CNNs and Feature Selection
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Questions and Answers

What is the primary advantage of using Convolutional Neural Networks (CNNs) in computer vision?

  • They are not suitable for image data.
  • They automatically learn relevant features from the data. (correct)
  • They require manual feature extraction.
  • They require more computational power.

What is the purpose of the convolution operation in a CNN?

  • To increase the number of channels in the input image.
  • To perform element-wise multiplication with the input.
  • To extract features from the input using a filter. (correct)
  • To reduce the dimensions of the input image.

What is the role of a 'filter' in the convolution operation?

  • To add noise to the image.
  • To blur the image.
  • To detect specific features or patterns in the input. (correct)
  • To increase the resolution of the image.

Which of the following is a common operation performed after a convolution layer in a CNN?

<p>Pooling (A)</p> Signup and view all the answers

What is the role of the ReLU (Rectified Linear Unit) activation function in CNNs?

<p>To introduce non-linearity into the network. (C)</p> Signup and view all the answers

What is 'pooling' in the context of Convolutional Neural Networks?

<p>A method to reduce the spatial size of the feature map. (C)</p> Signup and view all the answers

What is the purpose of the 'flatten' operation in a CNN?

<p>To convert multi-dimensional data into a one-dimensional vector. (D)</p> Signup and view all the answers

How do fully connected layers contribute to the functionality of a CNN?

<p>By connecting every neuron from the previous layer to every neuron in the current. (C)</p> Signup and view all the answers

What does the term 'stride' refer to in the context of convolutional layers?

<p>The step size the filter moves across the input. (A)</p> Signup and view all the answers

What is 'padding' used for in CNNs?

<p>Preserving the spatial size of the input after convolution. (A)</p> Signup and view all the answers

Which of the following is typically reduced through the use of pooling layers?

<p>Spatial resolution (D)</p> Signup and view all the answers

What is a potential drawback of using very large fully connected layers in CNNs?

<p>Higher risk of overfitting and increased computational cost. (A)</p> Signup and view all the answers

In the context of CNNs, what is 'parameter sharing'?

<p>Using the same filter across different locations in the input. (B)</p> Signup and view all the answers

How does parameter sharing contribute to the effectiveness of CNNs?

<p>It reduces the number of trainable parameters. (D)</p> Signup and view all the answers

What is the purpose of flattening the output of the convolutional layers before feeding it into a fully connected layer?

<p>To convert the 2D feature maps into a 1D feature vector. (A)</p> Signup and view all the answers

What characteristic is enhanced by using CNNs rather than ANNs for image processing?

<p>The need for manual feature extraction diminishes. (A)</p> Signup and view all the answers

What is the primary reason that fully connected neural networks are not typically used for large, high-resolution images?

<p>The number of weights becomes impractical. (B)</p> Signup and view all the answers

If a CNN has an input layer of size 5x5, a kernel of size 3x3, and a stride of 1 with no padding, what will be the size of the output feature map?

<p>3x3 (A)</p> Signup and view all the answers

A CNN has a 6x6 input, uses a 3x3 filter, a stride of 2, and no padding. What is the dimension of the resulting feature map?

<p>2x2 (D)</p> Signup and view all the answers

In a CNN, if a layer has a 10x10 input, a 5x5 kernel, a stride of 1, and padding of 2, what is the size of the output feature map?

<p>10x10 (A)</p> Signup and view all the answers

What is the primary benefit of using 1x1 convolutions in CNNs?

<p>They reduce the number of channels. (C)</p> Signup and view all the answers

Consider a grayscale input image being processed by a CNN. If a convolutional layer has a 3x3 kernel, how many parameters are associated only with the kernel itself (ignoring biases)?

<p>9 (C)</p> Signup and view all the answers

Consider a CNN layer with a 3x3 kernel processing a grayscale image. If the layer's output is 4 feature maps, what is the total number of parameters used by the kernels and biases in this layer?

