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Questions and Answers

What problem do Residual Networks primarily aim to address?

  • Overfitting caused by shallow networks.
  • The difficulty in propagating gradients through deep networks. (correct)
  • Decreased computational efficiency in CNNs.
  • The increase in model complexity without performance gain.
  • What is a primary benefit of edge detectors in relation to the input pixels?

  • They minimize the connection density between layers. (correct)
  • They provide a balanced representation of input data.
  • They summarize information from many input pixels.
  • They prevent noise from affecting performance.
  • What is a key feature of Residual Networks that aids in gradient propagation?

  • Modification of the loss function.
  • Increased pooling layers between each layer.
  • Addition of skip connections. (correct)
  • Reduction in the number of layers.
  • What is a drawback associated with Residual Networks regarding output size?

    <p>Output size remains constant, limiting flexibility.</p> Signup and view all the answers

    What is the primary trade-off associated with the efficiency of Convolutional Neural Networks?

    <p>High computational cost for reduced parameters.</p> Signup and view all the answers

    What is one major advantage of using a 1 x 1 convolution layer?

    <p>It provides a nearly 10 times reduction in computational cost.</p> Signup and view all the answers

    What is the primary function of the encoder in an autoencoder?

    <p>To summarize input into embeddings.</p> Signup and view all the answers

    Which of the following best describes the purpose of data augmentation?

    <p>To improve model generalization in real-life scenarios.</p> Signup and view all the answers

    What type of autoencoder is specifically designed to remove noise from images?

    <p>Denoising autoencoder.</p> Signup and view all the answers

    Which of the following statements about depthwise separable convolutions is true?

    <p>They use fewer parameters than normal convolutions.</p> Signup and view all the answers

    What happens to the number of output channels when more filters are used in a convolutional layer?

    <p>The number of output channels increases.</p> Signup and view all the answers

    What is a key characteristic of pooling layers in CNNs?

    <p>They reduce the size of input without learning parameters.</p> Signup and view all the answers

    For a convolution kernel of size (3,3) with 10 filters operating on RGB images, how is the number of parameters calculated?

    <p>Kernel size multiplied by number of filters plus bias.</p> Signup and view all the answers

    What is a recommended size for convolution kernels in typical CNN structures?

    <p>3, 5 or 7</p> Signup and view all the answers

    What occurs to the height and width of the input as more convolutional layers are added?

    <p>They reduce while the number of channels increases.</p> Signup and view all the answers

    What is a primary advantage of using CNNs for image processing related to translational invariance?

    <p>They detect features regardless of their location.</p> Signup and view all the answers

    What is the function of flattening and dense layers at the end of a CNN?

    <p>To assist in downstream classification or regression tasks.</p> Signup and view all the answers

    What is the role of the stride in a convolutional layer?

    <p>It defines how much the kernel moves over the input.</p> Signup and view all the answers

    What is one significant advantage of using Convolutional Neural Networks (CNNs) over Dense networks when processing image data?

    <p>CNNs reduce the number of parameters, minimizing the chance of overfitting.</p> Signup and view all the answers

    What is the primary purpose of padding in convolution operations?

    <p>To prevent information loss at the borders of the image.</p> Signup and view all the answers

    How do strided convolutions help improve the computational efficiency of CNNs?

    <p>They allow the kernel to skip certain positions, reducing computation.</p> Signup and view all the answers

    What key feature does the receptive field of a CNN denote?

    <p>The amount of previous image information a pixel can influence.</p> Signup and view all the answers

    What is the effect of using dilated convolutions in a CNN?

    <p>It increases the receptive field without losing resolution.</p> Signup and view all the answers

    Why were handcrafted convolutional kernels largely replaced by learned kernels in CNNs?

    <p>Learned kernels can adapt and optimize based on data characteristics.</p> Signup and view all the answers

    In convolution operations with channels, what does it mean for inputs to have multiple channels?

    <p>Images are composed of several color channels, like RGB.</p> Signup and view all the answers

    What does the 'valid' padding option do in convolution operations?

    <p>Does not add any padding, thus reducing the output size.</p> Signup and view all the answers

    Study Notes

    Motivations for CNNs

    • Traditional dense networks struggle with large image data; a single 64 x 64 RGB image contains 12,288 integers.
    • Using a dense layer with 128 neurons can lead to over 1.5 million parameters in the first layer, increasing the risk of overfitting.
    • Memory constraints on GPUs make training large models challenging.
    • CNNs offer a solution with significantly fewer parameters.

    Convolutional Kernels

    • Convolutional kernels, like edge detectors, emphasize features such as edges in an image.
    • Prior to CNNs, convolution kernels were manually crafted; CNNs allow networks to learn these kernels via gradient descent.

    Padding

    • Convolutions typically reduce output size; padding maintains input size by adding zeros.
    • "Valid" padding adds no zeros, while "Same" padding ensures output size matches input size.

    Strided Convolutions

    • Stride affects how the kernel moves, enabling faster downsampling, reducing overfitting, and improving computational efficiency.
    • Larger strides increase the receptive field, the amount of information a pixel holds from the original image.

    Dilated Convolutions

    • Introduces zeros within the kernel, increasing its receptive field without increasing the number of parameters.

    Convolutions with Channels

    • In CNNs, processing multi-channel images (e.g., RGB) involves producing single output channels from each filter.
    • Multiple filters increase output channels by concatenating results along the channel axis.

    Example of Parameters in a Conv Layer

    • A convolution kernel of size (3,3) applied to RGB images with 10 filters results in significantly fewer parameters than dense layers, typically under 1 million.

    Typical CNN Structure

    • Common kernel sizes are 3, 5, or 7; stride should be less than kernel size.
    • As layers increase, height and width typically decrease while the number of channels increases.
    • Flattening and Dense layers are included for classification or regression tasks.

    Pooling Layers

    • Pooling layers reduce input size without learning parameters; they apply operations such as max pooling or average pooling.
    • Pooling operates per channel, maintaining the number of channels.

    Why CNNs are Good for Images

    • CNNs exhibit translational invariance, detecting features regardless of location.
    • Connections are sparse, with each output pixel summarizing information from only a subset of inputs.

    Residual Networks (ResNets)

    • ResNets address challenges of deeper networks, including performance drops and vanishing gradients.
    • Skip connections help gradients propagate effectively, supporting deeper architectures.

    Computational Cost of CNNs

    • While CNNs reduce model parameters, they may incur higher computational costs due to numerous input and output filters.

    Computational Cost Mitigations

    • 1 x 1 Convolution layers drastically cut computational costs.
    • Depthwise separable convolutions also reduce computational load significantly.

    Data Augmentation

    • Enhances model generalization; techniques include random brightness, contrast, cropping, flipping, hue adjustments, and JPEG quality variations.

    Image Autoencoders

    • Autoencoders consist of an encoder that compresses data into embeddings and a decoder that reconstructs the original input.
    • Applications include data exploration, denoising by extracting non-noisy features, and facilitating semi-supervised learning via embeddings without labels.

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