Our journey in experimenting with machine imaginative and prescient and picture recognition accelerated after we had been creating an software, BooksPlus, to vary a reader’s expertise. BooksPlus makes use of picture recognition to convey printed pages to life. A consumer can get immersed in wealthy and interactive content material by scanning photographs within the e book utilizing the BooksPlus app. 

For instance, you possibly can scan an article a couple of poet and immediately take heed to the poet’s audio. Equally, you possibly can scan photographs of historic paintings and watch a documentary clip.

As we began the event, we used commercially accessible SDKs that labored very nicely after we tried to acknowledge photographs regionally. Nonetheless, these would fail as our library of photographs went over just a few hundred photographs. Just a few companies carried out cloud-based recognition, however their pricing construction didn’t match our wants. 

Therefore, we determined to experiment to develop our personal picture recognition answer.

What had been the Targets of our Experiments?

We targeted on constructing an answer that might scale to the 1000’s of photographs that we wanted to acknowledge. Our intention was to attain excessive efficiency whereas being versatile to do on-device and in-cloud picture matching. 

As we scaled the BooksPlus app, the goal was to construct a cheap final result. We ensured that our personal effort was as correct because the SDKs (when it comes to false positives and false adverse matches). Our options wanted to combine with native iOS and Android tasks.

Selecting an Picture Recognition Toolkit

Step one of our journey was to zero down on a picture recognition toolkit. We determined to make use of OpenCV primarily based on the next elements:

  • A wealthy assortment of image-related algorithms: OpenCV has a group of greater than 2500 optimized algorithms, which has many contributions from academia and the trade, making it probably the most important open-source machine imaginative and prescient library.
  • Recognition: OpenCV has an estimated obtain exceeding 18 million and has a neighborhood of 47 thousand customers, making it plentiful technical assist accessible.
  • BSD-licensed product: As OpenCV is BSD-licensed, we are able to simply modify and redistribute it in accordance with our wants. As we wished to white-label this expertise, OpenCV would profit us.
  • C-Interface: OpenCV has C interfaces and assist, which was essential for us as each native iOS and Android assist C; This may enable us to have a single codebase for each the platforms.

The Challenges in Our Journey

We confronted quite a few challenges whereas creating an environment friendly answer for our use case. However first, let’s first perceive how picture recognition works.

What’s Characteristic Detection and Matching in Picture Recognition?

Characteristic detection and matching is an integral part of each pc imaginative and prescient software. It detects an object, retrieve photographs, robotic navigation, and so on. 

Take into account two photographs of a single object clicked at barely totally different angles. How would you make your cellular acknowledge that each the photographs comprise the identical object? Characteristic Detection and Matching comes into play right here.

feature detection and matching for image recognition

A characteristic is a chunk of data that represents if a picture accommodates a particular sample or not. Factors and edges can be utilized as options. The picture above reveals the characteristic factors on a picture. One should choose characteristic factors in a manner that they continue to be invariant below modifications in illumination, translation, scaling, and in-plane rotation. Utilizing invariant characteristic factors is vital within the profitable recognition of comparable photographs below totally different positions.

The First Problem: Gradual Efficiency

After we first began experimenting with picture recognition utilizing OpenCV, we used the really useful ORB characteristic descriptors and FLANN characteristic matching with 2 nearest neighbours. This gave us correct outcomes, but it surely was extraordinarily gradual. 

The on-device recognition labored nicely for just a few hundred photographs; the industrial SDK would crash after 150 photographs, however we had been in a position to enhance that to round 350. Nevertheless, that was inadequate for a large-scale software.

To offer an concept of the velocity of this mechanism, take into account a database of 300 photographs. It might take as much as 2 seconds to match a picture. With this velocity, a database with 1000’s of photographs would take a couple of minutes to match a picture. For the finest UX, the matching have to be real-time, in a blink of an eye fixed. 

The variety of matches made at totally different factors of the pipeline wanted to be minimized to enhance the efficiency. Thus, we had two selections:

  1. Scale back the variety of neighbors close by, however we had solely 2 neighbors: the least doable variety of neighbors.
  2. Scale back the variety of options we detected in every picture, however decreasing the rely would hinder the accuracy. 

We settled upon utilizing 200 options per picture, however the time consumption was nonetheless not passable. 

The Second Problem: Low Accuracy

One other problem that was standing proper there was the lowered accuracy whereas matching photographs in books that contained textual content. These books would generally have phrases across the photographs, which might add many extremely clustered characteristic factors to the phrases. This elevated the noise and lowered the accuracy.

Normally, the e book’s printing brought on extra interference than anything: the textual content on a web page creates many ineffective options, extremely clustered on the sharp edges of the letters inflicting the ORB algorithm to disregard the essential picture options.

The Third Problem: Native SDK

After the efficiency and precision challenges had been resolved, the last word problem was to wrap the answer in a library that helps multi-threading and is appropriate with Android and iOS cellular units.

