Supersonic image recognition for your mobile apps

Cédric @deltheil

Paris Tech Talks #6

Moodstocks

Tech co-founder

Mobile Image Recognition

Your Mobile App

Reference Images + ID-s

Image Recognition Platform

query match ID = 1234

index

user

developer

ID = 1234

The old way: thin client

Mobile App

Image Recognition API

client

server

reference images

send JPEG image via HTTP

match ID or nil

Drawback: network latencies!

Our approach: thick clientMobile App

Moodstocks API

client

server

reference images up to millions images

Moodstocks SDK

image signatures up to 10k images

query match ID or nil

server-side search for large DB

sync

Benefit: speed

a typical search runs in a few ms

Moodstocks SDK

Mobile App

Wrapper

Core Library

Objective-C Java

C

Moodstocks SDK

Mobile App

Wrapper

Core Library

we will now focus on this part

Design Goal #1

Portability• core library written in C99

• +99% code in common between iOS / Android

• e.g supporting Intel CPU-s on Android was… no effort!

Design Goal #2

Efficiency• in-memory data structures for maximum speed

• leverage NEON capabilities (SIMD) where applicable

• a typical search runs in ~ 30 ms / 10k images (iPhone 5S)

Design Goal #3

Low footprint

• 100% home made, lightweight implementation

• implement & embed only what we need!

• around 800 kB for the iOS ARMv7s release build (-Os)

in 1/2 day

Our choices pay off

Core Library Architecture

Public Header File

Internal Modules

3rd Party Libraries

Image Recognition

Pipeline

Public Header File

Internal Modules

3rd Party Libraries

Image Recognition

Pipeline

Image Recognition Pipeline

• full-stack: the whole recognition occurs on-device!

• robust to camera noises (blur, lighting, …)

• supports 1D and 2D barcodes too

Image Recognition Pipeline

Public Header File

Internal Modules

3rd Party Libraries

Image Recognition

Pipeline

Internal Modules (1/4)

• master-slave sync engine for image signatures

• efficient: works with diff-s & data bundles (less requests)

• fail-safe: retries + the client always stays consistent

Sync StorageLogs API client

Internal Modules (2/4)

Sync StorageLogs API client

• collects search results & metadata (OS, etc) along time

• a long-running thread posts batches every 30s

• tolerant to network errors -> HTTP 409 (Already Exists)

Internal Modules (3/4)

• persists image signatures on-disk

• persists search results events on-disk

• used as a temp on-disk buffer at sync time

Sync StorageLogs API client

Internal Modules (4/4)

• used for server-side recognition (send image via HTTP)

• includes a pool to re-use connections

• also used to post logs batches to the server (HTTP)

Sync StorageLogs API client

Public Header File

Internal Modules

3rd Party Libraries

Image Recognition

Pipeline

3rd Party Libraries (1/4)

libcurl Tokyo Cabinet jpec msgpack

• the +500M users file transfer library

• multi API -> multiple transfers in the same thread

• we use it as the backend of our sync engine + HTTP reqs.

3rd Party Libraries (2/4)

libcurl Tokyo Cabinet jpec msgpack

• key / value embedded database (hash / table / B+tree)

• … and also a fantastic C library (see tcutil.h)

• we use it as the backend of our storage engine

3rd Party Libraries (3/4)

libcurl Tokyo Cabinet jpec msgpack

• our home-made, tiny JPEG encoder (600 LOC-s)

• we open sourced it -> github.com/Moodstocks/jpec

• we use it for server-side requests (send image)

3rd Party Libraries (4/4)

libcurl Tokyo Cabinet jpec msgpack

• efficient binary serialization format

• we use it to pack the data we synchronize

Thanks!

Questions? Comments? cedric AT moodstocks DOT com | @deltheil

Building

• we use simple Makefile-s and shell scripts

• we cross-compile w/ the iOS and Android toolchains

• we combine all the arch-s into a fat static lib (armv7, …)

Testing

• we write unit tests with ct (Easy Unit Testing) by @krarick

• we run them on device! e.g jailbreaked iPhone + openssh

• we use a mock to test the sync engine

Quality

• no warnings: we compile with -Wall -Werror

• static analysis with Clang Static Analyzer

• memory leak checks with Valgrind