href=\"index.php?act=findpost&pid=93750\"][{POST_SNAPBACK}][/a]

Some day, we may have cameras in which under-exposing by a stop or two is not a big noise problem.  Right now, there is far too much read noise for even low ISOs to have clean shadows.  If my Canons had an ISO 100 that was 16 bits, and the least significant 12 of them were as clean as its ISO 1600, I'd be very pleased.
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howiesmith
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« Reply #6 on: January 04, 2007, 05:02:07 PM »
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What really matter is what tone you want to record accurately.  If you want them all, then you have to record just short of clipping.  If the shadows are your main interest, then it might be advantageous to blow the white clouds, or white shirts, etc.

If you have to gamble, and you want the highlights, then under-exposing, as Michael suggests, will be the safest.

The right answer, most of the time, is that the answer depends on the situation.
[a href=\"index.php?act=findpost&pid=93750\"][{POST_SNAPBACK}][/a]

Sounds like slide film.  Expose right (correctly).
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Jonathan Ratzlaff
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« Reply #7 on: January 04, 2007, 06:46:26 PM »
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It is just like shooting slide film except that more shadow detail is available to you.  The main rule is to know your sensor like you know film.  Once you are familiar with the way the sensor responds you don't have to worry about it as you will know what the exposure is going to look like before you take the picture.
Any exposure where highlight detail is lost beyond recovery is undesirable.  When you look at bright areas you are used to seeing detail there and a lack thereof (blown highlights) is disturbing.  It is more natural to see little or no detail in very dark portions of the image because you are faced with this everytime you go out in the dark; there are areas where you can't see any detail at all
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howiesmith
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« Reply #8 on: January 04, 2007, 07:20:24 PM »
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It is just like shooting slide film except that more shadow detail is available to you. The main rule is to know your sensor like you know film. [a href=\"index.php?act=findpost&pid=93768\"][{POST_SNAPBACK}][/a]
It still sounds like slide film (another positive) but with different dynamic range.  I also understand digital is linear and film is not.
« Last Edit: January 04, 2007, 07:21:41 PM by howiesmith » Logged
John Sheehy
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« Reply #9 on: January 04, 2007, 08:12:36 PM »
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Sounds like slide film.  Expose right (correctly).
[a href=\"index.php?act=findpost&pid=93753\"][{POST_SNAPBACK}][/a]

"Expose correctly" is a meaningless concept.  The optimal exposure depends on what tonal ranges are most important to you, the camera in question, and your workflow.
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howiesmith
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« Reply #10 on: January 05, 2007, 04:25:49 AM »
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The optimal exposure depends on what tonal ranges are most important to you, the camera in question, and your workflow.
[a href=\"index.php?act=findpost&pid=93780\"][{POST_SNAPBACK}][/a]

That's right.  "Expose correctly"
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ErikKaffehr
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« Reply #11 on: January 05, 2007, 05:29:05 AM »
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Hi,

I think that we need to expose for highlight, the shadows are more often than not not a big deal. Best way is probably to use tripod and take three or more exposures and combine with HDR technique.

For optimum shadows we would need to use low ISO.


Best regards

Erik

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That's right.  "Expose correctly"
[a href=\"index.php?act=findpost&pid=93825\"][{POST_SNAPBACK}][/a]
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John Sheehy
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« Reply #12 on: January 05, 2007, 07:45:07 AM »
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That's right.  "Expose correctly"
[a href=\"index.php?act=findpost&pid=93825\"][{POST_SNAPBACK}][/a]

I don't think so.  "Expose correctly" connotes that any give scene has a single exposure level for a given ISO, for all cameras and workflows; that's how 99% of the people will hear it.
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howiesmith
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« Reply #13 on: January 05, 2007, 08:02:14 AM »
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I don't think so.  "Expose correctly" connotes that any give scene has a single exposure level for a given ISO, for all cameras and workflows; that's how 99% of the people will hear it.
[a href=\"index.php?act=findpost&pid=93851\"][{POST_SNAPBACK}][/a]

Well John, I guess you and the rest of the "99%" can't be wrong.  

Because I don't use every ISO, all cameras or workflows, I have a correct exposure for me.
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Eric Myrvaagnes
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« Reply #14 on: January 05, 2007, 08:46:46 AM »
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I don't think so.  "Expose correctly" connotes that any give scene has a single exposure level for a given ISO, for all cameras and workflows; that's how 99% of the people will hear it.
[a href=\"index.php?act=findpost&pid=93851\"][{POST_SNAPBACK}][/a]
I'm with Howie on this one. For anyone but a rank beginner, it should be obvious that "expose correctly" means that you must consider
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what tonal ranges are most important to you, the camera in question, and your workflow.

It may happen that for most (or, for some photographers even all) of your photographs require capturing all available highlight detail. But most of us understand that we must make tradeoffs some of the time. To me, when I "expose correctly", it means I have weighed all of the trade-offs and chosen the exposure that best fits my personal vision.
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feppe
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Oh this shows up in here!


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« Reply #15 on: January 05, 2007, 08:58:11 AM »
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A while back (months?)  someone posted an image composed of vertical strips of varying exposures, each corrected to match the ideal.  I can't find it now, but I remember something like 1-2 stops off ideal exposure showed considerable noise.

It was a great example - a landscape at sunset/sunrise - maybe illustrating blended exposures...
[{POST_SNAPBACK}][/a]

I believe you mean the one Timothy Farrar posted in a related thread here:

[a href=\"http://luminous-landscape.com/forum/index.php?showtopic=13084&hl=]http://luminous-landscape.com/forum/index....topic=13084&hl=[/url]
« Last Edit: January 05, 2007, 09:03:58 AM by feppe » Logged

bjanes
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« Reply #16 on: January 05, 2007, 02:13:33 PM »
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Seems you can have your cake and eat it too.  Ain't digital just grand.

Does Bruce's position mean "expose to the right?'
[a href=\"index.php?act=findpost&pid=93749\"][{POST_SNAPBACK}][/a]

Yes, I think that is what he recommended. He once stated that proper exposure was not blowing the highlights you wished to preserve, and this involves ETTR.

Bill
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djgarcia
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« Reply #17 on: January 05, 2007, 03:35:51 PM »
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I would imagine that's why Bruce said "expose to the right" and not "overexpose to the right" ...
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John Sheehy
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« Reply #18 on: January 05, 2007, 05:11:19 PM »
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I would imagine that's why Bruce said "expose to the right" and not "overexpose to the right" ...
[a href=\"index.php?act=findpost&pid=93943\"][{POST_SNAPBACK}][/a]

Unfortunately, camera manufacturers don't seem to care if we know where the right really ends.  They supply absolutely such information, and their software often ignores extreme RAW highlights.  Only the lowest ISO on a camera stands a chance of having non-linear extreme highlights; and even so, the camera could be profiled for a proper translation, but they are not.  We live in a dark, sloppy age of RAW exposure.
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samosa
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« Reply #19 on: January 06, 2007, 12:15:25 PM »
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Thanks to all for your comments. In particular thanks to Eric M for pointing out Michael's other article on the subject ("Expose (to the) Right): http://www.luminous-landscape.com/tutorial...ose-right.shtml )
in which he clearly comes around to the same argument used by Bruce Fraser.

To be fair to Michael I think the article which suggested biasing towards underexposure was written before he had spoken to Thomas Knoll about bias of levels towards the highlights.

So there we have it. The experts agree, as does the science: you should, if anything, bias towards overexposure in RAW without clippling the highlights (although some highlight recovery my be possible in the RAW converter).
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