[Elphel-support] Noise in Photo Finish/Line Scan mode

[Andrey Filippov]

Hello Linden,

Nice to hear you are making a progress with such systems. As you know we
did not use that mode much and there can be some unnoticed bugs in the code
(in stis case it is probably in the FPGA code). It seems to me that it is
related to the use of the neighbor pixels when doing the color conversion
(compressor has to look around and while compressing 16x16 macroblocks it
reads (from the video memory) overlapping 20x20 pixel blocks (actually
using just 18x18 ones), so in regular (not line-scan) mode camera reads
(w+4)x(h+4) frames from the sensor. The linescan mode is a special one and
I implemented some measures to get those missing pixels for the end of
frame, but obviously something is not working properly (I probably broke
the code at some point implementing other changes and did not re-test the
linescan mode) .

It may be not so easy to fix and I am not 100% sure that it is actually the
case,  but you may try a quick test (that can also be a fix). Try saving
images in JP4 (or JP46) format - we use it when we need higher quality
images as it bypasses (simple) color conversion (de-mosaic) in the camera
and saves raw Bayer pattern images. Here you can find some explanation -
http://community.elphel.com/jp4/jp4demo.php.

There are now multiple ways to process the JP4 images, I use plugin for
the  ImageJ:
http://elphel.git.sourceforge.net/git/gitweb.cgi?p=elphel/ImageJ-Elphel;a=blob;f=JP46_Reader_camera.java

Plugin opens the images and you can save them as 32-bit TIFFs

As the JP4 images do not involve any color conversion in the camera, the
extra pixels are not needed. And de-mosaic processing should probably be
performed on the stitched image, otherwise there still can be some
discontinuity on the border.

Andrey

On Wed, Jan 18, 2012 at 5:31 PM, Linden Mills-Connery <lmillsc at gmail.com>wrote:

> Hello Elphel community,
>
> I have been using the NC353 very successfully as a photo finish camera for
> a variety of sports and we have been having great success. At this point we
> are working on refining the system and one of the issues that has been
> niggling at us is the noise that get introduced at the bottom of a image
> when in photo finish mode. A few numbers to make sure we are on the same
> page:
> -Currently Installed Firmware Version: Elphel (R) Model 353 Camera release
> 8.0.9.2
> -Camera Serial Number: 00:0E:64:08:19:96
> -FPGA Release Number: 3534025
> -PF_HEIGHT=2
>
> So what I mean by noise is best represented by the following two images.
> The first is a full frame as recorded by the camera with VIRT_HEIGHT=256:
> http://zone4.ca/download/rapidcam/PF_Noise_Full_Image.jpg
> Looking at the bottom 16 pixels of the image, it is clear that something
> is not right. The bottom 8 pixels are the worst but the next 8 above that
> are a bit strange as well.
> I have done a zoom in on the bottom 32 pixels of this image as well:
> http://zone4.ca/download/rapidcam/PF_Noise_Zoom.png
>
> So when we put to successive frames together, we get the line near the
> middle left of this image:
> http://zone4.ca/download/rapidcam/PF_Noise_Line.jpg
> Note: this image has been rotated 90 degrees from what the camera
> originally recorded and has had two frames stitched together.
>
> I have tried various VIRT_HEIGHT values but had no success. Can you
> provide more insight on this problem?
>
> Thanks,
>
> Linden
>
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>
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