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Author Topic: questions about exposure blending from one file  (Read 10796 times)
Tyler Mallory
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« Reply #40 on: August 26, 2009, 10:45:36 PM »
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This was posted by another forum member in the Adobe Camera RAW forum here. I've found this to be a very useful technique for making the best use of all of the range captured in a single frame.
The tutorial addresses what you are looking for: managing recovery of tones in a way just a bit more specific than ACR's Recovery tool can manage. Give it a try.

http://imagingpro.wordpress.com/2008/12/03...ingle-raw-file/
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thierrylegros396
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« Reply #41 on: August 27, 2009, 03:08:19 AM »
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Here is a link that works.

SingleRawFile

Thierry
« Last Edit: August 27, 2009, 03:09:02 AM by thierrylegros396 » Logged
Guillermo Luijk
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« Reply #42 on: August 27, 2009, 07:05:03 AM »
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Quote from: MarkDS
Guillermo, what Blend Mode are you using here - is it "Normal" or "Luminosity", because with "Normal" Blend Mode in RGB for curve movements this large one would at least expect saturation shifts.
Normal blending mode. There are no saturation shifts since the curve is a straight line beginning in (0,0), i.e. it's a linear scaling.

Do you experience saturation shifts on your camera when you shoot during 2s instead of shooting during 1s? or when you adjust exposure in the RAW developer? it's the same here, that straight curve just changes exposure so it's perfect for shadow-lifting without altering colour parameters.

Saturation occurs with >1 slope straight curves not passing by (0,0), like in a typical 'S' contrast curve.

Regards.
« Last Edit: August 27, 2009, 07:10:43 AM by GLuijk » Logged

Mark D Segal
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« Reply #43 on: August 27, 2009, 10:34:27 AM »
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Quote from: GLuijk
Normal blending mode. There are no saturation shifts since the curve is a straight line beginning in (0,0), i.e. it's a linear scaling.

Do you experience saturation shifts on your camera when you shoot during 2s instead of shooting during 1s? or when you adjust exposure in the RAW developer? it's the same here, that straight curve just changes exposure so it's perfect for shadow-lifting without altering colour parameters.

Saturation occurs with >1 slope straight curves not passing by (0,0), like in a typical 'S' contrast curve.

Regards.

Over a certain range this is correct as far as I've seen it in PS. Take an image with a skin tone, place a marker on it. Create a Curves Adj Layer in Normal Blend Mode, leave the 0'0 point intact and shift the 255'255 point directly leftward accross the top of the Curves dialog box. If you get what I get, you'll see that H and S remain quite constant over part of the range, but disconnect as you get into way more radical shifts which you probably wouldn't use for that part of the image anyhow. So "yes and no and OK"!

In ACR and LR I cannot measure S independently of H and B because there is only an RGB read-out in those applications - something I wish Adobe would improve upon. However, we have heard from them that they purposely include some saturation change consistently with contrast change because their research demonstrates that most people would not find the result of a pure luminosity change of contrast to look "natural". (Not a big deal as one can dial-in or dial-back any reasonable amount of  saturation change per colour group one wants after shifting the tone curve - but that's another topic.)
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Mark D Segal (formerly MarkDS)
Author: "Scanning Workflows with SilverFast 8....." http://www.luminous-landscape.com/reviews/film/scanning_workflows_with_silverfast_8.shtml
Guillermo Luijk
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« Reply #44 on: August 27, 2009, 11:12:33 AM »
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Quote from: MarkDS
However, we have heard from them that they purposely include some saturation change consistently with contrast change because their research demonstrates that most people would not find the result of a pure luminosity change of contrast to look "natural".
The true is that a change in exposure, i.e. a linear scaling of the RGB values that can for example be achieved with a curve passing by (0,0) as described, is the only possible pure luminosity change.

Anything else: HSB/HSV colour models, Lab, blending modes, etc... are just perceptual models to help us deal with the concepts of luminosity and colour (typically split in these models into hue and saturation, or the ab channels, etc...). E.g. if you push L a lot in Lab mode, the proportions between R, G anB will change to finally end in pure white. Speaking in physical terms, that is not only pushing luminosity but also desaturating, i.e. changing colour. Changing the luminosity of a red lamp consists of producing more red light, not turn the red lamp into a pink lamp and finally white.

So paradoxically, changing luminosity using those tools or modes typically intended to allow a control of luminosity without altering colour, means changing not only luminosity but also colour (of course in a way perceptually as pleasant and natural as possible).

Regards.
« Last Edit: August 27, 2009, 11:18:05 AM by GLuijk » Logged

dimapant
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« Reply #45 on: October 06, 2009, 11:35:45 AM »
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Quote from: GLuijk
It's a question of which software tool or method is more adequate to ease the task. The information contained in the RAW file (or files) is the same for all of them:
- A RAW developer with shadows/highlight and so forth sliders and options
- Two (or more versions) of the same RAW developed at different exposure values and manually blended in PS layers
- A specific tone mapping tool designed to enhance local contrast while reducing global contrast like Photomatix
...

Using 2 (or more) versions of the same RAW file developed at different exposures allows to easily obtain the desired result, and meanwhile there is no other clear winner option this will be one of the methods to use.

Let me show you a test I did some days ago to find out how well Photomatix can blend RAW files with a big exposure gap (4EV): it showed to be a total dissapointment!. A simple algorithm (implemented both in Zero Noise or through this simple tutorial in PS) consisting in selecting the pixels with the highest exposure performs much better than Photomatix's information blending:










If not even a specialized HDR blending software manages to achieve better results than a proper PS blending, why should we forget manual solutions and think a software tool should always be preferred?

Regards

I am striving to get good result with two versions of the same RAW and I installed on my PC your interesting Zero Noise program.

Sorry for this question, which may seems funny; my question is: how can I feed Zero Noise with the files to be blended, as there is no Browse tool to select the files into the different folders of the PC.
Sorry for this, but I could find the way from the page which is coming upon opening the program Zero Noise.

Many thanks for your help and best regards
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