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Deep Learning for Computer Vision:

The Abridged Guide

Deep Learning for Computer Vision

Computer vision (CV) is the scientific field which defines how machines interpret the meaning of images and videos. Computer vision algorithms analyze certain criteria in images and videos, and then apply interpretations to predictive or decision making tasks.

Today, deep learning techniques are most commonly used for computer vision. This article explores different ways you can use deep learning for computer vision. In particular, you will learn about the advantages of using convolutional neural networks (CNNs), which provide a multi-layered architecture that allows neural networks to focus on the most relevant features in the image. 

In this article, you will learn:

What Is Computer Vision?

Computer vision is an area of machine learning dedicated to interpreting and understanding images and video. It is used to help teach computers to “see” and to use visual information to perform visual tasks that humans can.

Computer vision models are designed to translate visual data based on features and contextual information identified during training. This enables models to interpret images and video and apply those interpretations to predictive or decision making tasks. 

Although both related to visual data, image processing is not the same as computer vision. Image processing involves modifying or enhancing images to produce a new result. It can include optimizing brightness or contrast, increasing resolution, blurring sensitive information, or cropping. The difference between image processing and computer vision is that the former doesn’t necessarily require the identification of content. 

Convolutional Neural Networks: The Foundation of Modern Computer Vision

Modern computer vision algorithms are based on convolutional neural networks (CNNs), which provide a dramatic improvement in performance compared to traditional image processing algorithms. 

CNNs are neural networks with a multi-layered architecture that is used to gradually reduce data and calculations to the most relevant set. This set is then compared against known data to identify or classify the data input. 

CNNs are typically used for computer vision tasks although text analytics and audio analytics can also be performed. One of the first CNN architectures was AlexNet (described below), which won the ImageNet visual recognition challenge in 2012.

How CNNs work

When an image is processed by a CNN, each base color used in the image (e.g. red, green, blue) is represented as a matrix of values. These values are evaluated and condensed into 3D tensors (in the case of color images), which are collections of stacks of feature maps tied to a section of the image. 

These tensors are created by passing the image through a series of convolutional and pooling layers, which are used to extract the most relevant data from an image segment and condense it into a smaller, representative matrix. This process is repeated numerous times (depending on the number of convolutional layers in the architecture). The final features extracted by the convolutional process are sent to a fully connected layer, which generates predictions. 

Deep Learning Architectures for Computer Vision

The performance and efficiency of a CNN is determined by its architecture. This includes the structure of layers, how elements are designed, and which elements are present in each layer. Many CNNs have been created, but the following are some of the most effective designs.

AlexNet (2012)

AlexNet

AlexNet is an architecture based on the earlier LeNet architecture. It includes five convolutional layers and three fully connected layers. AlexNet uses a dual pipeline structure to accommodate the use of two GPUs during training. 

Learn more in our GPU guide, which reviews the best GPUs for deep learning

The main difference between AlexNet and previous architectures is its use of rectified linear units (ReLU) instead of sigmoid or Tanh activation functions which were used in traditional neural networks. ReLU is simpler and faster to compute, enabling AlexNet to train models faster. 

GoogleNet (2014)

GoogleNet, also known as Inception V1, is based on the LeNet architecture. It is made up of 22 layers made up of small groups of convolutions, called “inception modules”. These inception modules use batch normalization and RMSprop to reduce the number of parameters GoogleNet needs to process. RMSprop is an algorithm that uses adaptive learning rate methods.

VGGNet (2014)

VGG 16 is a 16 layer architecture (some variants had 19 layers). VGGNet has convolutional layers, a pooling layer, a few more convolutional layers, a pooling layer, several more conv layers and so on. 

VGG is based on the notion of a much deeper network with smaller filters – it uses 3×3 convolutions all the way, which is the smallest conv filter size that only looks at some of the neighbouring pixels. It uses small filters because of fewer parameters, making it possible to add more layers. It has the same effective receptive field as if you have one 7×7 convolutional layer.

