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Author Topic: underexposure compensation  (Read 7483 times)
abaazov
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« on: September 03, 2005, 10:19:52 AM »
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anyone wanna beat me with a stick?? whats the price?
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abaazov
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« Reply #1 on: September 04, 2005, 07:09:06 PM »
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ok bob get in line, but you gotta bring your own stick!
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russell a
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« Reply #2 on: September 05, 2005, 10:19:24 AM »
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Let he who has never committed this sin strike the first blow.  Be honest, now.  Smiley
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digitaldog
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« Reply #3 on: September 05, 2005, 12:22:47 PM »
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Quote from: bobrobert,Sep. 05 2005,14:11
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You obviously haven't read Dan's book When you use the false profiles you are assigning the profile It is accessed from Mode > Assign profile Michael Kieran in PS Color Correction covers the same ground It is as I previously stated worth learning
I’ve read ALL of Dan’s books (and we are in agreement in some areas and total disagreement in others, notably his views on high bit editing).

When you assign the profile, you do not alter the numbers. That’s good. It’s fast and it can work. However, when you eventually convert that data to any other color space (which you need to do to output the file), the “corrections” will be applied. As I said, there’s no free lunch here. Do either the corrections or the “False Profile’ (dumb name, it’s not false) on high bit data to minimize the data loss. But there IS data loss unless you simply keep the images in the original color space with this new profile description.
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Andrew Rodney
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abaazov
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« Reply #4 on: September 05, 2005, 03:20:26 PM »
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i guess you guys are familiar with bruce fraser's real world camera raw. he gives a good example in chapter 5 of recovering an underexposed image. i've read and re-read the example a few times, and if i understand correctly, all i can do is make sure there is no clipping and no posterization and finally increase luminance smoothing as much as needed. really all i do is what i usually do in terms of workflow, with the only noticeable difference in his example being that he adjusts white balance after making the tonal adjustments, not before. obviously the data that was lost because of the underexposure is simply lost, nothing can be done to retrieve it. i guess minor underexposure is ok, sometimes even desired, but severe underexposure like in my case is hard to correct. i have the same pictures taken with the right exposure and underexposed 2 stops, and it's actually a good exercise trying to see how close to the first i can come with the second. but this "noise" thing keeps coming back! this lesson has been learned!


p.s.: russell thanks for making me feel a little better. stupidity is always more bearable the greater the numbers! now i think my bamboo kon tiki is ready.....

amnon
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abaazov
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« Reply #5 on: September 05, 2005, 08:29:21 PM »
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jonathan do you do anything differently in the first noise reduction when you know you will do noise reduction twice on the same picture? also, i always run focus magic before i do anything (after conversion of course), do you suggest noise reduction before focus correction?
thanks....
amnon
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Jonathan Wienke
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« Reply #6 on: September 10, 2005, 10:59:40 AM »
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This is good advice, but remember that artitrary edits in the RAW converter will invalidate previously made noise profiles. Positive expsoure correction strongly affects noise.
I'm well aware of this; shutter speed affects noise almost as much as exposure compensation, which is why I generally reprofile for each image for best results. But I do have a collection of saved profiles I use if an image doesn't have any areas suitable for reprofiling.
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abaazov
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« Reply #7 on: September 03, 2005, 08:50:47 AM »
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hi guys. i just came back from a safari in southern africa. unfortunately the first two days there all the pictures i took were underexposed by 2 stops. the first day i wanted to take a picture and set the exposure compensation on my 20d to -2 and forgot about it for two days. i have looked at some of the pictures and simply by increasing the exposure in camera raw most of the pictures come out quite fine actually. i am just wondering if there is some kind of technique that can be used for these situations, when you know the picture is underexposed, or simply do you just increase the exposure as much as you can or need in camera raw?

thanks...
amnon
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Jonathan Wienke
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« Reply #8 on: September 03, 2005, 09:44:56 AM »
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You're screwed, more or less. You can use exposure compensation (your best option if you shot RAW) but you're going to pay a significant penalty in additional noise. You should pay someone to beat you with a stick unmercifully.
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bobrobert
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« Reply #9 on: September 04, 2005, 08:26:31 AM »
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False profiles in PS will rescue an underexposed image Dan Margulis in Professional PS goes into the topic in detail On the disc that comes with it he provides the profiles You can create them yourself but it is fiddly Basically windows is 2.2 gamma. 1.0 gamma and 1.4 gamma and 1.8 gamma can be used depending on the amount of underexposure It it is worth the bother tracking down the information to learn this technique
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boku
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« Reply #10 on: September 04, 2005, 11:09:19 AM »
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hi guys. i just came back from a safari in southern africa. unfortunately the first two days there all the pictures i took were underexposed by 2 stops. the first day i wanted to take a picture and set the exposure compensation on my 20d to -2 and forgot about it for two days. i have looked at some of the pictures and simply by increasing the exposure in camera raw most of the pictures come out quite fine actually. i am just wondering if there is some kind of technique that can be used for these situations, when you know the picture is underexposed, or simply do you just increase the exposure as much as you can or need in camera raw?

thanks...
amnon
You mean you never looked at the LCD after taking the pictures for 2 days? Never looked at the histogram? Really?
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Bob Kulon

Oh, one more thing...
Play it Straight and Play it True, my Brother.
61Dynamic
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« Reply #11 on: September 04, 2005, 10:01:06 PM »
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You're screwed, more or less. You can use exposure compensation (your best option if you shot RAW) but you're going to pay a significant penalty in additional noise. You should pay someone to beat you with a stick unmercifully.
Not to mention a loss of detail as well.


