Median filtering is computationally intensive at large extents, and Matlab is poor at parallelizing this operation. Here’s a graph of some timings for one-dimensional filtering of a 6000×56000 pixel image using both median filtering and averaging with a block filter of the same size as the median filter’s extent: I did a series of analyses… [Read More]
Downsampling and averaging
In yesterday’s post, I downsampled images successively, a factor of two at each step, in an attempt to get averaging at the same time. I was working with the images today, and it didn’t look like I was getting the desired effect. Then it hit me. I was doing exactly the wrong thing. Downsamping by… [Read More]
Mitigating subject motion in slit scan images
As many of you know, I’ve been doing slit scans of plants, and I’ve been struggling with image artifacts due to subject motion. In the past few days I’ve been working on a Matlab program to deal with the artifacts and at the same time assemble several images into a complete, visually seamless composite. In… [Read More]
Traveling with Sony alpha 7’s
I returned on Sunday from a 9-day trip to the Canadian Rockies, staying outside of the town of Banff. It wasn’t specifically a photographic trip. It was mainly a family holiday. But, of course, I planned to make photographs. What kind of photographs? I thought a little landscape work even though the times of best… [Read More]
Nikon D810 high-ISO noise reduction
Yesterday’s experiments with the D810 dark-field noise, which showed that Nikon employs some low-pass filtering when long exposure noise reduction is turned on, made me wonder if there was any similar filtering at high ISO settings, a la the Sony a7S. I looked at one of the green channels of exposures made at ISO 64… [Read More]
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