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08-06-2016, 02:26 AM   #1591
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QuoteOriginally posted by Logics Quote
I had a misunderstanding about what you meant here but let us not mix things up. Pentax PixelShift takes you from a 14-bit RAW to a 42-bit RAW. PS was not designed for dynamic range increase, but for detail and colour accuracy increase. With 42-bits of data at each pixel, that is a great deal of dynamic range.
No this isn't 42EV of luminance information (what dynamic range is basically about) whatever the light frequency used (red, green or blue). This is at best 4X more dynamic range. So a best 4X would be 2EV if we were using photosites without color filters. Here it is less because colors frequencies are filtered. If we suppose that at photosite level the dynamic rnage is matching the number of bits of the file format, they we get a theoretical max of 16EV of dynamic range. Not 42.

If you take different exposures, you get much more information of that dynamic range because you record different part of the signal. But taking 5 pictures separated by 2EV each, you actually get 8EV of dynamic range. Pixel shift use the same strategy but for light frequency, not dynamic range. You can't have it all. Would you want both, then you'd get 4x5 = 20 image with pixel shift and different exposures.


Last edited by Nicolas06; 08-06-2016 at 11:34 PM.
08-08-2016, 02:28 AM - 1 Like   #1592
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QuoteOriginally posted by Nicolas06 Quote
No this isn't 42EV of luminance information
QuoteOriginally posted by Nicolas06 Quote
You can't store this information in a single raw/jpeg but a standard exist for 32 bit per pixel HDR files instead of 8bit jpeg or 12,14 or 16 bit raws.
I never said that nor suggested that PS stored 42EV of luminance. I specifically said that it was 42-bits per pixel or 14-bit per (R,G,B) per pixel. I also stated that a 32-bit per pixel file is still 8-bits per (R,G,B,A) per pixel and a 48-bit per pixel file is 12-bits per (R,G,B,A) per pixel. Exposure stacking by taking several exposures, e.g., one at -2EV, one at 0EV and one at +2EV then stacking them, still gives you only one colour per pixel, the actual luminance (and eventual colour) is still approximated at each pixel, and you still end up with three files out of camera. Stacking five gives you five files out of camera so the workflow has 3-5 times more data which still has approximated luminance and colour. PS gives one file out of camera with accurate colour and luminance data at 4x file size but simplified workflow.

As for OpenEXR, the HDR file format developed and used by ILM (and most others) boasts,
QuoteOriginally posted by OpenEXR:
“OpenEXR's features include: Higher dynamic range and color precision than existing 8- and 10-bit image file formats….”
Note that it did not mention 12-bit image file formats (which it arguably equals) nor 14-bit image formats (which beat it). That being said, it continues to say that it also supports a 16-bit float, a 32-bit integer, and a 32-bit float. But normal format is a 16-bit float because,
QuoteOriginally posted by OpenEXR:
32-bit floating-point TIFF is often overkill for visual effects work. 32-bit FP TIFF provides more than sufficient precision and dynamic range for VFX images, but it comes at the cost of storage, both on disk and in memory.
This is how it is described:
QuoteOriginally posted by OpenEXR:
ILM decided to develop a new HDR file format with 16-bit floating-point color component values. Since the IEEE-754 floating-point specification does not define a 16-bit format, ILM created the "half" format. Half values have 1 sign bit, 5 exponent bits, and 10 mantissa bits. For linear images, this format provides 1024 (2^10) values per color component per f-stop, and 30 f-stops (2^5 - 2), with an additional 10 f-stops with reduced precision at the low end (denormals).
In other words, it sacrifices colour data precision for increased luminance detail in the shadows. That is fine, considering the range for a reflected projected image and the way the human eye works. We see more luminance detail in low light but far less colour accuracy while we see great colour in bright light but less luminance detail. ILM and other movie studios really need the luminance detail for PP work and small file sizes are important when you have hours of footage at 24 individual images per second. Pentax's 42-bit integer PS files are larger with less luminance but more accurate colour in shadows (and are not shot at more than 4.3 individual images per second). This is great for when you want to pull out shadow details but keep its colour accuracy.

So using EXR at 32-bit integer, we get (signed) 10-bit per (R,G,B)+T per pixel (the pixel is either visible or invisible) or (unsigned) 8-bit per (R,G,B,A) per pixel (the pixel has 256 levels of transparency from invisible to opaque). Still not better than 42-bit unsigned (R,G,B) or 48-bit unsigned (R,G,B,A). Otherwise, we increase luminance drastically (dynamic Range) by sacrificing shadow colour significantly for 16-bit float. Or, we can choose to not sacrifice colour by going to 32-bit floating point. not to mention, more processing power needed for floating point colour components.

tl;dr →
Bracketing and storing in a HDR format over using one large 42-bit PS PEF/DNG either creates
① large sets of files (original bracketed shots plus post-processed composited HDR int file) with less dynamic range, complicating your workflow or
② a large set of files (original bracketed shots) plus one final image (post-processed composited HDR fp file) with colour detail lacking in the shadows but immense luminance detail (dynamic range), requiring intense processing power, complicating your workflow.

Last edited by Logics; 08-08-2016 at 02:36 AM.
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