Masks

[david...@gmail.com]

Looking at documentation for sift in opencv I see that it is possible to pass a mask to exclude parts of an image. Does colmap have this ability? For instance to exclude specular reflections?

Forgive me if the question is redundant or off topic. This is my second day since discovering SfM.

[Johannes Schönberger]

Hi David,

Currently, there is no option to provide a mask in COLMAP but it should be relatively easy to implement. Alternatively, you can compute features using OpenCV and import those features into COLMAP, as described in the documentation. Since this came up before, I might consider implementing such a feature soon. I will keep track of it here https://github.com/colmap/colmap/issues/208

Thanks for the feedback and let me know if you have other questions. 

Best,

Johannes

On 23 Aug 2017, at 20:49, david...@gmail.com wrote:

Looking at documentation for sift in opencv I see that it is possible to pass a mask to exclude parts of an image. Does colmap have this ability? For instance to exclude specular reflections?

Forgive me if the question is redundant or off topic. This is my second day since discovering SfM.

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[david...@gmail.com]

Hi Johannes,

Thanks for the speedy response!

I've had some fun implementing this feature myself. I'm not sure if my solution is what you had in mind. I made the changes as unobtrusive as possible, adding a separate data member to the Bitmap class, "alpha_", which contains a greyscale FIBitmapPtr for images that have alpha channels. Plus some extra functions to deal with that stuff, and a function in base/feature_extraction.cc to filter/resize the Keypoints vector and Descriptor matrix.

Seems to work :)

[Johannes Schönberger]

Hi David,

this sounds great. I am not sure if I am going to incorporate it and I might not get around looking at it for a while (due to other projects) but do you have the code online somewhere?

Thanks for the feedback.

Best,
Johannes

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[David DeWert]

Hi Johannes,

So I submitted a pull request but deleted it. Merge conflicts.

I guess the basic question is how useful is this, really? And is it worth making changes in basic classes like colmap::Bitmap? And is the best solution to remove SIFT features, or to tag them in some way?

It would be worth the trouble if there were good algorithms for identifying specular reflections in still images, but that seems to be a challenge (?)

This is interesting and uses SIFT, "Reflection Detection in Image Sequences":
http://www.mee.tcd.ie/~sigmedia/pmwiki/uploads/Misc.Icip2011/CVPR_new.pdf

[david...@gmail.com]

Okay here is the code, if you're interested:

https://github.com/colmap/colmap/compare/dev...ddewert:iss208

[Johannes Schönberger]

Thanks David. I will try to have a look over the next days/weeks - I am currently a little busy with deadlines.

Cheers, Johannes

> On Oct 16, 2017, at 2:12 AM, david...@gmail.com wrote:
>
> Okay here is the code, if you're interested:
>
> https://github.com/colmap/colmap/compare/dev...ddewert:iss208
>
>
>

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[gus...@laserpanda.com]

I would definitely find this useful, in fact it is a make or break functionality for me.

[Roberto Colella]

Hi,

Should mask_path be provided as a parameter or colmap looks for masks in the .png format in a folder at the same level as images one?

Roberto