[Kwiver-users] Bounding box coordinates

[Paul Tunison]

I don't remember the name, but the process could be constrained to only
allow the type of transform that allows translation and scaling (no
rotation, etc.).

On Mon, Mar 12, 2018 at 10:59 AM, Matt Brown <matt.brown at kitware.com> wrote:

> I have an application where I would like to significantly reduce the
> resolution of an image using pyramid reductions, run a detector on that
> reduced-resolution image, and then warp the resulting bounding box back up
> to the native-resolution coordinate system. However, I have some questions
> about dealing with the bounding box coordinates and how detectors treat, or
> should treat, these coordinates.
>
> I wrote a new OCV image_pyramid process, which can be configured to apply
> multiple iterations of OCV's pyrUp or pyDown and can emit a homography
> (there is actually a 0.5 pixel translation on each level, so it's not just
> a scaling) representing the warping from output image back to source image.
> I am also writing a *detected_object_bounding_box_warp* node to apply a
> homography to each bounding box in a detected_object_set. Basically, it
> will warp the top-left and bottom-left coordinates with the homography.
> Though, I admit it is a little weird applying a homography to a bounding
> box that has to remain an axis-aligned rectangle. So, maybe there is a
> discussion about renaming or reworking this.
>
> My question is related to the precise definition of the bounding box,
> which encodes the upper left and lower right coordinates of the box. Do we
> have a standard enforced for how detectors populate these bounding boxes?
> Let's say you have a detection covering a rectangle of pixels starting at
> upper-left pixel indices (x1,y1) to lower-right (x2,y2) inclusive, I would
> think the bounding box definition should be (x1-0.5,y1-0.5) to lower-right
> (x2+0.5,y2+0.5), which is the box in image coordinates completely
> containing the area of the pixels. A different of a half pixel may seem
> trivial, but in my case, I am detecting on a highly reduced version of the
> image and then upscaling the bounding boxes, so that half pixel of
> different can be compounded many times.
>
> Thanks,
> Matt
>
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>


-- 
Paul Tunison
Senior R&D Engineer
Kitware, Inc.
28 Corporate Drive
Clifton Park, NY 12065 USA

Phone: (518) 371-3971 Ext.164
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