Blog
The latest from Google Research
Lens Blur in the new Google Camera app
Wednesday, April 16, 2014
Posted by Carlos Hernández, Software Engineer
One of the biggest advantages of
SLR cameras
over camera phones is the ability to achieve shallow depth of field and
bokeh
effects. Shallow depth of field makes the object of interest "pop" by bringing the foreground into focus and de-emphasizing the background. Achieving this optical effect has traditionally required a big lens and aperture, and therefore hasn’t been possible using the camera on your mobile phone or tablet.
That all changes with
Lens Blur,
a new mode in the
Google Camera
app. It lets you take a photo with a shallow depth of field using just your Android phone or tablet. Unlike a regular photo, Lens Blur lets you change the point or level of focus
after
the photo is taken. You can choose to make any object come into focus simply by tapping on it in the image. By changing the depth-of-field slider, you can simulate different aperture sizes, to achieve bokeh effects ranging from subtle to surreal (e.g.,
tilt-shift
). The new image is rendered instantly, allowing you to see your changes in real time.
Lens Blur replaces the need for a large optical system with algorithms that
simulate
a larger lens and aperture. Instead of capturing a single photo, you move the camera in an upward sweep to capture a whole series of frames. From these photos, Lens Blur uses computer vision algorithms to create a 3D model of the world, estimating the
depth
(distance) to every point in the scene. Here’s an example -- on the left is a raw input photo, in the middle is a “depth map” where darker things are close and lighter things are far away, and on the right is the result blurred by distance:
Here’s how we do it. First, we pick out visual features in the scene and track them over time, across the series of images. Using computer vision algorithms known as Structure-from-Motion (SfM) and
bundle adjustment
, we compute the camera’s 3D position and orientation and the 3D positions of all those image features throughout the series.
Once we’ve got the 3D pose of each photo, we compute the depth of each pixel in the reference photo using
Multi-View Stereo
(MVS) algorithms. MVS works the way human stereo vision does: given the location of the same object in two different images, we can
triangulate
the 3D position of the object and compute the distance to it. How do we figure out which pixel in one image corresponds to a pixel in another image? MVS measures how similar they are -- on mobile devices, one particularly simple and efficient way is computing the Sum of Absolute Differences (SAD) of the RGB colors of the two pixels.
Now it’s an optimization problem: we try to build a depth map where all the corresponding pixels are most similar to each other. But that’s typically not a well-posed optimization problem -- you can get the same similarity score for different depth maps. To address this ambiguity, the optimization also incorporates assumptions about the 3D geometry of a scene, called a "prior,” that favors reasonable solutions. For example, you can often assume two pixels near each other are at a similar depth. Finally, we use
Markov Random Field
inference methods to solve the optimization problem.
Having computed the depth map, we can re-render the photo, blurring pixels by differing amounts depending on the pixel’s depth, aperture and location relative to the focal plane. The focal plane determines which pixels to blur, with the amount of blur increasing proportionally with the distance of each pixel to that focal plane. This is all achieved by simulating a physical lens using the
thin lens
approximation.
The algorithms used to create the 3D photo run entirely on the mobile device, and are closely related to the computer vision algorithms used in 3D mapping features like Google Maps
Photo Tours
and
Google Earth
. We hope you have fun with your
bokeh
experiments!
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
materials science
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
Responsible AI
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
2022
May
Apr
Mar
Feb
Jan
2021
Dec
Nov
Oct
Sep
Aug
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
.
