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07-11-2009, 08:08 AM   #1
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Difficulty with exp. comp

I'm consistently underexposing my shots, particularly if the subject is relatively small in the frame or when focused out to infinity. I often need to check the histogram after each shot, dial in exp. comp -- typically +2/3 -- and retake the shot again. Post processing at home, either RAW or JPEG, be in RawTherapee, Picasa or Silkypix (30day-trial), further adds to brightness adjustment when auto-exposure fix is used, usually another ~+1/2 or so. It seems that the camera histogram doesn't match up with, for example, Silkypix. (Adding that additional +1/2ev directly in camera makes the shot appear overexposed to the camera).

While most of it is my error/ignorance in identifying the scene properly, I'm a little perplexed in the histogram discrepancy between camera and post-processing tools. Is there any loss in detail when extracting/suppressing brightness from RAW/JPEG? I'd think the RAW is good for a couple of EV, but what's the tolerance for JPEG?

BTW, I'm using a k20d, and I have this problem in all modes.

07-11-2009, 02:44 PM   #2
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Hard to say without seeing sample, but based on what you're describing, I'm guessing that when you check the histogram and apply positive compensation as a reuslt, you're trying to 'expose to the right", which results in overexpsoure by traditional standards. The "correct" exposure should have the histogram "averaging" a little left of center. I'm betting you are pushing it to the right because you read that this is better - and it *is*, if the goal is to reduce noise. But the result is a shot that is overexposed by traditional standards, so I'm guessing the auto exposure you say you are using in PP is trying to push that histogram back to the center/left where it normally belongs.
07-13-2009, 09:05 AM   #3
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QuoteOriginally posted by Marc Sabatella Quote
Hard to say without seeing sample, but based on what you're describing, I'm guessing that when you check the histogram and apply positive compensation as a reuslt, you're trying to 'expose to the right", which results in overexpsoure by traditional standards. The "correct" exposure should have the histogram "averaging" a little left of center. I'm betting you are pushing it to the right because you read that this is better - and it *is*, if the goal is to reduce noise. But the result is a shot that is overexposed by traditional standards, so I'm guessing the auto exposure you say you are using in PP is trying to push that histogram back to the center/left where it normally belongs.
Honestly, I'm not aware of any "expose to the right" concept, though I'm curious what it is all about.

Anyway, it's more like I dial in some +EV comp in an attempt to move the histogram towards the middle, followed by the PP tool further increasing the EV and/or the brightness. (Mind you that most of the problem is me not recognizing the need for EV comp in the first place and how much). Here is an example of an original and one with +0.5EV comp. Both get further EV/brightness adjustment in PP, the second one requiring lesser amount.

Last edited by wasim_altaf; 08-06-2009 at 11:09 AM.
07-13-2009, 09:16 AM   #4
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QuoteOriginally posted by wasim_altaf Quote
Honestly, I'm not aware of any "expose to the right" concept, though I'm curious what it is all about.
Google can tell you everything you ever wanted to know about it, but in short, the idea is to deliberately overexpose (but just short of clipping) a picture in order to get the lowest possible noise. Much of the time, you'd then need to darken it again in post processing to get it to look normal.

QuoteQuote:
Here is an example of an original and one with +0.5EV comp. Both get further EV/brightness adjustment in PP, the second one requiring lesser amount.
OK, that sounds normal, then (assuming you want your picture brighter than the one at right). I'm not sure what the problem is, then? Are you saying the picture looks different here than it does on your camera, or that the it looks different before you take it into your PP program than after?

07-13-2009, 10:03 AM   #5
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QuoteOriginally posted by Marc Sabatella Quote
OK, that sounds normal, then (assuming you want your picture brighter than the one at right). I'm not sure what the problem is, then? Are you saying the picture looks different here than it does on your camera, or that the it looks different before you take it into your PP program than after?
I'm still slave to the software, unfortunately, be it in camera or another PP tool. I generally leave things as is from the camera, but I've made the mistake of trying out the 30-day trial version of SilkyPix recently, and I find myself over my head ..

It seems like every PP tool, when its native auto-exposure-fix is applied, tend to like things brighter than in-camera metering/processing. Here is what PP tools did to the original, 0.5EV pic; RawTherapee added another +0.25EV, while SilkyPix added another 0.8EV!

Last edited by wasim_altaf; 08-06-2009 at 11:09 AM.
07-13-2009, 10:14 AM   #6
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I'd guess that the "auto" setting in your PP software is adjusting the levels such that the brightest thin in the picture is pure white, the darkest thing pure black, and spreading out the histogram from there. Depending on the original image, that will result in image with brighter highlights, darker shadows, or both, than what a standard exposure would give.
07-13-2009, 02:21 PM   #7
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Also, it might just be your computer monitor?
Computer monitors need to be calibrated to get the really right results as per your camera or the software.
So, if your monitor was set to a low brightness, the pictures might come out dark on the computer or vice versa.
The shot you took might not look right on your computer but might look right on somebody elses computer too.
This is just another angle to look at and not just the camera settings or the PP software.
The right guide is to go by the histogram as it shows you (like a graph) how it was exposed and not how it looks on your computer or LCD viewfinder.
07-13-2009, 09:28 PM   #8
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QuoteOriginally posted by wasim_altaf Quote
I'm still slave to the software, unfortunately, be it in camera or another PP tool. I generally leave things as is from the camera, but I've made the mistake of trying out the 30-day trial version of SilkyPix recently, and I find myself over my head ..

It seems like every PP tool, when its native auto-exposure-fix is applied, tend to like things brighter than in-camera metering/processing. Here is what PP tools did to the original, 0.5EV pic; RawTherapee added another +0.25EV, while SilkyPix added another 0.8EV!
PP software and your camera's meter are not as smart as you. They don't know your subject or exactly how you want to render it. Their numbers are just suggestions that avoid typical issues, not "the perfect exposure that you must apply to this image". You might have different ideas.

An example: my wife and I are in a coffee shop with big windows on a bright morning. I get out my camera and take a few shots of her with the windows in the background. The camera's meter is going to try to keep the background outside view from being too bright. PP software might try to underexpose even more. Relying on these tools means my actual subject is a featureless silhouette against a well-exposed window view, not what I want.

That's why you have exposure compensation available. It's not there to make the histogram shape look right or make the camera happy with the exposure, especially if those settings create a bad image. It's to create a better image based on your advance knowledge of the subject and conditions.

Much shorter version of the above: You don't have to be a slave to any of those tools, if they are not producing the image you want.

07-15-2009, 08:34 AM   #9
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QuoteOriginally posted by Marc Sabatella Quote
I'd guess that the "auto" setting in your PP software is adjusting the levels such that the brightest thin in the picture is pure white, the darkest thing pure black, and spreading out the histogram from there. Depending on the original image, that will result in image with brighter highlights, darker shadows, or both, than what a standard exposure would give.
You are probably right. Each tool has its own name for it -- SilkyPix calls it Exposure Comp, Pentax PhotoLab calls it Sensitivity Adjustment, RawTherapee calls it Brightness Adjustment -- in addition to highlight and black level adjustment. All of those are getting applied in some manner with this auto-image fix, so it's not directly analogous to in-camera EV comp.
07-15-2009, 09:51 AM   #10
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Adjust your photos to the look that YOU want. In your examples, I kind of prefer the first exposure ( the slightly "darker" one). Also, shooting around water with a white boat and buildings in the background is not an easy scene for your cameras meter to handle and it will adjust the exposure to not overexpose the highlights and will look somewhat underexposed. The same thing happens in snow. You will usually have to do some adjusting in PP. Boosting the EV made the sails and buildings more white and less gray but the sky looses a little. I've found that the auto fix features of most editing programs I have used rarely give me what I want. It takes more time but I prefer to just adjust the areas that I think need it.
07-16-2009, 11:37 AM   #11
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This is the folly of trusting in-camera meters. As another user above pointed out, they are not smart: they work using pre-programmed pattern averages (in the best case scenarios) or simply averaging the entire scene to 18% grey (in the worst scenario). How do you avoid this? By realizing that you are smarter than the equipment at deciding how a scene should be exposed. To do this, you need to buy a light meter with incident (all have this) and spot (not all have this) features. Additionally, if your camera has a built-in spot meter, use that and save yourself some bucks. Meter the scene using the Zone System (look it up online, or purchase The Negative by A. Adams), and set the exposure manually.

Just a reminder, if you're using an external light meter, you should be adding approximately 1/3 to 1/2 stop to the exposure to compensate for light lost during its transmission through the lens.

Last edited by mischivo; 07-16-2009 at 11:46 AM.
07-16-2009, 12:42 PM   #12
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If I were shooting that white ship, I would measure the exposure of the blue sky above it, lock it or take note of the f/stop value and you got the correct exposure, e. g., whites are white, not gray. Don't be fooled by camera readings, they are often wrong!

BTW, that's a Portuguese vessel, a school ship by the name of "Sagres"!
07-20-2009, 08:42 AM   #13
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QuoteOriginally posted by mischivo Quote
Additionally, if your camera has a built-in spot meter, use that and save yourself some bucks. Meter the scene using the Zone System (look it up online, or purchase The Negative by A. Adams), and set the exposure manually.
K20d has a spot-meter setting, though I haven't used it much yet.

Couldn't help checking out your website. Liked those UofT front-campus pics, especially that night shot of a man on the Con-Hall bench. That used to be my smoking corner.. I remember spending many hours at the UC and Sig Sam libraries. I should make an effort to visit those quarters next time I'm in Toronto.
07-20-2009, 08:54 AM   #14
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QuoteOriginally posted by Manel Brand Quote
BTW, that's a Portuguese vessel, a school ship by the name of "Sagres"!
Yes, it is. Tall ships from around the world, of all sizes and shapes, came round Boston a couple of weeks ago, before heading out to Halifax, Canada, I believe. I didn't have the time to wait in line to board any of the ships. But one of my colleagues did wait it out and took a guided tour of the Sagres. A light refreshment was served and, presumably, they had an unlimited supply of Portuguese beer (canned), also named "Sagres."
07-21-2009, 09:26 PM   #15
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QuoteOriginally posted by wasim_altaf Quote
K20d has a spot-meter setting, though I haven't used it much yet.

Couldn't help checking out your website. Liked those UofT front-campus pics, especially that night shot of a man on the Con-Hall bench. That used to be my smoking corner.. I remember spending many hours at the UC and Sig Sam libraries. I should make an effort to visit those quarters next time I'm in Toronto.
That's just Gooshin attempting to look natural.

Last edited by mischivo; 07-22-2009 at 09:19 AM.
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