<p>40 (B)</p> Signup and view all the answers

In the context of image processing with CNNs, what does the term 'pixel depth' typically refer to?

<p>The number of bits used to represent each color channel. (C)</p> Signup and view all the answers

What characterizes a 'dilated convolution' compared to a standard convolution?

<p>It introduces gaps within the kernel. (C)</p> Signup and view all the answers

Which of the following is a typical application of CNNs involving pixel-level classification?

<p>Semantic segmentation (A)</p> Signup and view all the answers

Which of the following is a computer vision application that benefits significantly from CNNs?

<p>Medical image analysis (C)</p> Signup and view all the answers

What is the purpose of 'transfer learning' in the context of CNNs?

<p>To apply knowledge gained from solving one problem to a different but related problem. (B)</p> Signup and view all the answers

Which of the following is an example of an application of CNNs in recycling technology?

<p>Sorting waste based on chemical properties (C)</p> Signup and view all the answers

What type of data is typically fed into a CNN designed to classify plastic types based on infrared spectra?

<p>One-dimensional array of spectrum intensity. (A)</p> Signup and view all the answers

What type of layers are typically included in the architecture of a CNN designed for plastic classification?

<p>Convolutional 1D, Maxpool 1D. (D)</p> Signup and view all the answers

During the use of a CNN for plastic identification based on infrared spectrum analysis, what is represented by the 'filter size'?

<p>The dimensions of the convolutional kernel. (C)</p> Signup and view all the answers

During the use of a CNN for plastic identification based on infrared spectrum analysis, what is represented by the 'number of filters'?

<p>The individual characteristics of the model. (C)</p> Signup and view all the answers

What does the term 'activation' refer to in the context of CNNs designed for plastic classification?

<p>Non-linear functions to model complex dependencies. (B)</p> Signup and view all the answers

What does the stride parameter in a convolutional layer control?

<p>Controls the movement of the filter across the full image. (C)</p> Signup and view all the answers

What is the purpose of 'instancing segmentation' in CNNs?

<p>To sort individual objects. (A)</p> Signup and view all the answers

What is one of the key considerations for using CNNs in real-time applications, such as autonomous driving?

<p>Model size and computational efficiency (C)</p> Signup and view all the answers

In a CNN, if a layer's configuration requires calculating $n^{(l)} = \lfloor \frac{n^{(l-1)} + 2p^{(l-1)} - f^{(l)}}{s^{(l)}} + 1 \rfloor$, and $n^{(l-1)} = 7$, $p^{(l-1)} = 1$, $f^{(l)} = 3$, and $s^{(l)} = 2$, what is the value of $n^{(l)}$?

<p>4 (B)</p> Signup and view all the answers

When calculating the number of weights in a convolutional layer, what factors directly influence the total count?

<p>Kernel size, the quantity, channels and activations. (C)</p> Signup and view all the answers

What is the main reason for using a softmax activation function in the final layer of a CNN designed for image classification?

<p>To produce a probability distribution over classes. (C)</p> Signup and view all the answers

What is the result of representing each color in an image with one byte?

<p>A possible 256 color values. (B)</p> Signup and view all the answers

How does the use of a 2D convolution differ from using a 1D convolution?

<p>2D convolutions can process spatial relationships in images or matrices. (D)</p> Signup and view all the answers

In image processing, what is the primary function of convolution?

<p>To enhance certain features within the image. (C)</p> Signup and view all the answers

What is the impact of increasing the stride in a convolutional layer?

<p>It reduces the spatial dimensions of the output. (C)</p> Signup and view all the answers

What effect does padding have on the output size of a convolutional layer?

<p>Padding helps in retaining the original input size or managing the reduction in size. (D)</p> Signup and view all the answers

What is the main purpose of using pooling layers in a CNN?

<p>To reduce spatial resolution and computational complexity. (C)</p> Signup and view all the answers

In a convolutional layer, what does the term 'weights' refer to?

