disable color balancing on XO webcam

Gary C Martin garycmartin at googlemail.com
Mon Oct 25 11:34:58 EDT 2010

Hi Sebatian,

On 25 Oct 2010, at 15:28, sebarocker at gmail.com wrote:

> Hi, 
> Im working on a computer vision project in the XO and i would like to disable the color balancing on the XO webcam but i don't know how.
> In this link http://wiki.laptop.org/go/Hardware_specification says that it is posible :)

This reminded me of some distant email threads, here's a quick copy paste from my archive of them, in case any are of help.


--- copy & paste 1 ---

> From: Benjamin M. Schwartz <bmschwar at fas.harvard.edu>
> Subject: Re: [Sugar-devel] [ASLO] webcam images and control
> Date: 25 February 2010 16:46:29 GMT
> Aleksey Lim wrote:
>> On Thu, Feb 25, 2010 at 03:39:26PM +0100, Emmanuel Di Folco wrote:
>>> I would like to be able to :
>>> - control the gain or integration time of the camera (mode Photo, not  
>>> video) in order not to saturate (this is obviously feasible, since  
>>> the images taken during the day are not saturated !)
>>> - eventually restrict the size of the screen window that is  
>>> considered by the 'automatic gain adjustment algorithm' (where I  
>>> would insert the moon)
> The automatic gain adjustment is performed in hardware, not software.  In
> the standard mode, the CPU has no control over the camera's gain/exposure
> time.  It may be possible to put the camera into a "manual" mode, where
> the CPU can control gain and other parameters, but I do not know how to do
> this.
> The best person to ask is Jonathan Corbet, who wrote the camera's driver.
> However, the camera's interface has proven difficult to work with and
> poorly documented, so many advanced functions have not been implemented in
> the driver.  On the XO-1.5, even basic camera functionality is still not
> working correctly.
>>> - gather the raw images, not the JPG compressed ones.
> I did manage to do this on the XO-1.  You can try the instructions from:
> http://lists.laptop.org/pipermail/devel/2008-February/011029.html
> This code also controls the "integration time" by acquiring many images
> and averaging them.
> --Ben

