Blog
The latest news from Google AI
Self-Supervised Tracking via Video Colorization
Wednesday, June 27, 2018
Posted by Carl Vondrick, Research Scientist, Machine Perception
Tracking objects in video is a fundamental problem in computer vision, essential to applications such as
activity recognition
,
object interaction
, or
video stylization
. However, teaching a machine to visually track objects is challenging partly because it requires large, labeled tracking datasets for training, which are impractical to annotate at scale.
In “
Tracking Emerges by Colorizing Videos
”, we introduce a convolutional network that colorizes grayscale videos, but is constrained to copy colors from a single reference frame. In doing so, the network learns to visually track objects automatically without supervision. Importantly, although the model was never trained explicitly for tracking, it can follow multiple objects, track through occlusions, and remain robust over deformations without requiring
any
labeled training data.
Example tracking predictions on the publicly-available, academic dataset
DAVIS 2017
. After learning to colorize videos, a mechanism for tracking automatically emerges without supervision. We specify regions of interest (indicated by different colors) in the first frame, and our model propagates it forward without any additional learning or supervision.
Learning to Recolorize Video
Our hypothesis is that the temporal coherency of color provides excellent large-scale training data for teaching machines to track regions in video. Clearly, there are exceptions when color is not temporally coherent (such as lights turning on suddenly), but in general color is stable over time. Furthermore, most videos contain color, providing a scalable self-supervised learning signal. We decolor videos, and then add the colorization step because there may be multiple objects with the same color, but by colorizing we can teach machines to track specific objects or regions.
In order to train our system, we use videos from the
Kinetics dataset
, which is a large public collection of videos depicting everyday activities. We convert all video frames except the first frame into gray-scale, and train a convolutional network to predict the original colors in the subsequent frames. We expect the model to learn to follow regions in order to accurately recover the original colors. Our main observation is the need to follow objects for colorization will cause a model for object tracking to be automatically learned.
We illustrate the video recolorization task using video from
the DAVIS 2017 dataset
. The model receives as input one color frame and a gray-scale video, and predicts the colors for the rest of the video. The model learns to copy colors from the reference frame, which enables a mechanism for tracking to be learned without human supervision.
Learning to copy colors from the single reference frame requires the model to learn to internally point to the right region in order to copy the right colors. This forces the model to learn an explicit mechanism that we can use for tracking. To see how the video colorization model works, we show some predicted colorizations from videos in the Kinetics dataset below.
Examples of predicted colors from colorized reference frame applied to input video using the publicly-available
Kinetics dataset
.
Although the network is trained without ground-truth identities, our model learns to track any visual region specified in the first frame of a video. We can track outlined objects or a single point in the video. The only change we make is that, instead of propagating colors throughout the video, we now propagate labels representing the regions of interest.
Analyzing the Tracker
Since the model is trained on large amounts of unlabeled video, we want to gain insight into what the model learns. The videos below show a standard trick to visualize the embeddings learned by our model by projecting them down to three dimensions using
Principal Component Analysis
(PCA) and plotting it as an RGB movie. The results show that nearest neighbors in the learned embedding space tend to correspond to object identity, even over deformations and viewpoint changes.
Top Row: We show videos from the
DAVIS 2017 dataset
. Bottom Row: We visualize the internal embeddings from the colorization model. Similar embeddings will have a similar color in this visualization. This suggests the learned embedding is grouping pixels by object identity.
Tracking Pose
We found the model can also track human poses given key-points in an initial frame. We show results on the publicly-available, academic dataset
JHMDB
where we track a human joint skeleton.
Examples of using the model to track movements of the human skeleton. In this case the input was a human pose for the first frame and subsequent movement is automatically tracked. The model can track human poses even though it was never explicitly trained for this task.
While we do not yet outperform heavily supervised models, the colorization model learns to track video segments and human pose well enough to outperform the
latest methods
based on
optical flow
. Breaking down performance by motion type suggests that our model is a more robust tracker than optical flow for many natural complexities, such as dynamic backgrounds, fast motion, and occlusions. Please see
the paper
for details.
Future Work
Our results show that video colorization provides a signal that can be used for learning to track objects in videos without supervision. Moreover, we found that the failures from our system are correlated with failures to colorize the video, which suggests that further improving the video colorization model can advance progress in self-supervised tracking.
Acknowledgements
This project was only possible thanks to several collaborations at Google. The core team includes Abhinav Shrivastava, Alireza Fathi, Sergio Guadarrama and Kevin Murphy. We also thank David Ross, Bryan Seybold, Chen Sun and Rahul Sukthankar.
