Brian Kimball
CA
Forum Replies Created
-
-
Re: Exposure Technique for Mirrorless using ZebrasReply #2 on: December 6, 2020 at 2:00 pm
This is really interesting. It’s commonly believed that mirrorless live histograms/blinkies/zebras are based on the data from the camera’s highly downsampled and processed EVF video feed. This zebra trick implies, at least on Sony cameras, that these live zebra warnings are based on data from earlier in the EVF image processing pipeline, which is potentially huge news for raw shooters desiring realtime exposure warnings.Sadly I don’t have a Sony camera to test this. It would be really informative if someone shot a static scene with a bright highlight with progressively increasing zebra warning levels, and compared those zebra warnings to the actual RawDigger histograms. The impact of different picture profiles and white balances on these zebra warnings set beyond 100% would be especially interesting.Edit: My comments above made the naive assumption that 100% = clipping in the processed video feed and that any value above 100% must indicate the zebras are based on unprocessed data.
After some googling I’ve found that the zebra percentages are likely in IRE units where 100% merely represents a maximum “safe” white value for a TV broadcast. Apparently it is common in video capture to go above 100% and that is only loosely correlated with clipping.
Re: The Optimum Digital ExpsoureReply #3 on: November 21, 2020 at 11:17 pmPhysicist Emil Martinec’s 2008 paper Noise, Dynamic Range, and Bit Depth in Digital SLRs remains the authoritative source on why ETTR actually works and why it’s not because there’s more bits available to store the brightest highlights vs the midtones or shadows.
Here’s an excerpt from page 3, but it’s definitely worth reading it from the beginning:
A common maxim in digital photography is that image quality is maximized by “exposing to the right” (ETTR) — that is, raising the exposure as much as possible without clipping highlights. It is often stated that in doing so, one makes the best use of the “number of available levels” in the raw data. This explication for instance can be found in a much-quoted tutorial on Luminous-Landscape.com. The thinking is that, because raw is a linear capture medium, each higher stop in exposure accesses the next higher bit in the digital data, and twice as many raw levels are used in encoding the raw capture. For instance, in a 12-bit file, the highest stop of exposure has 2048 levels, the next highest stop 1024 levels, the one below that 512 levels, and so on. Naively it would seem obvious that the highest quality image data would arise from concentrating the image histogram in the higher exposure zones, where the abundance of levels allows finer tonal transitions.
However, the issue is not the number of raw levels in any given segment of the raw data (as measured e.g. in stops down from raw saturation point). Rather, the point is that by exposing to the right, one achieves a higher signal to noise ratio in the raw data. The number of available raw levels has little to do with the proper reason to expose right, since as we have seen the noise rises with signal and in fact the many raw levels available in higher exposure zones are largely wasted in digitizing photon shot noise […]”
Regarding this Optimum Digital Exposure article… it seems like a smoothed over and aggressively marketed version of countless blogs on practical ETTR that have come before. Sorry, these concepts and techniques are not new. For example:
https://www.fastrawviewer.com/blog/spot-meter-exposure
https://www.fastrawviewer.com/blog/how-to-use-the-full-dynamic-range-of-your-camera
https://www.fastrawviewer.com/blog/exposure-bracketing
https://www.fastrawviewer.com/raw-histogram-for-culling
