AXIOM Alpha Color Modes Update
Submitted by Sebastian on Fri, 05/30/2014 - 22:09
The rather unfortunate wiring of the HDMI encoder chip on the Zedboard of AXIOM Alpha makes it impossible to use any full (4:4:4) color mode, because there are just not enough data input lines to transfer a complete pixel. The only modes we can use are those where partial data for two pixels is transmitted and the missing parts are interpolated by the encoder (ADV7511). The mode we started with was the rather strange RGB 2:4:2 mode where pairs of red/green and green/blue are sent and both red and blue are interpolated over two adjacent pixels by the encoder.
Certain sample footage that contains straight edges therefore shows red/blue borders on those edges because of the difference between the red and blue values. In order to compensate for this effect, we recently used the color transformation matrix of the HDMI output pipeline to transform the RGB values into YCbCr, which is also transmitted as partial information (Y/Cb and YCr this time) but provides luma information for every pixel. This enhances sharpness as the luma part is pixel accurate and somewhat reduces the color effects on the edges.
Notes:
- AXIOM Beta will not be limited to partial pixel data (chroma subsampling) on the HDMI output, so this specific problem only applies to the AXIOM Alpha hardware.
- This is unrelated to the spatial color differences caused by the Bayer pattern and aliasing effects in general.
- Bayer pattern color image sensors produce a similar but unrelated effect with very fine details as objects which project on small areas always result in the object only being visible to a single red, blue or green sensel but not to all of them.
and the AXIOM project is certified Open Hardware by
.
7 Comments
If I recall correctly the 3rd
If I recall correctly the 3rd note is how the Elphel Eyesis 4 Pi is able to refocus after shooting. The camera calibration is known for a fixed focus lens. Each different color, has a different wavelength thus allows to refocus on that specific wavelength or a mixture thereof. Reading this is worth your time: http://blog.elphel.com/2011/10/subpixel-registration-and-distrortion-mea...
please also consider using
please also consider using the sony imx 174 chip. A cmos global shutter high sensitivity chip and high frame rate chip if you want to investigate other complementary chip technologies. Apparently it does much better in low light than other cmos chips in global shutter mode.
No problem, all we need to
No problem, all we need to consider a sensor is a publicly available technical datasheet which describes the electrical interface and the sensor configuration in detail. So please provide a link to this datasheet for the sensor in question (I presume IMX174LLJ/IMX174LQJ is the one you mean). Thanks!
So what date will the Alpha
So what date will the Alpha camera be released?I really want to know so i can get it as soon as possible.
Because the AXIOM Alpha is
Because the AXIOM Alpha is difficult/expensive to replicate we announced the AXIOM Beta, a miniaturized, simpler to build and more feature rich version of the Alpha. Crowdfunding soon.
Can it be made without the
Can it be made without the Bayer filter for a true b&w camera?
Yes, quite easily. It just
Yes, quite easily. It just requires swapping the image sensor for the monochrome version.
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