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Author Topic: Shouldn't saving 16bit Tiff preserve DR like a raw file?  (Read 8288 times)
Marshallarts
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« Reply #20 on: March 03, 2010, 05:16:45 PM »
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Thanks for all the incredibly detailed responses!  It's going to take me awhile to digest all of this.  And thank you for kindly providing links, I look forward to referencing them time and time again in the future.  

I found another quote that helped me also.  It's from Mastering HDR Photography by Michael Freeman.
"To clear up any confusion about dynamic range and bit depth, the number of bits determines the precision of the capture--how many steps the range of brightness can be recorded as.  In other words, a 14-bit sensor is more accurate than a 12-bit sensor.  Though it might, it does not necessarily capture a wider range, but more detail within the range.  The real limit to the range of a sensor is the amount of noise in the shadows."  
I guess my earlier quote from the other book says "potential dynamic range" not that bit depth = dynamic range, an oversight of mine to assume it did.

Although my mind isn't completely wrapped around the info you all possess, and are taking sides on, I feel there is much to learn from both sides.  Keeping the original raw files certainly makes the most sense as they are smaller and preserve the original data.  My question was provoked not as a study of dynamic range in tiff vs raw, but in recovery.  By deliberately pushing EV either + or - so that your image looks bad (the furthest PS or LR allows is -4 or +4), after saving as a tiff or raw file could you recover it to the original look.  My thought at first was maybe you could.   This all depends on how much DR can be preserved in these files and if the range is preserved equally on both sides to determine if this will work with both +4 and -4 effected images.

After looking at my test I realize the Exposure tool within PS is different than Exposure in Lightroom.  Though opening the +4EV DNG in ACR I can easily move the exposure slider back down and get my original image, if I were to open it in Photoshop without touching it in ACR and use the Exposure tool in Photoshop it appears the same way the Tiff looks when I try to recover using the Exposure tool in Photoshop.  So I guess my test is flawed.

There is a reason why I'm experimenting with this.  I create time lapses.  In situation such as sunsets it's very hard to photograph because you have to adjust your exposure every few minutes for the changing light conditions.  This makes terrible exposure jumps when you create a image sequence, unusable.  I've found using Lightroom you can "match total exposures" to smooth out the jumps.  But in the case of a sunset as it gets darker and you've compensated by increasing shutter speed, after you "match total" exposures LR will apply drastic -EV to compensate for the increased shutter speed.  I was hoping by saving as a 16bit Tiff or DNG that info would be preserved so that I could use After Effects to create a sequence and apply a gradual exposure increase throughout.  

What do you guys think?

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digitaldog
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« Reply #21 on: March 03, 2010, 05:23:41 PM »
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Quote from: Marshallarts
"To clear up any confusion about dynamic range and bit depth, the number of bits determines the precision of the capture--how many steps the range of brightness can be recorded as.  In other words, a 14-bit sensor is more accurate than a 12-bit sensor.  Though it might, it does not necessarily capture a wider range, but more detail within the range.  The real limit to the range of a sensor is the amount of noise in the shadows."

The old analogy that still holds up (well for those of us that agree with the above) is this: Dynamic range is akin to the distance in a staircase. Bit depth is the number of steps in the staircase. You can have a staircase that is 20 feet from bottom to top. One could have 20 steps, one could have 40 steps. The distance (dynamic range) is the same. More steps doesn’t alter the height of the staircase.
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Andrew Rodney
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vandevanterSH
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« Reply #22 on: March 03, 2010, 05:28:49 PM »
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And TIFF is normally locked into a gamma encoded color space while original raw captures are in linear gamma with the cameras' spectral response as color data.

Once you take that raw file and process it into a gamma encoded color space the distribution of tone is no longer linear so all the data that is clumped near the highlights has been redistributed. The will severely limit the amount of highlight recovery you can to to a processed TIFF file...
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Over my head but from a "users" perspective, am I better off exporting 16 bit TIFF or DNG from Phocus and then to import into LR or PS?

Steve
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bjanes
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« Reply #23 on: March 03, 2010, 05:47:51 PM »
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Quote from: Schewe
Here is the image I was referring to that proves that the brightest stop of a linear capture contains a lot of useful (and usable) data...perhaps a real image is more useful than theory?

This is the default image inside Camera Raw showing the histogram far, far to the right.

Here is the result of Camera Raw adjustments which ironically only used a -0.08 Exposure and Recovery of 45. The Brightness was at -113 and the Blacks pinned at 100 to draw the upper data down. In the Parametric Curves Shadows were also set to -100 while in the Point Curve editor the upper tonality was teased apart...

So, yes, I think it can be said the brightest stop of data in a raw capture has a ton of useful image data...no?
Yes, there are useful data in that brightest f/stop, but Ray stipulated that there should be no clipping in the image prior to its rendering into a 16 bit TIFF. Your image appears strongly clipped and violates Ray's stipulation and also my prior stipulation. It remains to be shown that with non clipped files RAW is superior to a 16 bit TIFF (or PS 15+1). There are editors other than Photoshop.  

