AI Generates Realistic 3D Models Using Only a Handful of Images

Neural Rendering is the ability to generate a photorealistic model in space just like this one, from pictures of the object, person, or scene of interest. In this case, you’d have a handful of pictures of this sculpture and ask the machine to understand what the object in these pictures should look like in space.

You are basically asking a machine to understand physics and shapes out of images. This is quite easy for us since we only know the real world and depths, but it’s a whole other challenge for a machine that only sees pixels.

It’s great that the generated model looks accurate with realistic shapes, but what about how it blends in the new scene?

And what if the lighting conditions vary in the pictures taken and the generated model looks different depending on the angle you look at it?

This would automatically seem weird and unrealistic to us. These are the challenges Snapchat and the University of Southern California attacked in this new research.

Watch to learn more:

References:

►Read the full article: https://www.louisbouchard.ai/neroic/
►Kuang, Z., Olszewski, K., Chai, M., Huang, Z., Achlioptas, P. and
Tulyakov, S., 2022. NeROIC: Neural Rendering of Objects from Online
Image Collections. https://arxiv.org/pdf/2201.02533.pdf
►Project link with great video demo: https://formyfamily.github.io/NeROIC/
►Code: https://github.com/snap-research/NeROIC
►My Newsletter (A new AI application explained weekly to your emails!): https://www.louisbouchard.ai/newsletter/

