THREAD: How is it possible to train a well-performing, advanced Computer Vision model ๐—ผ๐—ป ๐˜๐—ต๐—ฒ ๐—–๐—ฃ๐—จ? ๐Ÿค”

At the heart of this lies the most important technique in modern deep learning - transfer learning.

Let's analyze how it

2/ For starters, let's look at what a neural network (NN for short) does.

An NN is like a stack of pancakes, with computation flowing up when we make predictions.

How does it all work?
3/ We show an image to our model.

An image is a collection of pixels. Each pixel is just a bunch of numbers describing its color.

Here is what it might look like for a black and white image
4/ The picture goes into the layer at the bottom.

Each layer performs computation on the image, transforming it and passing it upwards.
5/ By the time the image reaches the uppermost layer, it has been transformed to the point that it now consists of two numbers only.

The outputs of a layer are called activations, and the outputs of the last layer have a special meaning... they are the predictions!
6/ For a NN distinguishing between cats and dogs, when presented with an image of a cat we want the ๐šŒ๐šŠ๐š neuron to light up!

We would like for it to have a high value, and for other activations in the last layer to be small...

So far so good! But what about transfer learning?
7/ Consider the lower levels of our stack of pancakes! This is where the bulk of the computation happens.

We know that these layers evolve during training to become feature detectors.

What do we mean by that?
8/ One layer may have tiny sliding windows that are good at detecting lines.

A layer above might have windows that construct shapes from these lines.

We might have a window light up when it sees a square, another when it sees a colorful blob.
9/ As we move up the stack, the features that windows can detect become more complex, building on the work of the layers below.

Maybe one sliding window will combine lines and detect text... maybe another one will learn to detect faces.

Does all of this sound like a hard task?
10/ Absolutely! A network needs to see a lot of pictures to learn all of that.

But, presumably, once we detect all these lower-level features, we can combine them in a plethora of interesting ways? ๐Ÿค”
11/ We can take all the lines, and the blobs, and the faces, or whatever the lower layers of the network can see, and combine them to predict cats and dogs!

Or trains, planes, and ships. Or blood cell boundaries. Or aneurysms in x-rays. The possibilities are endless!
12/ This is precisely what transfer learning is!

We let researchers, large corporations, spend millions of dollars to train very complex models.

And then we get to build on top of their work! ๐Ÿ˜‡

But so much for the theory. How does it all work in practice?
13/ In our example, we took a pretrained model that was trained on a subset of Imagenet consisting of 1.2 million images across 1000 classes!

The @fastdotai framework downloaded the model for us and removed the top of it (the part responsible for predicting 1 of 1000 classes).
14/ It created a new head for our model, one tailored to the classes in the new dataset.

During training, we kept nearly the entire model frozen, and only trained the uppermost part, making use of all the lower level features that were being detected.

Ingenius! ๐Ÿ˜
15/ The concept of transfer learning, of utilizing a model trained on one task to perform another one, applies to other scenarios as well, including NLP (models that act on text).

We will hopefully get a chance to explore all of them ๐Ÿ™‚
16/ I plan to explain all the concepts in modern AI in a similar fashion, assuming people find this useful ๐Ÿ™‚

If you enjoyed this thread, let me know please and help me reach others who might also be interested ๐Ÿ˜Š๐Ÿ™

And the visualizations of what the layers can detect?
17/ They come from this seminal paper - Visualizing and Understanding Convolutional Networks https://t.co/c3DMSTMc4T

Next stop - deciphering how it all works in code and finding ways to further improve our model!

Stay tuned for more ๐Ÿ™‚

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The YouTube algorithm that I helped build in 2011 still recommends the flat earth theory by the *hundreds of millions*. This investigation by @RawStory shows some of the real-life consequences of this badly designed AI.


This spring at SxSW, @SusanWojcicki promised "Wikipedia snippets" on debated videos. But they didn't put them on flat earth videos, and instead @YouTube is promoting merchandising such as "NASA lies - Never Trust a Snake". 2/


A few example of flat earth videos that were promoted by YouTube #today:
https://t.co/TumQiX2tlj 3/

https://t.co/uAORIJ5BYX 4/

https://t.co/yOGZ0pLfHG 5/
"I really want to break into Product Management"

make products.

"If only someone would tell me how I can get a startup to notice me."

Make Products.

"I guess it's impossible and I'll never break into the industry."

MAKE PRODUCTS.

Courtesy of @edbrisson's wonderful thread on breaking into comics โ€“
https://t.co/TgNblNSCBj โ€“ here is why the same applies to Product Management, too.


There is no better way of learning the craft of product, or proving your potential to employers, than just doing it.

You do not need anybody's permission. We don't have diplomas, nor doctorates. We can barely agree on a single standard of what a Product Manager is supposed to do.

But โ€“ there is at least one blindingly obvious industry consensus โ€“ a Product Manager makes Products.

And they don't need to be kept at the exact right temperature, given endless resource, or carefully protected in order to do this.

They find their own way.
What an amazing presentation! Loved how @ravidharamshi77 brilliantly started off with global macros & capital markets, and then gradually migrated to Indian equities, summing up his thesis for a bull market case!

@MadhusudanKela @VQIndia @sameervq

My key learnings: โฌ‡๏ธโฌ‡๏ธโฌ‡๏ธ


First, the BEAR case:

1. Bitcoin has surpassed all the bubbles of the last 45 years in extent that includes Gold, Nikkei, dotcom bubble.

2. Cyclically adjusted PE ratio for S&P 500 almost at 1929 (The Great Depression) peaks, at highest levels except the dotcom crisis in 2000.

3. World market cap to GDP ratio presently at 124% vs last 5 years average of 92% & last 10 years average of 85%.
US market cap to GDP nearing 200%.

4. Bitcoin (as an asset class) has moved to the 3rd place in terms of price gains in preceding 3 years before peak (900%); 1st was Tulip bubble in 17th century (rising 2200%).

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