Rubyplot Image Tutorial¶

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

Table of Contents¶

Copying an image
Copying a part of an image
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:

The image is read and stored in a Rubyplot::Image object
Pixels are exported from the image
A new Rubyplot::Image object is created with specified rows and columns
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:

The image is read and stored in a Rubyplot::Image object
Pixels are extracted from the image with an offset and specified dimensions
A new Rubyplot::Image object is created with specified rows and columns equal to exported dimensions
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:

The image is read and stored in a Rubyplot::Image object
Pixels are exported from the image in the order BRG
A new Rubyplot::Image object is created with specified rows and columns
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:

The image is read and stored in a Rubyplot::Image object
Pixels are exported from the image in the order RGB
A new Rubyplot::Image object is created with specified rows and columns
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]:

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