Highlight recovery could not have been performed in a white balanced TIFF. Also, have you looked at the actual raw file to see how much clipping is really present?. You can't necessarily rely on the camera or ACR histogram to reflect the raw values.
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bjanes
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« Reply #24 on: March 03, 2010, 06:16:15 PM »
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Quote from: digitaldog
The old analogy that still holds up (well for those of us that agree with the above) is this: Dynamic range is akin to the distance in a staircase. Bit depth is the number of steps in the staircase. You can have a staircase that is 20 feet from bottom to top. One could have 20 steps, one could have 40 steps. The distance (dynamic range) is the same. More steps doesn’t alter the height of the staircase.
That is a good analogy that Bruce used to use, but it does not apply to linear files where the step size is very large in the shadows and small in the highlights as shown in Figure 2 of this reference and DR is limited by bit depth; gamma encoding improves the DR somewhat for a given bit depth. These limitations are shown in Table 2. For true HDR you need log or floating point encoding. I think that Bruce's analogy would apply with these encodings.

Also, please review my references in my prior post. There is not really much room for reasonable argument.

Norman Koren
Cambridge in Color



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Schewe
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« Reply #25 on: March 03, 2010, 08:47:15 PM »
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Quote from: vandevanterSH
Over my head but from a "users" perspective, am I better off exporting 16 bit TIFF or DNG from Phocus and then to import into LR or PS?


Unless you are doing image adjustments that require demosiacing (such as lens correction) you would be better off outputting a DNG and dealing with the raw processing in Lightroom if that is where you want to do your raw processing and also assuming that Phocus exports a raw DNG as apposed to a Linear DNG that has had the demosiacing done.

A "Linear DNG" is basically like a TIFF file in Pro Photo RGB color but with a linear gamma. DxO is an example of a raw processor that is capable our doing substantial lens based correction but needs to do the demosiacing so all it can output is a linear DNG.

So, does Phocus output a raw DNG or a linear DNG? (and do you need t do lens corrections?)
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scott morrish
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« Reply #26 on: March 04, 2010, 04:40:27 PM »
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As a p65 user who prefers LR to C1 in some areas, I have resorted to using C1 to export DNG's that i can then work with in LR.
In light of this thread, are C1 DNGs raw or linear? I had simply assumed they are raw... until i read this thread!

And... is there an established 'optimal' workflow for those of us with raw files that LR won't work with, but who'd still much rather process images in LR than C1?
And... will LR ever be able to deal with P65 files (please)?

Thanks for any help,
Scott
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Schewe
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« Reply #27 on: March 04, 2010, 04:48:10 PM »
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Quote from: scott morrish
In light of this thread, are C1 DNGs raw or linear? I had simply assumed they are raw... until i read this thread!

C1 writes out regular raw DNGs not linear. However if you want to use C1 for lens corrections (like on my Phase One 645 lenses) then you must actually process out as a TIFF.

In terms of workflow...when shooting to a card, I let C1 import and then to a DNG process output then import into LR. If I'm shooting tethered I do the same thing...

As for LR directly supporting P65+ files, yes...LR will be able to directly read P65+ files...don't know if it'll be in a 2.x update of a 3.0 version.
« Last Edit: March 04, 2010, 04:52:10 PM by Schewe » Logged
vandevanterSH
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« Reply #28 on: March 04, 2010, 05:19:44 PM »
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Quote from: Schewe
Unless you are doing image adjustments that require demosiacing (such as lens correction) you would be better off outputting a DNG and dealing with the raw processing in Lightroom if that is where you want to do your raw processing and also assuming that Phocus exports a raw DNG as apposed to a Linear DNG that has had the demosiacing done.

A "Linear DNG" is basically like a TIFF file in Pro Photo RGB color but with a linear gamma. DxO is an example of a raw processor that is capable our doing substantial lens based correction but needs to do the demosiacing so all it can output is a linear DNG.

So, does Phocus output a raw DNG or a linear DNG? (and do you need t do lens corrections?)


I found a year old thread on LL that addressed some of these issues w/o hard answers.  http://luminous-landscape.com/forum/index....showtopic=31079

 I will try the analogous C1>DNG> LR and see how that works.  Besides lens correction the big difference in card download > Phocus vs. card >LR are much more accurate color "out of the box" and a very big difference in shadow recovery and noise.  I am not certain how much of these differences are intrinsic to the software and how much are user correctable.

Steve
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scott morrish
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« Reply #29 on: March 05, 2010, 06:15:27 AM »
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Quote from: Schewe
As for LR directly supporting P65+ files, yes...LR will be able to directly read P65+ files...don't know if it'll be in a 2.x update of a 3.0 version.

Thank you Jeff.

Very exciting about LR and P65+ files.
Do you know if LR will be able to handle the 15mb Sensor+ files as well as the normal 'huge' files?

Scott
« Last Edit: March 09, 2010, 12:24:33 PM by scott morrish » Logged
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