Any preference of stick? Wicker or perhaps bamboo?
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abaazov
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« Reply #12 on: September 05, 2005, 07:31:30 AM »
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how about bamboo....maybe after you're done i can make a raft with the sticks and sail away....................
but seriously guys this is the first time it's happened to me. i almost always check my histogram (thats actually how i found my error on the second day). simply the reason it happened is i was enjoying the safari quite alot, and photography took a backseat, i didn't want to miss anything, so i didn't bother checking the pictures i was taking. if i checked every single picture i took after i took it i probably would have missed alot. that being said, i still need to be beaten unmercifully, there are a few pictures that would have should have could have been beautiful.....oh well, live and learn. the good news is i had another seven days after that, so i was able to photograph to my heart's content overall.

amnon
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boku
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« Reply #13 on: September 05, 2005, 10:46:48 AM »
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Let he who has never committed this sin strike the first blow.  Be honest, now.  
I only sinned this sin for 10 minutes. Once.      

While we're confessing...

On my first shoot after I acquired a 300D, I forgot that the ISO was still set at 1600 from taking some indoor test shots the night before. I no longer flog myself after I see that I was victimized by Canon's stupid refusal to put the ISO in the viewfinder. I graduated to a 10D, then a 20D, still no ISO indicator in the viewfinder. Next up is a 5D. Still no ISO indicator in the viewfinder.
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Bob Kulon

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Play it Straight and Play it True, my Brother.
digitaldog
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« Reply #14 on: September 05, 2005, 12:28:24 PM »
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I should point out I’ve had a tutorial on my web site for years that discuss using the Color Settings/Edit RGB to build simple profile edits, primarily for digital capture. If you shoot and have the RAW encoded into sRGB or Adobe RGB (1998) in camera, you might want to tweak this without altering the data and this technique can work pretty well.

I also use a Profile Editor (Custom Color ICC from Kodak) to build edits in working space’s ala Joe Holms EktaSpace tweaks. I’m not at all opposed to this process but you have to understand the benefits (mostly speed) and the downsides (it’s simply not lossless after conversion).

It’s a heck of a lot faster to use an AppleScript or Automator if you’re on a Mac to batch assign a modified working space profile to 1000 images compared to opening each in Photoshop and either using the Assign Profile or actually edit the pixels. That’s the main advantage of using modified profiles.
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Andrew Rodney
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PeterLange
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« Reply #15 on: September 05, 2005, 02:59:18 PM »
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I suggest to make a difference between exposure and gamma.  The digital representation of exposure +/- EV is the RGB-Levels’-highlights slider – in whatever gamma space; also called Exposure slider in ACR.  The latter has a competitive edge because it is applied onto the data before the tone curve from Brightness&Contrast comes into play.

Assignment of false profiles can introduce akin of tone curve (e.g. +/- gamma), but won’t effect exposure.  Such assignments make much more sense if we talk about Chroma Variants.

Peter

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bjanes
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« Reply #16 on: September 10, 2005, 08:01:05 AM »
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Get the image as close as possible to the intended finished product in the RAW converter, convert in 16-bit mode, and then immediately run a Neat Image or Noise Ninja pass on the file to deal with the noise.

This is good advice, but remember that artitrary edits in the RAW converter will invalidate previously made noise profiles. Positive expsoure correction strongly affects noise.

You can have NN or NI autoprofile each image after adjustments, but sometimes the image lacks sufficiently large areas or representative tones without detail and premade profiles will work better.

One way around this problem is to make a number of noise profiles for varying amounts of exposure compensation--say +0.5EV, +1EV, +1.5EV, +2EV and use these as needed. NN is capable of matching these profiles automatically to exposure corrections made in Camera Raw
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Jonathan Wienke
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« Reply #17 on: September 05, 2005, 11:43:55 AM »
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BobRobert, Andrew Rodney is one of the foremost experts in the area of color management, and you obviously haven't read and comprehended his post. Using weird profiles with non-standard gamma only delays the inevitable; when you convert from the assigned weird profile to a standard editing space or print the image (printing inevitably requires converting the RGB values from the document profile to the printer profile) you lose exactly what the weird profile assignment is trying to avoid. There is zero advantage to the technique you recommend; you're far better off converting the image to a standard editing space with a standard gamma (1.8-2.2) and dealing with the noise and quantization issues there.
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Jonathan Wienke
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« Reply #18 on: September 05, 2005, 04:18:22 PM »
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i have the same pictures taken with the right exposure and underexposed 2 stops, and it's actually a good exercise trying to see how close to the first i can come with the second. but this "noise" thing keeps coming back!
Get the image as close as possible to the intended finished product in the RAW converter, convert in 16-bit mode, and then immediately run a Neat Image or Noise Ninja pass on the file to deal with the noise. That will minimize the noise problem; then color correct & sharpen. You may want to run a second lighter noise reduction pass after sharpening.
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Peter McLennan
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« Reply #19 on: September 05, 2005, 05:36:47 PM »
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I'm both dismayed and pleased that Canon cameras have this characteristic, too.  Namely that exposure compensation is "sticky".   My D70 does this and it's a PITA.

IMHO, the exposure compensation should return to zero with a camera shutdown and reboot cycle.  Or at least make that option available.

Verily, I, too have sinned.
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