Brian Sweeney
Woodbridge, VA
Forum Replies Created
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Re: Sony A7R3 shoot compressed or uncompressed?Reply #1 on: September 15, 2019 at 6:31 pm
To see this one would implement the compression algorithm and run it on an uncompressed image and store the difference frame.
The way you calculate the difference frame is important.
https://blog.kasson.com/the-last-word/a-tough-test-of-sony-raw-compression/
What I mean by this: Implement the compression algorithm in software to post-process an uncompressed raw image. Compress the image, decompress it and then subtract from the original uncompressed image. That will show what is being lost by the compression algorithm.
For doing a running sum difference frame on a Mosaic Sensor: do a running difference of elements of the same color on the same row. Store the differences as 8-bit signed values from -127 through +126, reserve 127 as an escape value to store the actual value for when the difference exceeds -127:126. If the encoded difference frame exceeds the original image size, switch to storing an uncompressed frame. Computationally expedient, best to store the original image if the running difference takes too much space. The point response of the sensor+lens is important, tends to work best on oversampled data. Worked 30 years ago.
My Micro-Nikkor AFD 200/4 is one of the sharpest lenses that I own. Online reports state that it is well matched to a 16MPixel sensor. I wonder how many Sony A7RIII images are taken using lenses that outperform the sensor.
Re: Sony A7R3 shoot compressed or uncompressed?Reply #3 on: September 15, 2019 at 1:03 pmhttps://www.ingentaconnect.com/contentone/ist/ei/2016/00002016/00000002/art00020?crawler=true
A paper on how ARW v2 (Alpha Raw) works, and a program available to correct artifacts. Worth reading just for the reference to Blondie. But anyone with the album would realize the parallel lines were B&W.
Re: Sony A7R3 shoot compressed or uncompressed?Reply #4 on: September 15, 2019 at 9:37 amSome web-surfing: One reference that the compressed mode raw of the Sony A7RIII uses 12-bit pixels when shooting burst mode and long exposures. There was a link to a Sony statement about the switch to 12-bit, but Sony seems to have moved or removed it- link was dead. The first step of the Sony compression algorithm on the older series cameras (at least what has been documented through users online) is to reduce the 14-bit raw value to 12-bits. If you require pulling out details from shadows, it is best to have the full 14-bits available. The other effect this has is to lose fine detail in the image: 4 intensity values are binned into one value. This is like making a contour map of the (intensity/ 4). Noise in the image can move pixels near the edge of a contour line to the next bin. To see this one would implement the compression algorithm and run it on an uncompressed image and store the difference frame.
If you like the results with compressed mode- use it. If you cannot see a difference, it works for you. If you do a lot of post-processing, uncompressed raw provides more information to work with. Memory cards are huge these days. You can always shoot uncompressed, and “ZIP” the raw files on your computer to store them when not in use or for archiving. Algorithms such as ZIP will compress an uncompressed raw image without decimating the data.