<p>The parameters within the convolutional filter/kernel. (C)</p> Signup and view all the answers

What is the advantage of using CNNs over fully connected ANNs when processing images?

<p>CNNs automatically learn spatial hierarchies of features. (B)</p> Signup and view all the answers

What is the primary reason for the impracticality of using fully connected layers for very large images?

<p>The number of parameters becomes exceedingly large. (D)</p> Signup and view all the answers

Given a CNN layer configuration where $n^{(l-1)} = 9$, $p^{(l-1)} = 2$, $f^{(l)} = 5$, and $s^{(l)} = 2$, what is the output size $n^{(l)}$ using the formula $n^{(l)} = \lfloor rac{n^{(l-1)} + 2p^{(l-1)} - f^{(l)}}{s^{(l)}} + 1 floor$?

<p>5 (B)</p> Signup and view all the answers

Which factors directly affect the number of weights in a convolutional layer?

<p>The number of filters, kernel size, and depth of the input volume. (D)</p> Signup and view all the answers

What is the purpose of the softmax activation function in the final layer of a CNN image classifier?

<p>To normalize the output into a probability distribution across classes. (C)</p> Signup and view all the answers

What kind of data is suitable for input into a CNN intended for classifying varying types of plastics using infrared spectra?

<p>Numerical data representing infrared spectrum readings. (B)</p> Signup and view all the answers

How does increasing the kernel size in a convolutional layer affect the feature extraction process?

<p>It increases the receptive field, capturing more contextual information.. (D)</p> Signup and view all the answers

How would using dilated convolution, instead of traditional convolution, specifically influence feature extraction?

<p>Dilated convolution enables a larger receptive field without increasing parameters. (B)</p> Signup and view all the answers

What distinguishes 'semantic segmentation' from other CNN applications?

<p>In the semantic segmentation, each pixel in the input image is classified. (D)</p> Signup and view all the answers

In the context of CNNs, what is the primary benefit of transfer learning?

<p>It speeds up training and improves performance with less data. (C)</p> Signup and view all the answers

How does parameter sharing contribute to the efficiency of CNNs in image processing tasks?

<p>It significantly reduces the number of trainable parameters. (A)</p> Signup and view all the answers

What is the primary difference between using CNNs and ANNs for large, high-resolution images?

<p>CNNs automatically learn spatial hierarchies of features, while ANNs do not. (A)</p> Signup and view all the answers

How can CNNs contribute to recycling technology?

<p>By analyzing infrared spectra to classify different types of plastics. (B)</p> Signup and view all the answers

Why would you choose to use 1x1 convolutions in a CNN?

<p>To reduce or increase the number of feature maps. (A)</p> Signup and view all the answers

What is the significance of 'pixel depth' when representing images in CNNs?

<p>The number of bits used to represent each color channel. (D)</p> Signup and view all the answers

In a CNN designed for plastic identification using infrared spectrum analysis, what does the 'number of filters' typically represent?

<p>The number of distinct spectral features the network can learn. (C)</p> Signup and view all the answers

What does the term 'activation' refer to in CNNs designed for classifying plastic types?

<p>The output of a neuron after processing its inputs. (C)</p> Signup and view all the answers

What role does 'instancing segmentation' play in CNN applications for autonomous driving?

<p>Distinguishing and categorizing each individual object in the vehicle's environment. (A)</p> Signup and view all the answers

Flashcards

What are CNNs?

CNNs are a type of artificial neural network that are widely used in computer vision tasks.

How are images represented?

Images are represented as 2-dimensional arrays of pixel values.

What are RGB values?

Represents amount of Red, Green and Blue.

What are Convolutions?

The process of using feature detectors (filters) to extract relevant information from input images.

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What is a convolutional filter?

The filter is a set of weights used in the convolution operation.

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What is Stride?

The number of pixels by which the filter shifts during convolution.

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What is Padding?