ResNet (2015)

ResNet, short for Residual Neural Network, is an architecture designed to have a large number of layers – typically used architectures range from ResNet-18 (with 18 layers) to ResNet-1202 (with 1202 layers).These layers are set up with gated units or “skip connections” which enable it to pass information to later convolutional layers. ResNet also employs batch normalization to improve the stability of the network. 

Xception (2016)

Xception is an architecture based on Inception, that replaces the inception modules with depthwise separable convolutions (depthwise convolution followed by pointwise convolutions). It works by first capturing cross-feature map correlations and then spatial correlations. This enables more efficient use of model parameters. 

ResNeXt-50 (2017)

ResNeXt-50

ResNeXt-50 is an architecture based on modules with 32 parallel paths. It uses cardinality to decrease validation errors and represents a simplification of the inception modules used in other architectures. 

Uses of Deep Learning in Computer Vision

The development of deep learning technologies has enabled the creation of more accurate and complex computer vision models. As these technologies increase, the incorporation of computer vision applications is becoming more useful. Below are a few ways deep learning is being used to improve computer vision.

Object detection

There are two common types of object detection performed via computer vision techniques:

  • Two-step object detection – the first step requires a Region Proposal Network (RPN), providing a number of candidate regions that may contain important objects. The second step is passing region proposals to a neural classification architecture, commonly an RCNN-based hierarchical grouping algorithm, or region of interest (ROI) pooling in Fast RCNN. These approaches are quite accurate, but can very slow.
  • One-step object detection – with the need for real time object detection, one-step object detection architectures have emerged, such as YOLO, SSD, and RetinaNet. These combine the detection and classification step, by regressing bounding box predictions. Every bounding box is represented with just a few coordinates, making it easier to combine the detection and classification step and speed up processing.

Localization and object detection

Image localization is used to determine where objects are located in an image. Once identified, objects are marked with a bounding box. Object detection extends on this and classifies the objects that are identified. This process is based on CNNs such as AlexNet, Fast RCNN, and Faster RCNN.

Localization and object detection can be used to identify multiple objects in complex scenes. This can then be applied to functionalities such as interpreting diagnostic images in medicine. 

Semantic segmentation

Semantic segmentation, also known as object segmentation, is similar to object detection except it is based on the specific pixels related to an object. This enables image objects to be more carefully defined and does not require bounding boxes. Semantic segmentation is often performed using fully convolutional networks (FCN) or U-Nets. 

One popular use for semantic segmentation is for training autonomous vehicles. With this method, researchers can use images of streets or throughways with accurately defined boundaries for objects. 

Pose estimation

Pose estimation is a method that is used to determine where joints are in a picture of a person or an object and what the placement of those joints indicates. It can be used with both 2D and 3D images. The primary architecture used for pose estimation is PoseNet, which is based on CNNs. 

Pose estimation is used to determine where parts of the body may show up in an image and can be used to generate realistic stances or motion of human figures. Often, this functionality is used for augmented reality, mirroring movements with robotics, or gait analysis. 

Deep Learning for Computer Vision at Large Scale With Run:AI

Computer vision algorithms are highly compute-intensive, and may require multiple GPUs to run at production scale. Run:AI automates resource management and workload orchestration for machine learning infrastructure. With Run:AI, you can automatically run as many compute intensive experiments as needed. 

Here are some of the capabilities you gain when using Run:AI: 

  • Advanced visibility—create an efficient pipeline of resource sharing by pooling GPU compute resources.
  • No more bottlenecks—you can set up guaranteed quotas of GPU resources, to avoid bottlenecks and optimize billing.
  • A higher level of control—Run:AI enables you to dynamically change resource allocation, ensuring each job gets the resources it needs at any given time.

Run:AI simplifies machine learning infrastructure pipelines, helping data scientists accelerate their productivity and the quality of their deep learning models. 

Learn more about the Run.ai GPU virtualization platform.

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