JohnJ
Topic Author
Posts: 1362
Joined: Tue Jun 27, 2000 5:01 am

RAW Digital Exposure Compensation/Quality

Thu Oct 12, 2006 11:24 am

I suspect this subject has been discussed here before, but a search yielded so many hits on different aspects of "digital exposure compensation" that I decided to post a new thread. If there's been a comprehensive discussion of this in the past that someone's aware of I'd appreciate a point in that direction... if not, read on.

I've been through a marathon editing session over the past week or so, finally getting around to the pictures I've taken since July. I shoot in RAW mode, and I have to come clean... I don't often nail the exposure 100%. I use aperture-priority mode on my 300D and it seems to err toward underexposure in all but the brightest sun conditions - and there it tends to overexpose. I find myself adding some brightness to virtually all my shots, but I've been led to believe that bumping up the exposure during editing increases the grain among other problems.

So, my question is this: is there any difference in quality using the RAW converter's digital exposure compensation and contrast selectors vs. using levels, curves and/or brightness/contrast in Photoshop to brighten up a too-dark shot? In other words, for a shot that's too dark, am I better off trying to bump up the exposure in the RAW converter or trying to deal with it in PS? Yes, I know the right answer is to get the exposure right in the camera, but I have no interest in shooting manual at this point in time and the A/V setting is far from perfect.

I use the Canon File Viewer Utility that came with the camera as my RAW editor, as I have an older version of PS that doesn't support RAW format. The main benefit to me in shooting RAW is being able to make these after-the-fact adjustments, but if PS can get me the same benefit with jpegs it doesn't seem RAW is necessary for my purposes. With the 300D using RAW is an exercise in frustration with its 4-shot buffer and eons-long CF card write process.
 
CalgaryBill
Posts: 618
Joined: Thu May 04, 2006 12:27 am

RE: RAW Digital Exposure Compensation/Quality

Thu Oct 12, 2006 2:19 pm

So, my question is this: is there any difference in quality using the RAW converter's digital exposure compensation and contrast selectors vs. using levels, curves and/or brightness/contrast in Photoshop to brighten up a too-dark shot?

I was all eager to say "use a manual light meter, the results will amaze you..." but then you said...

Yes, I know the right answer is to get the exposure right in the camera, but I have no interest in shooting manual at this point in time and the A/V setting is far from perfect.

The reality is that as long as you shoot in some auto exposure setting you will get inconsistent results. Why? The aircraft are all different colours, and the sky is likely changing from cloud to blue sky as you pan, and the plane's size in the viewfinder is changing. Extreme example - dark grey clouds in the background, big white plane on approach, as the plane gets bigger in your viewfinder the camera will underexpose the shots more, and more, and more. So even if you want to use PS to correct your images, every pic is going to require slightly different settings, a royal PITA (sorry Royal!).

You don't say why you "have no interest" but: If it's to save time, getting the exposure right onsite will save you a lot of editing time, and if it's to save money, start by using a grey card and your camera's light meter until you can afford an ambient meter. Either way, it'll work out better than using the camera's guestimeter in A, P or S mode...

And the short answer is: I don't know Canon as I shoot Nikon, but I feel like I have more control and can be more subtle editing in PS, even though I have the full Nikon Capture package. NC handles blown highlights better than PS does, but PS seems (to me) to handle everything else better.

B
 
ChrisH
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RE: RAW Digital Exposure Compensation/Quality

Thu Oct 12, 2006 6:07 pm

The RAW converter will use the full 12 bits available in the file. So to get equal results from photoshop you will need to make sure you work in a 16 Bit tif file.


I use C1 for conversion and it has noise reduction built in, so i tend to do as much as possible in the conversion and then optimally i only have to do selective sharpening and remove dustspots in Photoshop.

Do as much as you can in as early a stage as you can, i guess is the best rule to follow. I shoot AV too and I usually shoot +1/3rd EV. If something gets slightly blown that's easy to fix in conversion. I shoot a Nikon D2x most of the time and it's usually very accurate in it's metering, but all cameras seem programmed to "play it safe". As long as you got the histogram and know how to interpret it, I don't see a big need for an external lightmeter anyway.
what seems to be the officer, problem?
 
JohnJ
Topic Author
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RE: RAW Digital Exposure Compensation/Quality

Thu Oct 12, 2006 11:37 pm

Thanks for othe replies...

