All this is take in consideration if we have a single object on the image up to 16.
What will happen is we have repeated objects?
Like the one with multiple cows.
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Yes it’s, but every bit seems “hard-coded” in there. Was wondering if there’s a generator in fastai that can create anchor boxes given an input with parameters like size, ratio etc.
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Ah. Not quite sure about that.!
Thanks! 
What does Pt in the focal loss represent?
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Does focal loss apply to/improve classification in general?
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Is the factor gamma the same for the 4x4 anchor boxes as the 2x2 or the 1x1?
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pt =
p if y = 1
1 − p otherwise
where y is a target and p is an activation.
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Separately, this sounds like we’re saying the background stuff is irrelevant. Have other people tried training a CNN to recognize background, and then remove this from the images? And then run those images with background removed through a classifying CNN for our “real” (non-background) classes? As in, get bounding boxes on stuff that’s just background, and then remove that or black it out, or something.
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In the paper they explain that detecting background is easy, detecting small objects is hard. Focal loss makes the model to focus less on detecting easy stuff (which it will detect well anyway) and more on detecting hard stuff.
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Then it’d be a two-stage approach which might not be the cleanest solution, maybe.
This is exactly what ‘cutting edge’ refers to. Will have to re watch video multiple times and looking forward to @timlee’ s notes 
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I’d love to hear Jeremy’s summary of how computer vision in autonomous vehicles relates to what we’re learning today. (If at all)
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Would you say that focal loss is something one could use for any situation where you have class imbalance? In this case it’s not possible to artificially rebalance the classes, but in cases where that is possible, is focal loss better that resampling/rebalancing?
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Are there any youtube channels where people read through papers like this? I really appreciate this type of walk through.
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You should start one!
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If you start your own, AND start a Patreon account for it too, you might actually get enough Patrons to support you for your time.
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What are we going to look at next week?
Segmentation - carvana
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High level overview
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