1. Introduction

Modern face recognition pipelines consist of 4 common stages

  • Detection
  • Alignment
  • Representation
  • Verification

2. Detection and alignment

Detection

  • OpenCV offers haar cascade and Single Shot Multibox (SSD)
  • Dlib offers Histogram of Oriented Gradient(HOG) and CNN based Max-Margin Object Detection (MMOD) and Multi-task Cascaded Convolutional Network (MTCNN)

Alignment

  • Alignment is easy if face and eyes detected already
  • But neither openCV nor dlib offer face alignment as an out-of-box function
  • We have to do some trigonometry here to align faces

Retinaface is the cutting-edge face detection technology.

  • It can even detect faces in the crowd and it finds facial landmarks including eye coordinates

Deepface offer both face detection and face alignment as a function. It wraps openCV’s haar cascade, SSD, dlib HoG, MTCNN and retinaface. It also does some math and trigonometry to align faces. Deepface use default configuration OpenCV’s haar cascade. `shell import numpy as np from deepface import DeepFace from deepface.commons import functions

model_name = “VGG-Face”

target_size = functions.functions(model_name = model_name)

img1 = DeepFace.extract_faces(img_path = “img1.jpg”, target_size=target_size, detector_backend =”mtcnn”) img2 = DeepFace.extract_faces(img_path = “img2.jpg”, target_size=target_size, detector_backend = “mtcnn”)

img1 = np.expand_dims(img1, axis=0) #(224, 224, 3) to (1, 224, 224, 3) img2 = np.expand_dims(img2, axis=0) #(224, 224, 3) to (1, 224, 224, 3) `

3. Normalization

Face detector detect faces in a squared area. So, detected faces come with some noise such as background color. Dlib can find 68 facial landmarks.

  • We can extract face and get rid of any noise in this way.
  • This optional step is called as normalization in facial recognition. MediaPipe can find 468 landmarks https://sefiks.com/2022/01/14/deep-face-detection-with-mediapipe/ https://sefiks.com/2022/01/15/virtual-background-with-mediapipe/

4. Representation

  • Deep learning just appears in this representation stage.
  • We will feed face images to a CNN model but the task is here is not classification.
  • We will use CNN models to find embeddings similar to autoencoders.
  • The most popular face recognition models are VGG-Face, Google FaceNet, OpenFace and Facebook DeepFace. shell model_name = "VGG-Face" model = DeepFace.build_model(model_name = model_name)
  • These models have different input and output shapes.
    • VGG-Face (224, 224, 3) -> 2622 dimensional vector
    • FaceNet (160, 160, 3) -> 128 dimensional vector
  • We have to pass the input shape to detectFace function in the detet and align stage.
  • We must put detectFace command after input shape retrieved.
Figure 2. Sample open-source software for IBM Z and LinuxONE. Image source: [IBM community].

2. Why use Linux?

  • - Open source
    • - Linux is an open source operating system
    • - Anyone, whether an individual or a corporation, can install and use Linux for free.
    • - open source movement
  • - Customizing
    • - Linux strictly means the Linux kernel.
      • - The kernel is a part of the OS that performs the core functions of the OS.
    • - Only the core functions that Linux OS needs to perform are defined, and the other parts can be customized and used by the user according to his/her own use.
  • - Stable operation
    • - Since it is open source, various users can verify it in real time.
Figure 3. Linux-command. Image source: [joffi from Pixabay].

3. Linux(UNIX) Required Commands

3.1. CLI(Command Line Interface) commands

  • - Made for i18n (internationalization)
  • - UTF-8 is used as the default character set
  • - It is recommended to use the en_US locale as it is affected by the setting of the LANG environment variable

3.1.1. File

  • - Path
    • - command
      • pwd: print working directory
      • cd: change directory
    • /: root directory
    • ~: home directory
    • -: previous directory
    • - Path type
      • - Absolute path (abs-path): path starting from the root directory
      • - Relative path: path starting from the current directory (.)
  • - Check
    • - command
      • - ls, file, stat, which, find
    • - file mode bit: 3+9 bit system representing UNIX file permissions
      • - how to write
        • - Symbolic mode:
          • How to mark with rwx symbol
          • Consists of owner, group, and others parts, each with 3 spaces
          • -r: readable, -w: writable, -e: executable
        • - Octal mode: A method of expressing bits in octal notation
    • - stat: outputs status of file, meta data of file
      • - meta data: Modifying information, not content (file name, creation time, permissions)

