December 21, 2010

“Zoom in. Now… enhance.” – results

by Andrey Filippov

UPDATE: The latest version of the page for comparing the results.

This is a quick update to the Zoom in. Now… enhance. – a practical implementation of the aberration measurement and correction in a digital camera post published last month. It had many illustrations of the image post-processing steps, but lacked the most important the real-life examples of the processed images. At that time we just did not have such images, we also had to find out a way to acquire calibration images at the distance that can be considered “infinity” for the lenses – the first images used a shorter distance of just 2.25m between the camera and the target, the target size was limited by the size of our office wall. Since that we improved software combining of the partial calibration images, software was converted to multi-threaded to increase performance (using all the 8 threads in the 4-core Intel i7 CPU resulted in approximately 5.5 times faster processing) and we were able to calibrate the two actual Elphel Eyesis cameras (only 8 lenses around, top fisheye is not done yet). It was possible to apply recent calibration data (here is a set of calibration files for one of the 8 channels) to the images we acquired before the software was finished. (more…)

November 18, 2010

“Zoom in. Now… enhance.” – a practical implementation of the aberration measurement and correction in a digital camera

by Andrey Filippov

Deconvolved vs. de-mosaiced original

This post describes the implementation of the optical aberration measurement and correction developed for Elphel Eyesis cameras, the same methods and the code (available under GNU GPLv3) can be applied to many other camera systems. With 1/2.5″ 5 megapixel sensor we achieved average sharpness improvement over the image area around 40% compared to the raw images, effectively doubling the resolved pixel count. The applied correction varied significantly with the location on the image plane, orientation and color channel, making simple uniform isotropic sharpening (i.e. with “unsharp mask” or similar filtering) useless in our case. The aberrations correction is based on well-known measurement and inversion of the system point-spread function (PSF), additionally we describe used frequency domain de-mosaic filtering (“spectral scissors”) compatible with the inverted PSF convolution.


June 24, 2010

Elphel Eyesis camera optics and lens focus adjustment

by Andrey Filippov

Designing for low parallax

When we started working on Eyesis project our first goal was to make the panoramic head as compact as possible to reduce parallax between sensors. That not only reduces the stitching artifacts but also decreases the minimal distance to object without dead zones between the individual camera.

The first practical step was to reduce the PCB area around the sensors, especially in one direction, so multiple camera boards can be placed closer to each other, For that purpose we preserved the basic design of the proven 10338 sensor board, just changed the layout to make it more compact. The board 10338D is just 15mm wide – more than twice less than the older design.

Next step was to run mechanical CAD program and try to place the boards and lenses. Most of the Elphel cameras were designed for the C/CS-mount lenses, but when I tried to place them I immediately found out that when using 10 or 8 cameras around even the C-mount thread (CS is the same size but even closer) will be the limiting factor, not the sensor PCB that we already made smaller.

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