Labels
accessibility
ACL
ACM
Acoustic Modeling
Adaptive Data Analysis
ads
adsense
adwords
Africa
AI
AI for Social Good
Algorithms
Android
Android Wear
API
App Engine
App Inventor
April Fools
Art
Audio
Augmented Reality
Australia
Automatic Speech Recognition
AutoML
Awards
BigQuery
Cantonese
Chemistry
China
Chrome
Cloud Computing
Collaboration
Compression
Computational Imaging
Computational Photography
Computer Science
Computer Vision
conference
conferences
Conservation
correlate
Course Builder
crowd-sourcing
CVPR
Data Center
Data Discovery
data science
datasets
Deep Learning
DeepDream
DeepMind
distributed systems
Diversity
Earth Engine
economics
Education
Electronic Commerce and Algorithms
electronics
EMEA
EMNLP
Encryption
entities
Entity Salience
Environment
Europe
Exacycle
Expander
Faculty Institute
Faculty Summit
Flu Trends
Fusion Tables
gamification
Gboard
Gmail
Google Accelerated Science
Google Books
Google Brain
Google Cloud Platform
Google Docs
Google Drive
Google Genomics
Google Maps
Google Photos
Google Play Apps
Google Science Fair
Google Sheets
Google Translate
Google Trips
Google Voice Search
Google+
Government
grants
Graph
Graph Mining
Hardware
HCI
Health
High Dynamic Range Imaging
ICCV
ICLR
ICML
ICSE
Image Annotation
Image Classification
Image Processing
Inbox
India
Information Retrieval
internationalization
Internet of Things
Interspeech
IPython
Journalism
jsm
jsm2011
K-12
Kaggle
KDD
Keyboard Input
Klingon
Korean
Labs
Linear Optimization
localization
Low-Light Photography
Machine Hearing
Machine Intelligence
Machine Learning
Machine Perception
Machine Translation
Magenta
MapReduce
market algorithms
Market Research
Mixed Reality
ML
ML Fairness
MOOC
Moore's Law
Multimodal Learning
NAACL
Natural Language Processing
Natural Language Understanding
Network Management
Networks
Neural Networks
NeurIPS
Nexus
Ngram
NIPS
NLP
On-device Learning
open source
operating systems
Optical Character Recognition
optimization
osdi
osdi10
patents
Peer Review
ph.d. fellowship
PhD Fellowship
PhotoScan
Physics
PiLab
Pixel
Policy
Professional Development
Proposals
Public Data Explorer
publication
Publications
Quantum AI
Quantum Computing
Recommender Systems
Reinforcement Learning
renewable energy
Research
Research Awards
resource optimization
Robotics
schema.org
Search
search ads
Security and Privacy
Self-Supervised Learning
Semantic Models
Semi-supervised Learning
SIGCOMM
SIGMOD
Site Reliability Engineering
Social Networks
Software
Sound Search
Speech
Speech Recognition
statistics
Structured Data
Style Transfer
Supervised Learning
Systems
TensorBoard
TensorFlow
TPU
Translate
trends
TTS
TV
UI
University Relations
UNIX
Unsupervised Learning
User Experience
video
Video Analysis
Virtual Reality
Vision Research
Visiting Faculty
Visualization
VLDB
Voice Search
Wiki
wikipedia
WWW
Year in Review
YouTube
Archive
2021
Jul
Jun
May
Apr
Mar
Feb
Jan
2020
Dec
Nov
Oct
Sep
Aug
Jul
Jun
May
Apr
Mar
Feb
Jan
2019
Dec
Nov
Oct
Sep
Aug
Jul
Jun
May
Apr
Mar
Feb
Jan
2018
Dec
Nov
Oct
Sep
Aug
Jul
Jun
May
Apr
Mar
Feb
Jan
2017
Dec
Nov
Oct
Sep
Aug
Jul
Jun
May
Apr
Mar
Feb
Jan
2016
Dec
Nov
Oct
Sep
Aug
Jul
Jun
May
Apr
Mar
Feb
Jan
2015
Dec
Nov
Oct
Sep
Aug
Jul
Jun
May
Apr
Mar
Feb
Jan
2014
Dec
Nov
Oct
Sep
Aug
Jul
Jun
May
Apr
Mar
Feb
Jan
2013
Dec
Nov
Oct
Sep
Aug
Jul
Jun
May
Apr
Mar
Feb
Jan
2012
Dec
Oct
Sep
Aug
Jul
Jun
May
Apr
Mar
Feb
Jan
2011
Dec
Nov
Sep
Aug
Jul
Jun
May
Apr
Mar
Feb
Jan
2010
Dec
Nov
Oct
Sep
Aug
Jul
Jun
May
Apr
Mar
Feb
Jan
2009
Dec
Nov
Aug
Jul
Jun
May
Apr
Mar
Feb
Jan
2008
Dec
Nov
Oct
Sep
Jul
May
Apr
Mar
Feb
2007
Oct
Sep
Aug
Jul
Jun
Feb
2006
Dec
Nov
Sep
Aug
Jul
Jun
Apr
Mar
Feb
Feed
Follow @googleai
Give us feedback in our
Product Forums
.
