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Author Topic: DPRSplit: boost Canon's Dynamic Range by +1EV (Dual Pixel)  (Read 1152 times)

Guillermo Luijk

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DPRSplit: boost Canon's Dynamic Range by +1EV (Dual Pixel)
« on: February 11, 2018, 05:16:00 PM »

The guys from RAWDigger/FastRawViewer (Illiah if you are around here, I have a couple of suggestions below) have made a nice software to extract two RAW files from a Dual Pixel Canon (Canon 5D IV at the moment?) RAW file, allowing one extra stop of DR (this matches on a Canon 5D IV the Nikon D850 and Sony A7R III DR). The explanation of how it works here:

https://www.fastrawviewer.com/DPRSplit

I downloaded a Canon 5D IV Dual Pixel RAW file with a partially saturated sky. With DPRSplit I extracted the embedded two RAW files in DNG format; it works flawlessly. I developed equally both RAW files correcting exposure by 1EV to match them, and compare.

Quite notorious parallax. Actually I don't know how Dual Pixel works and how can it produce increasing parallax away from the focus plane, but 0 parallax over the focus plane:




Regarding noise and sharpness, the -1EV RAW file is noisier (about 1 stop noisier in the shadows) and sharper. I gues the increase of sharpness is due to the half pixel sampling which increases horizontal resolution, but also makes the capture more prone to aliasing. Sharpness freaks, I wonder if this sharpness increase could be a reason to use Dual Pixel by itself...




Let's go to the Dynamic range story: since the normal shot has the G channel saturated in the RAW file, but the -1EV RAW file has it intact as can be seen in the RAW histograms:

RAW 1: G clipped


RAW 2: all three channels intact


A standar RAW development (without colour inpaint algorithms) produces a monochrome sky, while the -1EV RAW file has the right colours throughout the entire sky:




An optimum fusion would take the sky from the -1EV RAW file and the rest from the normal RAW. It's important to minimise progressive blending since the parallax effect would ruin sharpness in the overlapping areas. I have calculated the pixel to pixel relative exposure in both RAW files, and the expected gaussian bell splits in two. I cannot interpret this now, but the relative exposure falls well close to 1EV as expected:



An optimal fusion (obtained with Zero Noise) suggests this fusion map:



Black areas are taken from the regular RAW file and white from the -1EV. Standard HDR blending software could produce issues if a hard blend is not performed. I would suggest simply to develop both RAW files separately, match exposure, and use a hard layer mask to "recover" the clipped highlights.


Two suggestions for the DPRSplit team:
  • Its Windows version doesn't allow window resizing and you need at least Full HD vertical resolution to fit the app on the screen. I had to install it on a second Full HD laptop.
  • Not sure if this is DPRSplit responsibility, but developing the DNG files with DCRAW, it uses a saturation point value of 12400. A closer inspection of the RAW file I downloaded reveals a more precise saturation point of 14335; log2(12400/14335)=-0,21EV. This means using the DNG sat. point can yield to unnecesarily clip up to 0,2EV in the highlights. In a context where we are trying to bring 1EV back to life, this is not desired.

Regards!
« Last Edit: February 11, 2018, 06:56:21 PM by Guillermo Luijk »
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DP

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Re: DPRSplit: boost Canon's Dynamic Range by +1EV (Dual Pixel)
« Reply #1 on: February 11, 2018, 05:41:27 PM »

they actually were going to announce it themselves ("в англоязычных ресурсах анонс сделаем сами"), but ... in any case the English is here = https://www.fastrawviewer.com/DPRSplit ( manual = http://updates.fastrawviewer.com/data/DPRSplit/DPRSplit-Manual-ENG.pdf )

more about Canon "dual pixel sensel" raw files :

https://www.rawdigger.com/howtouse/Canon-dual-pixel-technology

https://www.rawdigger.com/howtouse/canon-dual-pixel-mode-highlights-are-there
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Guillermo Luijk

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Re: DPRSplit: boost Canon's Dynamic Range by +1EV (Dual Pixel)
« Reply #2 on: February 11, 2018, 05:58:56 PM »

I know, I already posted the link to their site.

Iliah

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Re: DPRSplit: boost Canon's Dynamic Range by +1EV (Dual Pixel)
« Reply #3 on: February 12, 2018, 09:47:12 AM »

Dear Guillermo,

Thank you. I sent you a PM with the link to a new beta and some comments on what we've changed.
« Last Edit: February 12, 2018, 10:13:59 AM by Iliah »
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Iliah

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An update
« Reply #4 on: February 13, 2018, 11:12:24 AM »

This is version 0.8.2.12:

http://updates.fastrawviewer.com/data/DPRSplit/DPRSplit-0.8.2.12-x64-Setup.exe

http://updates.fastrawviewer.com/data/DPRSplit/DPRSplit-0.8.2.12.dmg

http://updates.fastrawviewer.com/data/DPRSplit/DPRSplit-Manual-ENG.pdf

Changes (they are reflected in the Manual, of course, too):

- font size on the first run (and margins for Windows) are set based on the screen size. If the base font size setting is changed to smaller, the application window is also changed to smaller, accordingly. Works OK with 1200 by 800 pixels screens. The control is in Preferences.

To facilitate the use of HDR applications:
- Adjust EXIF shutter speed by -1EV for second frame (for HDR merge) – simulates reduction of exposure by 1 stop by setting the shutter speed in the EXIF of the auxiliary frame 1 stop faster. This may be useful (and even necessary) while merging first and second frame in certain HDR stacking applications that analyze frames for exposure parameters.

For the first beta, we were careful not to confuse the raw converters that do not process the extreme highlights correctly. Now we offer a finer control in Preferences:

- Data Maximum: controls the content of the DNG White Level tag:

o Normal White –«white» will be set to the Normal White value found in makernotes of CR2 file.

o Specular White (default) – «white» will be set to the SPecular White value found in makernotes of CR2 file.

o Data Max (or specular) – «white» will be set to the actual maximum found in raw data of the CR2 file or to Specular White, if Specular White is higher.

o Data format max – 16383 (minus the black level if the processing mode is set to subtracting black). This option may result in color artifacts in the highlights (such as pink clouds) if the raw converter incorrectly clips the highlights after applying white balance.
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kirkt

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Re: An update
« Reply #5 on: February 13, 2018, 01:07:21 PM »

...

To facilitate the use of HDR applications:
- Adjust EXIF shutter speed by -1EV for second frame (for HDR merge) – simulates reduction of exposure by 1 stop by setting the shutter speed in the EXIF of the auxiliary frame 1 stop faster. This may be useful (and even necessary) while merging first and second frame in certain HDR stacking applications that analyze frames for exposure parameters.



Thank you for this time-saver!

kirk
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Iliah

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Re: An update
« Reply #6 on: February 13, 2018, 02:26:03 PM »

Thank you for this time-saver!

kirk

Well, that was your idea to begin with ;)
Thank you!
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