    • - touch: update meta data of file, create an empty file if file does not exist

    • - find: find directory
      • -name filename: search for files with the same name as filename
      • -size n: search for files of size n
      • -mtime n: search for files with modified time n
      • -inum n: Search for files with inode number n
      • -max(min)depth level: Search for files with a maximum (minimum) depth of level in the subdirectory of the location to be searched
      • $ex1.$ find . -name '*k.data' -a -size 1M (-a: AND, -o: OR)
      • $ex2.$ find -name "*.tmp" -exec rm {}\;
        • - *.tmpfiles are put in {}
        • - The meaning of \ is that the command is executed while searching one by one.
        • - \+ finds everything and executes the command at once
      • practice 1. Find general files whose contents have been changed within the last 24 hours under the current directory and save the list as mtime_b24.txt file
        • find ./ -mtime -1 -type f > mtime_b24.txt
      • practice 2. If it goes beyond the 3rd level under the current directory, it is not searched, and all files that satisfy the condition are copied to the ~/backup directory.
        • find ./ -maxdepth 3 ... -exec cp {} ~/backup \;
Figure 4. File descriptor.
  • - stdio (standard input/output)
    • File channel: channel for input/output to file
      • - A kind of virtualization layer that allows standardized input/output methods to be used to input/output channels to files without being directly transferred to hardware.
      • - file channel: object with meta information for input/output to a file
      • - Enables simplicity of I/O interface in C language
    • File descriptor (often used as file descriptor, fd)
      • - Unique idenfifier attached to file channels, named numerically
      • - Starting from positive number 0 and increasing
      • - Reserved file descriptors: 0 (stdin), 1 (stdout), 2 (stderr)
      • - The fd value is given within the process. Can’t I open the same file twice?
        • - Even if the same process opens the same file, a new pd value is assigned. It’s possible, but there’s a possibility of overlapping updates.

      • used as communication between PIPE processes

      • - A type of IPC (inter-process communication)
        • Anonymous pipe
          • serial connection of processes (A|B|C)
          • Temporarily created and destroyed pipes
          • Created by using | (vertical bar) in the shell.
          • $ex$. find ~ | wc -l
            • find ~: find all files under the home directory
            • | Since there is a pipe, since it is wc (word count), it is per line, so I want to know how many files are under the home directory.
            • The output of the find command (stdout) is concatenated with the input (stdin) of the wc command.
            • Has the same meaning as find ~ > tmp.txt; wc -l < temp.txt; rm tmp.txt.
            • fd: 1 is connected to fd: 0 via a pipe
            • When using the wc -l option, the number of lines is counted.
        • Named pipes
          • In Unix, the implementation of a named pipe is called a FIFO pipe.
          • It is structured like a file, so there is a path+filename.
          • Expresses that having a path is named.
          • mkfifo or POSIX C API
    • Redirection
      • Link the direction of a channel to another place
      • A > B : connect (save) A’s stdout to file B
        • ex. ls -a > ls.txt
      • A < B : link A’s stdin to file B
      • A >> B: direction is the same as “>”, append mode
        • ex. strace ls 2> strace.txt
          • 2> means a command that connects file descriptor number 2 to a file.
          • Save the output of stderr, which is fd 2, to a file.
    • cat: default filter to freely link stdout to files
      • Used to output the contents of a file to stdout
      • Used to redirect input from stdin and output it to a file
      • $ex$. cat ~/.bashrc
      • $ex$. cat > hello.txt Then, if you write Hello world and do ^D, Hello world is entered into hello.txt and exited.
  • - Change data
    • - command
      • - cp, mv, rm, mkdir/rmdir, ln
      • - mkdir: make directory
      • - rmdir: remove directory (In many cases, files and directories are deleted together with rm -rf instead of rmdir.)
      • - cp: copy
      • - mv: move, rename
      • - rm: remove
  • - Meta change
    • - command
      • - chmod: change mode
      • - chown, chgrp: change owner/group
  • - Archive
    • - tar
      • An archive is a grouping of multiple files.
      • tar -ctxv
        • -c (create): create an archive
        • -t(test) : test the archive
        • -x (extract) : Extracts a file from an archive
        • -v (verbose): output detailed information (not used in practice)
        • f archive-file: Archive file name to input/output --exclude file: Exclude the file from the target
      • $ex$. tar c *.c > arc_c.tar == tar cf arc_c.tar *.c (just give the f option. *.c files go into arc_c.tar)
  • - Compress
    • - gzip, zstd
      • The compression rate is xz > bzip2 > zstd > gzip > lz4
      • xz: Compression rate is good, but slow.
      • zstd: used a lot these days $ex$. The classic way to use tar and gzip together
      • compression: tar c /etc/*.conf | gzip -c > etc.tar.gz
      • release: gzip -cd etc.tar.gz | tar x

3.1.2. Text

  • - Editor
    • - vim(vi)
  • - Filter
    • - cat(tac), head, tail, less/more, sort
  • - Regex
    • - grep, sed, awk

3.1.3. Job control

  • - jobs, fg, bg

3.1.4. Process control

  • - kill, pkill, pgrep, strace(tracing)

3.1.5. Networking

  • - nc (net cat), curl, wget

3.1.6. Disk

  • - df

3.1.7. System

  • - free, top, ps, pidstat, lshw

3.2. Admin commands

3.2.1. Package

  • - Redhat: rpm, yum
  • - Debian: dpkg, apt

3.2.2. Network

  • - status: ss, netstat(old fashion)
  • - config: nmcli, ip
  • - ssh
  • - packet: tcpdump, wireshark, tshark

3.2.3. Files and kernel

  • - lsof
  • - sysctl

3.2.4. Disks

  • - fdisk, parted, mkfs, mount, lsblk, blkid, grubby, udisksctl

3.2.5. User

  • - useradd, groupadd, usermod
  • - passwd, chpasswd