Quoting CalgaryBill (Reply 1):
You don't say why you "have no interest" but: If it's to save time, getting the exposure right onsite will save you a lot of editing time, and if it's to save money, start by using a grey card and your camera's light meter until you can afford an ambient meter.

The biggest challenge to me with aviation photography isn't nailing an exposure, but rather trying to stay out of trouble. I shoot at a lot of unfamiliar airports, and rather than stand around in one location I tend to keep on the move and get out of my car only at the very last minute to take a picture. Even on completely public property standing around with a camera near a flight path tends to attract unwanted attention. It's tough enough just getting my camera into shooting position, much less having to deal with a light meter in such situations.

I shoot a lot of railroad pictures as well, and it's a much less challenging subject since the trains move much slower than airplanes, and you can usually get decent angles from 100% public property (not that I haven't had my share of run-ins with police doing railroad photography...). Using any kind of auto mode with rail photography is difficult, as the extremely bright locomotive headlight tends to completely screw the exposure. In these situations I tend to use a "poor man's manual mode", where I shoot the scene I want to capture in A/V mode before the train arrives and view the result to see if it's satisfactory. If it is, I switch to manual and dial the settings in from the test shot. This would be a good place for me to start experimenting with a light meter, I suppose.
 
CalgaryBill
Posts: 618
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RE: RAW Digital Exposure Compensation/Quality

Thu Oct 12, 2006 11:57 pm

I shoot at a lot of unfamiliar airports, and rather than stand around in one location I tend to keep on the move and get out of my car only at the very last minute to take a picture.

It only takes a couple seconds, maybe 15, to nail down the exposure setting. Heck, if you're sitting in your car you can still stick a light meter out the driver's window. Light meters look a lot less dangerous than long, skinny, black tubes like lenses...  Wink

B
 
D L X
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Joined: Thu May 27, 1999 3:30 am

RE: RAW Digital Exposure Compensation/Quality

Fri Oct 13, 2006 12:23 am

Quoting JohnJ (Thread starter):
I know the right answer is to get the exposure right in the camera

Or, you can "shoot to the right."  duck 

Quoting ChrisH (Reply 2):
The RAW converter will use the full 12 bits available in the file.

Another reason to shoot to the right.
 
Avsfan
Posts: 246
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RE: RAW Digital Exposure Compensation/Quality

Fri Oct 13, 2006 1:35 pm

For what it is worth,
I have read in a book (Complete Digital Photography: Third Edition by Ben Long...page 231) and it mentions "that the downside to exposure compensation is that you have no control over how the camera achieves its new exposure. In other words, if you tell it to overexpose by two stops, you don't know if this overexposure will come through changes in aperture or shutter speed. Consequently, you can't predict if the compensation will change your iamge's depth of field (through aperture change) or motion control (through shutter speed change)".

I myself am learning how to shoot aviation photography using the Aperture or Shutter priority modes opposed to the pre-programmed modes as before. I have been experimenting with each. I have noticed various differences when changing the over/under exposure compensation (-0.3 to +0.3) while shooting aircraft.

I can suggest that you perform an experiment to see what the changes are when adjusting the settings. Set your camera on a tripod and shoot numerous photos at a particular subject. While shooting the subject, make sure to try and not move the camera. Then start with a certain f-stop (F8) and take 3 pictures from -0.3 to +0.3 exposure compensation. Then change the f-stop to the next higher one and then retake the pictures with the same exposure compenation settings. Finally take another set of pictures at F10 with the same procedures as before. When you are done, take a look at the results and write down all of the information from the EXIF. The resulting graph/information will probably give you a good idea of what is actually happening. I tried it (without a tripod due to time) and was surprised at what the results were. You will most likely see how certain f-stop/exposure compensation combinations mirror others.

Note: I could be wrong on understanding all of this, but my 2 cents worth.
"Oh I have slipped the surly bonds of Earth...Put out my hand and touched the face of God"
 
Stealthz
Posts: 5546
Joined: Wed Feb 02, 2005 11:43 am

RE: RAW Digital Exposure Compensation/Quality

Fri Oct 13, 2006 3:38 pm

Quoting Avsfan (Reply 6):
Consequently, you can't predict if the compensation will change your iamge's depth of field (through aperture change) or motion control (through shutter speed change)"

I beleive there would be more information in Ben's book and this quote is aliitle out of context.

Exposure compensation.-
Aperture Priority (Av) will vary the shutterspeed according to the compensation selected
Shutter Priority (Tv) will vary the Aperture according to the compensation selected

I believe Ben must have been referring to the Program (P) mode which does alter the shutter speed AND the aperture when setting exposure compensation. Program Mode also has a "Program Shift" capability that will allow you some additional control over those settings.

Regards

Note:These comments and terms are as they relate to Canon equipment

[Edited 2006-10-13 08:40:48]
If your camera sends text messages, that could explain why your photos are rubbish!
 
DC3
Posts: 50
Joined: Fri Sep 03, 2004 9:47 pm

RE: RAW Digital Exposure Compensation/Quality

Fri Oct 13, 2006 3:49 pm

Quoting Avsfan (Reply 6):
"that the downside to exposure compensation is that you have no control over how the camera achieves its new exposure. In other words, if you tell it to overexpose by two stops, you don't know if this overexposure will come through changes in aperture or shutter speed. Consequently, you can't predict if the compensation will change your iamge's depth of field (through aperture change) or motion control (through shutter speed change)".

This may be so if you're set on P for Programme (or Program). Otherwise, of course you do. If you're set on Av then it alters the shutter speed by two stops, If you're set on Tv it alters the aperture by two stops!
 
dc10tim
Posts: 1380
Joined: Mon Jan 03, 2005 12:21 am

RE: RAW Digital Exposure Compensation/Quality

Fri Oct 13, 2006 7:24 pm

John,

I use a 300D and have exactly the same problems with the temperamental evaluative metering mode. In fact, not just the mode, but I'm convinced the meter itself isn't out of this world.

I don't have a light meter, and like yourself shoot in Av mode most of the time. I find I get better results, in terms of image quality shooting in jpeg and underexposing by 1/3 of a stop, then bumping the levels in Photoshop, than I do shooting in RAW and altering the exposure in RAW Shooter. Converting files from RAW to jpeg seems to me to create a lot of unwanted grain and if you mess with the exposure too much, halos around some parts of the image.

Regards,

Tim.
Obviously missing something....
 
Lumix
Posts: 108
Joined: Wed Sep 29, 2004 8:55 pm

RE: RAW Digital Exposure Compensation/Quality

Fri Oct 13, 2006 9:21 pm

Quoting CalgaryBill (Reply 1):
The reality is that as long as you shoot in some auto exposure setting you will get inconsistent results. Why? The aircraft are all different colours, and the sky is likely changing from cloud to blue sky as you pan, and the plane's size in the viewfinder is changing. Extreme example - dark grey clouds in the background, big white plane on approach, as the plane gets bigger in your viewfinder the camera will underexpose the shots more, and more, and more. So even if you want to use PS to correct your images, every pic is going to require slightly different settings, a royal PITA (sorry Royal!).

I've been reading both this thread and the 'Blue sky' thread with interest. The above statement raises a few questions that I have had floating around for a while now.

How does one get the correct (or near enough) exposure in Manual mode on a 30D when trying to shoot landing aicraft in the following secenarios.

1. Blue sky with sun behind.

2. Blue sky with sun behind but covered by a passing cloud.

3. Cloudy sky with sun behind.

4. Cloudy sky but bright with sun covered.

5. Patchy sky with in-and-out sun. Frequently a problem in the UK.

6. Dull, equally frequent in the UK!

I've tried many combinations and have yet to get it just right.

All advice gratefully received.

Thanks,

Lumix.
 
Stealthz
Posts: 5546
Joined: Wed Feb 02, 2005 11:43 am

RE: RAW Digital Exposure Compensation/Quality

Fri Oct 13, 2006 11:08 pm

Lumix...
Practise... and more practise.
In reality 2 & 5 are your problems... and doesn't matter whether you use a grey card or a megadollar(pound or euro whatever) incident light meter they will still be a problem.
All other scenarios you can meter for...

A simple but somewhat trial & error method, on a blue sky day with fluffy white clouds take shots at various settings. when your shots match the sky & clouds you are pretty close.
I am going to be expelled from the JeffM photo school for advocating such rough methods .. but it can work.

Cheers
If your camera sends text messages, that could explain why your photos are rubbish!

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