Hi Kurt,

thank you for your answers. This helps a lot!

Regards,
Sabrina

Am 08.02.2011 15:27, schrieb Kurt Konolige:
> Sabrina, answers below...kk
>
> On Tue, Feb 8, 2011 at 6:07 AM, Sabrina Kliegl<skliegl@zitmail.upb.de>  wrote:
>> Hi Kurt,
>>
>> thank you, that is what I was looking for. Maybe you can answer me some
>> questions about the current OpenCV implementation of the block matching:
>>
>> Did I get it right, that you are using a horizontal Sobel filter now
>> instead of the LoG (as mentioned in the paper)? If so, why only a
>> horizontal Sobel filter and no vertical Sobel as well?
>
> X-Sobel gets rid of subpixel error amplification.  See this paper:
>
> Stereo Matching in the Presence of Sub-Pixel Calibration Errors
> Heiko Hirschmu¨ ller, Stefan Gehrig
>
>>
>> Is the block matching applied to the images resulting from the edge
>> detector or to the sharpend original images?
>>
>
> Block matching is applied to the X-Sobel images.
>
>> And I wonder how you achieve subpixel accuracy. I suppose the last
>> magical lines of findStereoCorrespondenceBM(...) to do this:
>>
>> int p = sad[mind+1], n = sad[mind-1], d = p + n - 2*sad[mind] +
>> std::abs(p - n);
>> dptr[y*dstep] = (short)(((ndisp - mind - 1 + mindisp)*256 + (d != 0 ?
>> (p-n)*256/d : 0) + 15)>>  4);
>>
>> But I don't get the idea behind it. Can you give me a hint?
>>
>
> Subpixel interpolation is done by a quadratic interpolation on the min
> correlation value and its two neighbors.  If you work it out, the
> fractional disparity increment is:
>
> (p-n)/(2*(p+n-2*c))
>
> where c is the min correlation value, p is the one preceeding it, and
> n is the one after it.  The OpenCV version mangles this a bit to get
> it into fixed-point form.
>
>> Regards,
>> Sabrina
>>
>> Am 08.02.2011 14:49, schrieb Kurt Konolige:
>>> Sabrina, this is still the best publication I have for this:
>>>
>>> K. Konolige
>>> "Small Vision Systems: hardware and implementation"
>>> Eighth International Symposium on Robotics Research
>>> Hayama, Japan, October 1997
>>>
>>> Cheers --Kurt
>>>
>>> On Tue, Feb 8, 2011 at 1:40 AM, Sabrina Kliegl<skliegl@zitmail.upb.de>    wrote:
>>>> Hi everybody,
>>>>
>>>> I'm using stereo_image_proc in my diploma thesis and I wonder if there
>>>> is any publication of Kurt Konolige (or somebody else) which explains
>>>> the pre- and postfiltering and which I could use as a reference. Thanks!
>>>>
>>>> Regards,
>>>> Sabrina
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