[Elphel-support] RGB artifacts

[Andrey Filippov]

Nathan,

These are "warm" pixels (ones that have increased dark current, their value
depends on the exposure time) - you may find such pixels on our panorama
images also. Most of the Aptina sensors we use have some number of warm and
even hot pixels (those that generate maximal output value regardless of the
exposure time) and the manufacturer does not offer different grades of the
sensors. Many cameras have built-in code to wipe such pixels out (replacing
their values by the average value from the neighbors) but we did not yet
implement such code in these cameras because most of the applications
involved some post-processing anyway and our main focus is to preserve the
actual sensor data in a reasonably "raw" form. So currently the only way to
eliminate such pixels is to do it with the post-processing.

Additionally you will see less of the "warm" pixels if the exposure time
goes down from the 1/30 sec you have on those samples, only "hot" pixels
will remain.

To measure the value of such pixels it is better to capture JP46 image (or
just monochrome), so each pixel will have the original value, not the one
mixed with the neighbors.

You may find discussion on the warm pixels in the earlier posting:

http://www.mail-archive.com/support-list@support.elphel.com/msg00113.html

Andrey


On Thu, May 19, 2011 at 7:20 PM, Nathan Clark <throwstone at gmail.com> wrote:

> Hi Andrey,
>
> Here is a grab for you at full frame:
>
> http://dl.dropbox.com/u/792881/Apertus%20Forum/Misc/RGB_Artifacts_2592x1936.jpg
>
> and one at 1024x768
>
> http://dl.dropbox.com/u/792881/Apertus%20Forum/Misc/RGB_Artifacts_1024x768.jpeg
>
> I have shot this with the iris closed down. As you can see, dotted all over
> the place are little R/G/B hot pixels.
>
> I certainly hope we can fix this easily enough!
>
> Kind regards,
>
> Nathan.
>
> On Fri, May 20, 2011 at 7:47 AM, Andrey Filippov <
> support-list at support.elphel.com> wrote:
>
>> Nathan,
>>
>> I'm sorry you have such artifacts. Can you please send the sample images
>> from the camera(s) with these artifacts? We test all the cameras before
>> shipping and it is very unlikely for the two cameras to have same hardware
>> problems - it might be something else.
>>
>>
>> Andrey
>>
>>
>> On Thu, May 19, 2011 at 10:38 AM, Nathan Clark <throwstone at gmail.com>wrote:
>>
>>> Hi there,
>>>
>>> My partner and I just received 2 elphel 353 cameras.
>>> I am noticing alarming artifacts appearing from both of them
>>> (one camera more so than the other)
>>>
>>> It seems that scattered across the sensor- there are bright pixels- some
>>> Red, some Green, and some Blue. These artifacts are constant and unmoving-
>>> and become more obvious at lower resolutions. Is this a hardware fault for
>>> which I should be seeking replacement?
>>>
>>> Before going that far, I thought I would consult with this list to see if
>>> anyone has any ideas. If this is an uncommon problem, i can take grabs off
>>> the sensor- or if this is a common problem- then you know what I'm talking
>>> about.
>>>
>>> Kind regards,
>>> Nathan
>>>
>>>
>>> _______________________________________________
>>> Support-list mailing list
>>> Support-list at support.elphel.com
>>>
>>> http://support.elphel.com/mailman/listinfo/support-list_support.elphel.com
>>>
>>
>>
>>
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>>
>
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