Our Experiments That Led to the Resolution:

Experiment 1: Fixing the Efficiency Drawback

The target of the primary experiment was to enhance the efficiency. Our engineers got here up with an answer to enhance efficiency. Our system may doubtlessly be offered with any random picture which has billions of prospects and we needed to decide if this picture was a match to our database. Subsequently, as a substitute of doing a direct match, we devised a two-part method: Easy matching and In-depth matching.

Half 1: Easy Matching: 

To start, the system will get rid of apparent non-matches. These are the pictures that may simply be recognized as not matching. They may very well be any of our database’s 1000’s and even tens of 1000’s of photographs. That is completed by a really coarse degree scan that considers solely 20 options by the usage of an on-device database to find out whether or not the picture being scanned belongs to our attention-grabbing set. 

Half 2: In-Depth Matching 

After Half 1, we had been left with only a few photographs with comparable options from a big dataset – the attention-grabbing set. Our second matching step is carried out on these few photographs. An in-depth match was carried out solely on these attention-grabbing photographs. To seek out the matching picture, all 200 options are matched right here. Because of this, we lowered the variety of characteristic matching loops carried out on every picture.

Each characteristic was matched in opposition to each characteristic of the coaching picture. This introduced down the matching loops down from 40,000 (200×200) to 400 (20×20). We’d get a listing of the absolute best matching photographs to additional examine the precise 200 options.

We had been greater than glad with the end result. The dataset of 300 photographs that might beforehand take 2 seconds to match a picture would now take solely 200 milliseconds. This improved mechanism was 10x sooner than the unique, barely noticeable to the human eye in delay.

Experiment 2: Fixing the Scale Drawback

To scale up the system, half 1 of the matching was achieved on the machine and half 2 may very well be achieved within the cloud – this manner, solely photographs that had been a possible match had been despatched to the cloud. We’d ship the 20 characteristic fingerprint match info to the cloud, together with the extra detected picture options. With a big database of attention-grabbing photographs, the cloud may scale.

This methodology allowed us to have a big database (with fewer options) on-device so as to get rid of apparent non-matches. The reminiscence necessities had been lowered, and we eradicated crashes attributable to system useful resource constraints, which was an issue with the industrial SDK. As the true matching was achieved within the cloud, we had been in a position to scale by decreasing cloud computing prices by not utilizing cloud CPU biking for apparent non-matches.

Experiment 3: Bettering the Accuracy

Now that we’ve higher efficiency outcomes, the matching course of’s sensible accuracy wants enhancement. As talked about earlier, when scanning an image in the true world, the quantity of noise was huge.

Our first method was to make use of the CANNY edge detection algorithm to search out the sq. or the rectangle edges of the picture and clip out the remainder of the info, however the outcomes weren’t dependable. We noticed two points that also stood tall. The primary was that the pictures would generally comprise captions which might be part of the general picture rectangle. The second challenge was that the pictures would generally be aesthetically positioned in several shapes like circles or ovals. We would have liked to provide you with a easy answer.

Lastly, we analyzed the pictures in 16 shades of grayscale and tried to search out areas skewed in direction of solely 2 to three shades of gray. This methodology precisely discovered areas of textual content on the outer areas of a picture. After discovering these parts, blurring them would make them dormant in interfering with the popularity mechanism. 

Experiment 4: Implementing a Native SDK for Cell

We swiftly managed to boost the characteristic detection and matching system’s accuracy and effectivity in recognizing photographs. The ultimate step was implementing an SDK that might work throughout each iOS and Android units like it could have been if we carried out them in native SDKs. To our benefit, each Android and iOS assist the usage of C libraries of their native SDKs. Subsequently, a picture recognition library was written in C, and two SDKs had been produced utilizing the identical codebase. 

Every cellular machine has totally different sources accessible. The upper-end cellular units have a number of cores to carry out a number of duties concurrently. We created a multi-threaded library with a configurable variety of threads. The library would robotically configure the variety of threads at runtime as per the cellular machine’s optimum quantity.


To summarize, we developed a large-scale picture recognition software (utilized in a number of fields together with Augmented Actuality) by bettering the accuracy and the effectivity of the machine imaginative and prescient: characteristic detection and matching. The already present options had been gradual and our use case produced noise that drastically lowered accuracy. We desired correct match outcomes inside a blink of an eye fixed.

Thus, we ran just a few checks to enhance the mechanism’s efficiency and accuracy. This lowered the variety of characteristic matching loops by 90%, leading to a 10x sooner match. As soon as we had the efficiency that we desired, we wanted to enhance the accuracy by decreasing the noise across the textual content within the photographs. We had been in a position to accomplish this by blurring out the textual content after analyzing the picture in 16 totally different shades of grayscale. Lastly, every little thing was compiled into the C language library that can be utilized with iOS and Android.

Anand Shah

Ignite Options

Founder and CEO of Ignite Options, Anand Shah is a flexible technologist and entrepreneur. His ardour is backed by 30 years of expertise within the discipline of expertise with a give attention to startups, product administration, ideation, lean strategies, expertise management, buyer relationships, and go-to-market. He serves because the CTO of a number of shopper firms.