Adding extra layers of 'fake' pixels around the images to avoid shrinking

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What is Pooling?

A technique to reduce the spatial size of the representation, reducing the number of parameters and computation in the network.

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What is a Fully Connected Layer?

A layer in a neural network that connects every neuron in one layer to every neuron in the next layer.

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What is Flattening?

Converts the output of the convolutional layers into a 1D feature vector for the fully connected layer.

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What is Machine Learning?

A process of teaching models to perform specific tasks without being explicitly programmed.

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What is the color depth?

Each color (RGB) is represented by a byte. 256 possible values for colour depth.

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What are Dilated Convolutions?

A type of convolution where the filter is applied with gaps between the pixels. Increases receptive field.

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Study Notes

  • CNNs are predominant in Computer Vision (CV) for feature learning and classification.
  • An image can be represented as a 2-dimensional array.
  • A buffer is moved to video memory enabling the display of the image.
  • Pixel values are stored as arrays.
  • RGB Values are used for color displays.
  • One byte represents a typical color so there are 256 possible values, representing pixel depth.
  • Using ANNs means every single pixel is connected to a node.
  • Full HD images can be 1920 * 1080 * 3 = 6,220,800.
  • Connecting to a layer of 1,024 would require 6,370,100,224 weights, this is impractical in space in time.

Feature Selection

  • Feature selection is used to process images more efficiently than ANNs.
  • Likewise for 2D vectors, matrices, and images

Convolutions

  • Convolutions apply a filter matrix to the original image to process it.
  • Automated feature extraction is possible through Machine and deep learning.
  • In Machine learning: Input -> Feature extraction -> classification - > Output.
  • In Deep Learning Input - > Feature extraction & classification - > Output.

Convolution Parameters

  • Input is fed into the filter to retrieve a result.
  • Size: f = 3.
  • Stride: s = 1.
  • Padding: p = 0.
  • Weights are calculated: 3 x 3 kernel, 1 input; Output: (3x3) + 1 bias; total = 10.
  • 2D Convolutions use a sliding window and are expressed in vector form
  • The output is expressed as y = h * x

Convolution Calculations

  • nl = (n(l-1) + 2p(l-1) - f(l) / s(l)) + 1 where:

    • l = layer.
    • p = padding.
    • f = kernel size.
    • s = stride.
  • Dilated convolutions can be used

Pooling Layer

  • Max pooling and average pooling reduce the size of the matrix to focus on the most important parts.

Convolutional Layers

  • Convolutional layers use size, stride, and padding to reduce the size of the information for increased performance.

  • The number of channels is also a consideration in the outcome, and different outputs can be achieved through different numbers of channels.

  • Calculation of parameters, 3 x 3 kernel; grey scale Input; output 4:

    • (3 x 3 (kernel) x 4 (output) = 36).
    • bias = 4.
    • total = 40.
  • Likewise for calculating parameters, 3 x 3 kernel; RGB Input; output 8:

    • (3 x 3) (kernel) x 3(depth RGB) x 8 (output) = 216.
    • Bias = 8.
    • Total: 224.

Image Processing

  • 1x1 convolutions can be used to achieve similar effects as regular convolutional layers.

Flattening

  • Flattening is used as an input to a fully connected network.
  • Classifying a digit: Input 32x32, C1 feature maps 6@28x28, S2 maps 6@14x14, C3 maps 16@10x10, S4 maps 16@5x5, C5 layer 120, F6 Layer 84, output 10.

CNN Benefits

  • CNNs take inspiration from deep learning to quantify image information like the beauty of outdoor places.
  • CNNs share parameters to save on time and space.
  • CNNs use automated feature extraction.
  • They are practical method for many applications.

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Explore Convolutional Neural Networks (CNNs) in computer vision for feature learning and classification. Learn how CNNs process images more efficiently than ANNs using feature selection and convolutions. Understand the impracticality of connecting every pixel to a node due to the high number of weights required.

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