--- copy & paste 2 ---

> From: Brian Jordan <brian at laptop.org>
> Subject: Re: Panorama activity
> Date: 12 October 2008 06:39:45 GMT+01:00
> On Sat, Oct 11, 2008 at 10:26 PM, Nirav Patel <olpc at spongezone.net> wrote:
>> My roomate and I wrote an auto-stitching Panorama Activity during the
>> Yahoo Hack Day at CMU yesterday (ended up winning the Hack for Good
>> award).  I'll be posting it in the wiki at some point today.  It needs
>> a whole lot of polishing, since it was written in 24 hours.
>> I ran into the same problem that Ben did with autowhitebalance and
>> autoexposure.  I looked through the ov7670 driver, and it seems
>> changing V4L2_CID_BRIGHTNESS should flip the auto exposure control
>> (AEC) bit in one of the registers.  I added support for changing
>> brightness to the camera module in Pygame, but either disabling AEC
>> doesn't work, or it just makes auto gain control and auto white
>> balance work even harder to change the image.  Other than that, the
>> stitching seems to work ok.  I'm going to pyramidize it at some point
>> to make it faster, and do something to improve the accuracy.  The
>> slowness of stitching doesn't effect the user experience much though,
>> because it only stitches after the user is done taking the pictures.
> So cool -- can't wait to try.
>> The Activity we wrote uses the Flickr API for an upload to Flickr
>> button.  I feel that this is the most important part.  There is
>> support for saving the stitched images as Journal entries, but it
>> would be wonderful if a kid anywhere in the world could see panoramas
>> taken by other kids elsewhere.  Flickr is far from ideal for this.
>> Beyond not really being designed for viewing panoramas, it is
>> currently set up to just upload every picture to my personal Flickr
>> account.  My API key, secret key, and an authentication token are
>> prerecorded in the activity, so anyone could potentially use those
>> values to edit existing photos and upload whatever to my Flickr
>> account:  http://flickr.com/photos/nrpatel/
> Awesome! :-D
> Maybe one could set up a one-way upload script for this on dev (or
> some appropriate
> community-developed-web-services-server-of-the-future)? This script,
> then, could handle the uploading via flickr API securely.
> Regards
> Brian
>> It seems Gigapan doesn't have an upload API.  gigapan.org works in
>> Browse on my os767 XO, but panning around an image is pretty slow.
>> Anyone have ideas on this?  A better way to Flickr, ideas for
>> designing a new site, getting Gigapan to add an upload API, etc?
>> The other issue we ran into is integrating OLPCGames with pyGTK stuff.
>> We used OLPCGames to take advantage of capturing the images as SDL
>> surfaces, but we also wanted pyGTK to pop up a Dialog box when the
>> user hits Save, asking for a Title, Tags, and a Description of the
>> panorama.  We hacked together something that does pop up the box and
>> saves correctly, but fails to ever destroy the box.  It then just sits
>> with the box open, preventing the user from using or exiting the
>> Activity.  Is it possible to use pyGTK beyond the toolbox while still
>> using OLPCGames?
>> Nirav
>> On Fri, Sep 5, 2008 at 6:41 PM, Jeff Keller <jeff.keller at gmail.com> wrote:
>>> Yeah -- I sent my loaner unit off to Burning Man, but I should get it
>>> back soon, and I'd be delighted to talk about stitchers.  Randy
>>> Sargent and I wrote our own for GigaPan last summer because nothing
>>> else was up to the task.  It relies on a model of the GigaPan device's
>>> behavior to do rough placement, but it can auto-stitch 1000+ images
>>> with < 10 pixels rms displacement error, and it should be open-sourced
>>> one of these days.  Of course, it uses much more storage, RAM, and CPU
>>> than an XO has, but nothing inappropriate to what it does, and there
>>> are some nice improvements in the works.  Oh, and my office is down
>>> the block from OLPC's.
>>> --Jeff
>>> On Fri, Sep 5, 2008 at 12:38 PM, Samuel Klein <sj at laptop.org> wrote:
>>>> Speaking of which, Jeff Keller has been trying to get OLPC folks to
>>>> learn more about using his gigapan group's cameras (and perhaps to
>>>> borrow one to bring them into a country for weeks) for a while.  Jeff,
>>>> Ben Schwartz and Nirav are really interested in large-scale image
>>>> splicing...
>>>> SJ
>>>> ---
>>>> 617 529 4266
>>>> On Fri, Sep 5, 2008 at 2:08 AM, Brian Jordan <brian at laptop.org> wrote:
>>>>> *bump*
>>>>> http://wiki.laptop.org/go/Panorama_camera_activity
>>>>> (code? Nirav is interested in doing something similar!)
>>>>> Brian
>>>>>> On Wed, Jun 20, 2007 at 11:56 PM, Benjamin M. Schwartz <bmschwar at fas.harvard.edu> wrote:
>>>>>> Hash: SHA1
>>>>>> The XO happens to be perfect for shooting stitched panoramic photographs, due to
>>>>>> the swivel design.  I tested it out in the OLPCHQ lobby. Then, I wrote a simple
>>>>>> panorama stitcher in 50 lines of Python.  It runs in 3.4 seconds on my Core Duo,
>>>>>> producing this output:
>>>>>> http://people.fas.harvard.edu/~bmschwar/lobby_ugly.jpg
>>>>>> The results aren't too bad.  I also tried stitching this scene with Hugin, the
>>>>>> most powerful panorama stitcher I know of.  Hugin required significant user
>>>>>> intervention and half an hour of computing time, producing this output:
>>>>>> http://people.fas.harvard.edu/~bmschwar/lobby_pretty.jpg
>>>>>> This scene is unusually difficult because of the huge indoor-outdoor contrast.
>>>>>> Given this positive result, I would like to work on a panorama-making activity,
>>>>>> possibly inside Capture.  I know that at age 10, I loved making panoramas out of
>>>>>> photographs.  Panoramas provide an immersive way for children to communicate
>>>>>> their environments to each other and to the world.
>>>>>> - --Ben Schwartz
>>>>>> -----BEGIN PGP SIGNATURE-----
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>>>>>> =v5GB
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