Video Transcript

       00:00

neural rendering neural rendering is the

00:03

ability to generate a photorealistic

00:05

model in space just like this one from

00:07

pictures of the object person or scene

00:10

of interest in this case you'll have a

00:13

handful of pictures of this sculpture

00:15

and ask the machine to understand what

00:17

the object in these pictures should look

00:19

like in space you are basically asking a

00:21

machine to understand physics and shapes

00:23

out of images this is quite easy for us

00:26

since we only know the real world and

00:28

depth but it's a whole other challenge

00:30

for a machine that only sees pixels then

00:33

you might ask why do we even want to do

00:35

this i'd say that the answer is pretty

00:37

obvious to me there are many cool

00:39

applications from having an app that

00:41

could simply take a few pictures of an

00:43

object and perfectly synthesize the 3d

00:45

model to put it in images 3d scenes or

00:48

even video games this is really

00:50

promising but for these models to be

00:52

realistic lighting is another challenge

00:54

that comes with these applications it's

00:56

great that the generated model looks

00:58

accurate with realistic shapes but what

01:00

about how it blends in the new scene and

01:02

what if the lighting conditions vary in

01:05

the pictures taken and the generated

01:07

model looks different depending on the

01:09

angle you look at it this will

01:11

automatically seem weird and unrealistic

01:13

to us these are the challenges snapchat

01:15

and the university of southern

01:17

california attacked in this new research

01:19

but first a word from this episode

01:21

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01:24

biases allows you to easily keep track

01:26

of the input hyperparameters output

01:28

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01:30

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01:32

lines added to your code one aspect

01:34

that's great for speeding up your

01:36

experiments is sweeps sweeps automate

01:38

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01:40

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01:42

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01:45

run all tests tweaking the parameters

01:47

and reporting the effect of all

01:48

parameters in clear graphs and reports

01:51

you can share with your team to explain

01:53

your final results easily i love to do

01:55

my best trying to make research look

01:57

simple and clear for you all and this is

01:59

a big reason why i love weights and

02:01

biases they are doing the same thing

02:04

with their platform making your research

02:06

look simple and reproducible i'd love

02:09

for you to check them out with the first

02:10

link below because they are helping me

02:12

continue making these videos and growing

02:14

this channel

02:16

now let's see how these researchers

02:17

tackle the lighting and realism

02:19

challenges that come with creating a

02:21

virtual object out of images the

02:23

technique builds upon neural radiance

02:25

fields which are largely used for

02:27

reconstruction with many models such as

02:30

nerf that we already covered on the

02:32

channel typically neural regions fields

02:34

need images taken in the same ideal

02:37

conditions but this is not what we want

02:39

here their approach starts with nerf and

02:42

as i said i already covered it on my

02:44

channel so i won't cover it again but

02:46

feel free to take a break and watch the

02:47

video to better understand how nerf

02:50

works in short nerf is a neural network

02:52

that is trained to infer the color

02:54

opacity and radiance of each pixel using

02:57

the images as inputs and guess the

03:00

missing pixels for the small parts of

03:02

the objects that aren't present in the

03:04

images but this approach doesn't work

03:06

for large missing parts or different

03:08

lighting conditions as it can only

03:10

interpolate from the input images here

03:13

we need something more to extrapolate

03:16

from it and make assumptions on what

03:18

should appear here and there or how

03:20

these pixels should look like under this

03:22

lighting or that one many approaches

03:25

build upon nerf to fix this but always

03:27

require more inputs from the user which

03:30

is not what we want and is hard to have

03:32

in many cases especially when we want to

03:34

build a good data set to train our model

03:37

on in short these models do not really

03:39

understand the object nor the

03:41

environment the object is in so we

03:43

always come back to the lighting problem

03:46

here the goal is to use this

03:47

architecture in online images or in

03:50

other words images with varying lighting

03:52

cameras environments and poses something

03:55

nerf can hardly do with realism the only

03:59

few things they will need other than the

04:01

images of the object themselves are a

04:03

rough foreground segmentation and an

04:06

estimation of the camera parameters

04:08

which can both be obtained with other

04:10

models available the foreground

04:12

estimation is basically just a mask that

04:14

tells you where the object of interest

04:17

is in your image like this

04:19

what they did differently is that they

04:21

separate the rendering of the object

04:23

from the environment lighting in the

04:25

input images they focus on two things

04:28

which are done in two stages first is

04:30

the object's shape or its geometry which

04:33

is the part that is most similar to nerf

04:35

here called the geometry network it will

04:38

take the input images segmentation mask

04:40

and camera parameters estimation we

04:42

discussed build a radiance field and

04:44

find the first guess of the density and

04:46

colors of each pixel as in nerf but

04:49

adapt with varying lighting conditions

04:51

in the input images this difference

04:53

relies on the two branches you see here

04:55

splitting the static content from the

04:57

varying parameters like camera or

04:59

shadows this will allow us to teach our

05:02

model how to correctly isolate the

05:04

static content from other unwanted

05:06

parameters like lighting but we are not

05:08

finished here we will estimate the

05:10

surface normals from this learned

05:13

density field which will be our textures

05:16

or in other words it will take the

05:18

results we just produced and find how

05:20

our object will react to light it will

05:23

find unbiased material properties of the

05:25

object at this stage or at least an

05:28

estimation of it using a 3d convolution

05:31

with a sobol kernel it's basically a

05:33

filter that we apply in three dimensions

05:35

to find all edges and how sharp they are

05:38

which can look like this on a

05:40

two-dimensional image and this on a

05:42

three-dimensional rendering giving us

05:44

essential information about the

05:46

different textures and shapes of the

05:48

object

05:49

the next stage is where they will fix

05:51

the long geometry and optimize the

05:53

normals we just produced using the

05:55

rendering network which is very similar

05:57

to the first geometry network here again

05:59

there are two branches one for the

06:01

material and another for the lighting

06:03

they will use spherical harmonics to

06:06

represent the lighting model and

06:08

optimize its coefficients during

06:09

training as they explain in the paper

06:11

with more information if you are

06:13

interested spherical harmonics are used

06:15

here to represent a group of basis

06:17

functions defined on the sphere surface

06:20

we can find on wikipedia that each

06:22

function defined on the surface of a

06:24

sphere can be written as a sum of these

06:27

spherical harmonics this technique is

06:29

often used for calculating the lighting

06:31

on 3d models it produces highly

06:34

realistic shading and shadowing with

06:36

comparatively little overhead in short

06:39

it will simply reduce the number of

06:40

parameters to estimate but keep the same

06:42

amount of information so instead of

06:44

learning how to render the appropriate

06:46

lighting for the whole object from

06:48

scratch the model will instead be

06:50

learning the correct coefficients to use

06:52

in the spherical harmonics that will

06:54

estimate the lighting coming out of the

06:56

surface of each pixel simplifying the

06:58

problem to a few parameters the other

07:00

branch will be trained to improve the

07:02

surface normals of the object following

07:04

the same trick using the standard foam

07:06

brdf which will model the object

07:09

material properties based on a few

07:11

parameters to find finally the outputs

07:13

of the two branches so the final

07:15

rendering and lighting will be merged to

07:18

find the final color of each pixel this

07:20

disentanglement of light and materials

07:23

is why they are able to apply any

07:25

lighting to the object and have it react

07:27

realistically remember this is done

07:30

using only a couple of images from the

07:32

internet and could all have different

07:34

lighting conditions this is amazing and

07:37

voila this is how this new paper from

07:40

quang and collaborators at snapchat

07:42

created neroic a neural rendering model

07:45

for objects from online images i hope

07:47

you enjoyed this short overview of the

07:49

paper all the references are linked

07:51

below as well as a link to the official

07:54

project and their code let me know what

07:56

you think of the explanation the

07:57

technique and how do you use it in the

08:00

real world if you are still here and

08:02

enjoy the video please don't forget to

08:04

leave a like and subscribe to the

08:06

channel it both means a lot and helps a

08:08

lot thank you for watching