1. rubyplot
  2. tutorial
  3. magick
  4. Image

Rubyplot Image Tutorial

This tutorial contains a tutorial for Rubyplot Image
P.S. - Currently only for Magick backend

Table of Contents

  1. Copying an image
  2. Copying a part of an image
  3. Changing channels
    3a. Exporting specific order of maps
    3b. Importing specific order of maps
  4. Adding padding
  5. Manipulating Values (using Numo array)
In [1]:
require 'rubyplot' # Import rubyplot
Rubyplot.inline # Setting inline plotting

1. Copying an Image

Following steps are taken:

  1. The image is read and stored in a Rubyplot::Image object
  2. Pixels are exported from the image
  3. A new Rubyplot::Image object is created with specified rows and columns
  4. Exported pixels are imported to the Rubyplot::Image object
In [2]:
img0 = Rubyplot::Image.new # Creating a new Image Object
img0.imread('mnist0.jpg') # Reading a MNIST Image
img0.imshow # Showing the Image
Out[2]:
In [3]:
img0_pix = img0.export_pixels("I") # Exporting pixels from img0, map is set as intensity(I) as the image is grayscale
img0_copy = Rubyplot::Image.new(img0.columns,img0.rows) # Creating an Image to copy img0 with same number of columns and rows
img0_copy.import_pixels(img0_pix,"I") # Importing pixels extracted from img0
img0_copy.imshow # Showing the copied image
# img0_copy.imwrite("mnist0_copy.jpg") # Image can be written with any format
Out[3]:

2. Copying a part of an image

Following steps are taken:

  1. The image is read and stored in a Rubyplot::Image object
  2. Pixels are extracted from the image with an offset and specified dimensions
  3. A new Rubyplot::Image object is created with specified rows and columns equal to exported dimensions
  4. Extracted pixels are imported to the Rubyplot::Image object
In [4]:
img1 = Rubyplot::Image.new # Creating a new Image Object
img1.imread('cat.jpg') # Reading an image of a cat
img1.imshow # Showing the Image
Out[4]:
In [5]:
# Columns and Rows in Image
puts('Columns in image = '+img1.columns.to_s)
puts('Rows in image = '+img1.rows.to_s)

Columns in image = 1920
Rows in image = 840
In [6]:
img1_pix = img1.export_pixels("RGB",900,50,800,750) # Exporting pixels from img1, map is set as RGB as the image is RGB
# 800x750 pixels are exported from the position (900,50) i.e. offset is (900,50)
img1_copy = Rubyplot::Image.new(800,750) # Creating an Image to copy img1 with number of columns and rows exported
img1_copy.import_pixels(img1_pix) # Importing pixels extracted from img1
img1_copy.imshow # Showing the copied image
# img1_copy.imwrite("cat_copy.jpg") # Image can be written with any format
Out[6]:

3. Changing channels

This can be done in two ways:

In [7]:
img2 = Rubyplot::Image.new # Creating a new Image Object
img2.imread('rgb.png') # Reading an image
img2.imshow # Showing the Image
Out[7]:

3a. Exporting specific order of maps

Following steps are taken:

  1. The image is read and stored in a Rubyplot::Image object
  2. Pixels are exported from the image in the order BRG
  3. A new Rubyplot::Image object is created with specified rows and columns
  4. Exported pixels are imported to the Rubyplot::Image object in the order RGB

Since RGB is exported in order BRG; Blue becomes Red, Red Becomes Green and Green becomes Blue i.e. BRG -> RGB

In [8]:
img2_pix_brg = img2.export_pixels("BRG") # Exporting pixels from ima2, map is set as BRG
img2_copy_brg = Rubyplot::Image.new(img2.columns,img2.rows) # Creating an Image to copy img2 with same number of columns and rows
img2_copy_brg.import_pixels(img2_pix_brg,"RGB") # Importing pixels extracted from img2 in the order RGB
img2_copy_brg.imshow # Showing the copied image
# img2_copy_brg.imwrite("brg.png") # Image can be written with any format
Out[8]:

3b. Importing specific order of maps

Following steps are taken:

  1. The image is read and stored in a Rubyplot::Image object
  2. Pixels are exported from the image in the order RGB
  3. A new Rubyplot::Image object is created with specified rows and columns
  4. Exported pixels are imported to the Rubyplot::Image object in the order GBR

Since RGB is imported in order GBR; Red becomes Green, Green Becomes Blue and Blue becomes Red i.e. RGB -> GBR

In [9]:
img2_pix_gbr = img2.export_pixels # Exporting pixels from img2, map is set as RGB as the image is RGB
img2_copy_gbr = Rubyplot::Image.new(img2.columns,img2.rows) # Creating an Image to copy img2 with same number of columns and rows
img2_copy_gbr.import_pixels(img2_pix_gbr, "GBR") # Importing pixels extracted from img2 in the order GBR
img2_copy_gbr.imshow # Showing the copied image
# img2_copy_gbr.imwrite("gbr.png") # Image can be written with any format
Out[9]:

4. Adding padding

In [10]:
img3 = Rubyplot::Image.new # Creating a new Image Object
img3.imread('cat2.jpeg') # Reading an image of a cat
img3.imshow # Showing the Image
Out[10]:
In [11]:
# Columns and Rows in Image
puts('Columns in image = '+img3.columns.to_s)
puts('Rows in image = '+img3.rows.to_s)

Columns in image = 252
Rows in image = 200
In [12]:
img3_pix = img3.export_pixels # Exporting pixels from img3, map is set as default(=RGB) as the image is RGB
img3_copy = Rubyplot::Image.new(500,500) # Creating an Image to copy img1 with more number of columns and rows than exported
img3_copy.import_pixels(img3_pix,"RGB",120,150,252,200) # Importing pixels extracted from img3 to offset (120,150)
img3_copy.imshow # Showing the copied image
# img3_copy.imwrite("cat2_copy.jpg") # Image can be written with any format
Out[12]:
In [13]:
# Columns and Rows in Image
puts('Columns in image = '+img3_copy.columns.to_s)
puts('Rows in image = '+img3_copy.rows.to_s)

Columns in image = 500
Rows in image = 500

5. Manipulating Values (using Numo array)

In [14]:
img4 = Rubyplot::Image.new # Creating a new Image Object
img4.imread('paris.jpeg') # Reading an image
img4.imshow # Showing the Image
Out[14]:
In [15]:
# Columns and Rows in Image
puts('Columns in image = '+img4.columns.to_s)
puts('Rows in image = '+img4.rows.to_s)

Columns in image = 500
Rows in image = 747
In [16]:
require 'numo/narray'
img4_pix = img4.export_pixels # Exporting pixels from img4, map is set as RGB as the image is RGB
img4_pix_narray = Numo::DFloat.cast(img4_pix) # Casting exported pixel array as a Numo::DFloat array
puts('Converted Ruby Array to Numo array of shape '+img4_pix_narray.shape.to_s)

Converted Ruby Array to Numo array of shape [3, 747, 500]
In [17]:
# Manipulating Numo array
img4_pix_narray_new = Numo::DFloat.cast(img4_pix_narray>(Rubyplot.QuantumRange/3)) * Rubyplot.QuantumRange
puts 'Choosing pixels which have more intensity than Rubyplot.QuantumRange/3 for each channel'
# Intensity of a pixel ranges from 0 to Rubyplot.QuantumRange

Choosing pixels which have more intensity than Rubyplot.QuantumRange/3 for each channel
In [18]:
img4_copy = Rubyplot::Image.new(img4.columns,img4.rows) # Creating an Image to copy img4 with number of columns and rows exported
img4_copy.import_pixels(img4_pix_narray_new) # Importing pixels extracted from img4
img4_copy.imshow # Showing the copied image
# img4_copy.imwrite("paris_copy.jpg") # Image can be written with any format
Out[18]:
In [ ]: