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| 04:37 | Bertl | off to bed now ... have a good one everyone!
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| 13:30 | Bertl | morning folks!
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| 19:21 | se6astian | I am back!
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| 19:21 | se6astian | good evening
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| 19:21 | Bertl | \o/ wb
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| 19:22 | troy_s | Bertl: Can you concoct a method to determine the strictly linear region of the sensors?
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| 19:23 | troy_s | Bertl: (for any given set of variables such as voltage etc.)
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| 19:24 | se6astian | thanks, ordering oshpark now as requested
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| 19:27 | Bertl | troy_s: recently a colleague suggested to use an integrating sphere for such tests
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| 19:29 | troy_s | Bertl: Explain?
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| 19:29 | troy_s | I ask because it is important for the resultant generation of the conversion LUTs.
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| 19:30 | troy_s | Using only the linear region is going to yield entirely unacceptable results for both post production and photographers as the highlight roll off won't be terribly accurate.
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| 19:31 | troy_s | So my desire is to craft a process that generates accurate 3D LUTs across the entire sensor range, for each of the ISO gain settings etc. Similar to what Arri does for the Alexa LUTs.
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| 19:31 | Bertl | se6astian: thanks!
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| 19:31 | Bertl | I think the process can be fairly automated
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| 19:32 | troy_s | Under controlled lighting
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| 19:33 | troy_s | My gut says a very good 3D LUT can be generated off of several test charts that pin each of the sensitivity regions
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| 19:33 | troy_s | Not sure how to actually generate the data from the chart positions (simplistically say, a chart at linear region, a chart near floor, and a chart near head.)
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| 19:34 | troy_s | Probably plausible doing it in subsequent shots using ND or netting lights down, doesn't matter tremendously here.
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| 19:34 | troy_s | Merging the data is where it gets murky here. How to interpolate from one chart data set to the next.
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| 19:35 | troy_s | Basically, in post (and why highlight recovery is a bad idea) one wants accurate RGB representations across the entire range. Matrix / single linear region chart reads aren't going to deliver this.
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| 19:37 | Bertl | sounds like you would like an Early Beta ASAP :)
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| 19:37 | troy_s | Well I would prefer it if a big brainer can help me come up with the process first.
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| 19:38 | troy_s | Bertl: Any ideas on how to merge a series of charts?
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| 19:44 | Bertl | well, the chart is supposed to give correct results (after processing) under certain circumstances (within the range)
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| 19:45 | Bertl | it will result in a volume which maps (R,G,B) tuples to (X,Y,Z)
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| 19:45 | Bertl | (in the most generic form)
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| 19:46 | Bertl | so, given that all charts are within the range (no clipping) but differently illuminated you should get the same mapping, no?
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| 19:47 | Bertl | so I would say, the resulting transformations can be combined or averaged
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| 19:50 | troy_s | Bertl: Except the sensor is nonlinear in regions
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| 19:50 | troy_s | In particular, that upper edge of importance.
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| 19:51 | troy_s | So what I am hoping for is a 3D LUT that accurately models both that curve and the curve near the toe such that we get accurate transforms.
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| 19:51 | Bertl | shouldn't matter if the transformation is correct
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| 19:51 | Bertl | don't forget, the non-linear range is only problematic for matrices
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| 19:51 | troy_s | Exactly
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| 19:51 | Bertl | (which cannot compensate for that easily)
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| 19:52 | troy_s | The issue is that we can only sample the chart at a given intensity range.
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| 19:52 | troy_s | So if we have a chart at say, the range the display referred paper can represent, then another chart near the edge of the sensor head
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| 19:52 | troy_s | We have two charts worth of data to merge into a 3D LUT.
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| 19:53 | troy_s | The latter representing that critical highlights range.
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| 19:53 | Bertl | yes, and both will give an overlaping volume
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| 19:53 | troy_s | The problem is feathering between the two 3D LUTs.
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| 19:53 | troy_s | Exactly.
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| 19:54 | Bertl | as I said, if the process (chart to transformation) is not flawed, the overlaping regions should be (almost) identical
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| 19:54 | troy_s | Somehow interpolating those, because they obviously won't be a precise match such that we could simply concatenate after two truncs.
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| 19:55 | troy_s | Hrm... Maybe a simple truncation would suffice. Was hoping for something a tad more elegant.
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| 19:55 | Bertl | average?
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| 19:56 | troy_s | Linear average across the 3D LUT values for a curved range where the seams are?
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| 19:56 | Bertl | if they differ significantly, the mapping process is flawed
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| 19:56 | troy_s | Well they will be close.
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| 19:57 | Bertl | you can also fade one into the other
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| 19:57 | troy_s | That is exactly the idea. Feather the seams.
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| 19:57 | troy_s | More dense (say a series of bracketed shots) would yield more accurate results.
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| 21:11 | se6astian | time for bed
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| 21:11 | se6astian | good night
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