Pratik kamble: Created page with "{| border=1 | '''Time''' | '''Narration''' |- | 00:01 | Welcome to the spoken tutorial on '''Image manipulation using arrays'''. |- | 00:07 |In this tutorial, you will lear..."

2019-06-03T10:00:18Z

Created page with "{| border=1 | '''Time''' | '''Narration''' |- | 00:01 | Welcome to the spoken tutorial on '''Image manipulation using arrays'''. |- | 00:07 |In this tutorial, you will lear..."

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{| border=1
| '''Time'''
| '''Narration'''

|-
| 00:01
| Welcome to the spoken tutorial on '''Image manipulation using arrays'''.

|-
| 00:07
|In this tutorial, you will learn to -

Read '''images''' into '''arrays'''

Perform processing on them using simple array manipulations

|-
| 00:19
|To record this tutorial, I am using

'''Ubuntu Linux 16.04''' operating system

'''Python 3.4.3 '''and

'''IPython 5.1.0'''

|-
| 00:35
| To practise this tutorial, you should know how to run basic '''Python commands''' on the '''ipython console '''and access parts of '''arrays'''.

|-
| 00:46
|If not, see the relevant '''Python '''tutorials on this website.

|-
| 00:51
| Please download the files''' Squares.png '''and '''Python.png''' from the '''Code files''' link of this tutorial.

|-
| 01:00
| Save the files in the current '''working directory'''.

|-
| 01:04
| First we will learn how to '''access''' parts of an '''array'''.

|-
| 01:09
| For this purpose, we shall use the image '''Squares.png''' present in the current '''working directory'''.

|-
| 01:16
| Let us start '''ipython'''. Open the '''terminal'''.

|-
| 01:21
| Type '''ipython3 '''and press '''Enter.'''

|-
| 01:26
| From here onwards remember to press the '''Enter''' key after typing every '''command''' on the '''terminal'''.

|-
| 01:33
| To read an '''image''' into an '''array''', we use the '''imread command'''.

|-
| 01:38
| Let us now read the data in '''Squares.png''' into the array '''img'''.

|-
| 01:44
| Type, '''import matplotlib.pyplot as plt'''

|-
| 01:51
| Then type, '''img''''' is equal to''''' plt.imread '''''inside brackets inside single quotes '''''Squares.png '''

|-
| 02:02
| In the first line '''pyplot''' is imported from '''matplotlib '''module with '''plt '''as alias.

|-
| 02:09
| This is to make use of '''methods''' like '''imread '''which are part of '''pyplot.'''

|-
| 02:15
| We can see the image by using the '''functions imshow''' followed by '''show'''.

|-
| 02:21
| Type, '''plt.imshow '''''inside brackets '''''img''' Then type, '''plt.show '''''open and close brackets''

|-
| 02:33
| It displays the image in a separate popup window.The original image is in the black and white.

|-
| 02:41
| But here we do not see black and white, because '''imshow''' has '''mapped''' black and white to different colors.

|-
| 02:49
| This can be changed by using a different '''color map'''.

|-
| 02:53
| Close the image window to return to the '''IPython console'''.

|-
| 02:58
| In order to see the original black and white image type, '''plt.imshow '''''inside brackets '''''img '''''comma''''' cmap '''''is equal to inside single quotes '''''gray'''

|-
| 03:13
| Then type, '''plt.show '''''open and close brackets''. Now we can see the image in black and white.

|-
| 03:22
| Close the image now.

|-
| 03:24
| To see what has been read into '''img''' variable, type,'''img'''. We can see that an '''array''' is displayed.

|-
| 03:34
| To check the '''dimensions''' of any '''array''', we can use '''shape function'''. Type, '''img.shape '''

|-
| 03:44
| As we can see, we got the dimensions of the image. The image''' Squares.png''' has the dimensions of 300 by 300.

|-
| 03:54
| Now, we wish to obtain the top left quarter of the image.

|-
| 03:59
| To do this, we need to access top half of the rows and left half of the columns of the '''array'''.

|-
| 04:06
| We know that the shape of the image is 300 by 300.

|-
| 04:11
| For '''top'''-'''left''' '''corner''' of the '''image '''we need first 150 '''rows''' and the first 150 '''columns'''.

|-
| 04:19
| So type, '''img '''''inside square brackets colon''''' 150 '''''comma colon''''' 150'''

|-
| 04:27
| This gives us the '''top'''-'''left''' '''corner''' of the '''image'''.

|-
| 04:32
| We use the '''imshow command''' to see the slice we obtained in the form of an image. Type as shown.

|-
| 04:42
| We got the required slice now. Close this image.

|-
| 04:48
| Pause the video. Try this exercise and then resume the video.

|-
| 04:54
| Obtain the square in the center of the image '''Squares.png''' with size 150 by 150.

|-
| 05:02
| Since we need to get center of the image, we take rows from one-fourth to three-fourth of the rows i.e. from '''75''' to '''225''' and columns from one-fourth to three-fourth of the columns, i.e. from '''75''' to '''225'''

|-
| 05:21
| Switch to the '''terminal''' for the solution.

|-
| 05:25
| Type as shown. Hence, we get the center of the image. Close this image.

|-
| 05:34
| You can also save the sliced image '''array''' to a new variable.

|-
| 05:39
| Type, '''img1''''' is equal to''''' img''''' inside square brackets '''''75 '''''colon '''''225 '''''comma''''' 75 '''''colon '''''225]''' Then to see the image type as shown.

|-
| 05:56
| Close this image window

|-
| 05:59
| We also know how to '''stride''' over an '''array.'''

|-
| 06:03
| For that we can drop alternate rows and columns out of the image.

|-
| 06:08
| Type, '''img '''''inside square brackets colon colon '''''2 '''''comma colon colon '''''2'''

|-
| 06:16
| To see this image, type as shown. We can see that the scale has reduced.

|-
| 06:24
| We can observe some '''blurring''' near the '''edges '''if you scale it down further.

|-
| 06:30
| Close the image window to return to the '''IPython console'''.

|-
| 06:35
| To increase the '''step''' to 4, type as shown.

|-
| 06:41
| Close the image window to return to the '''IPython console'''.

|-
| 06:45
| We shall use the '''Python.png''' present in the current '''working directory'''.Now we have an '''RGB''' image.

|-
| 06:54
| Let us slice the image and see what happens.

|-
| 06:58
| Type as shown. We can see the image.

|-
| 07:03
| Close the image window to return to the '''IPython console'''.

|-
| 07:07
| To check the dimensions of '''img''', we can use '''shape function'''.

|-
| 07:12
| Type, '''img.shape '''

|-
| 07:16
| The third number shows that there are 4 channels. These are corresponding to red, green, blue, and transparency value of the image.

|-
| 07:28
| The first number shows that the height of the image is 600. The second number shows that the width of the image is also 600.

|-
| 07:39
| Now we will slice the red channel of the '''array'''.

|-
| 07:43
| Type, '''plt.imshow '''''inside brackets''''' img '''''inside square brackets colon comma colon comma '''''0'''

|-
| 07:53
| Then type, '''plt.show '''''open and close brackets.''

|-
| 08:00
| We got the required red channel of the '''array'''.

|-
| 08:04
| Close this image.

|-
|08:06
| This brings us to the end of this tutorial. Let us summarize.

|-
| 08:12
|In this tutorial, we have learned to,

Read '''images''' into '''arrays''' and manipulate them.

|-
| 08:19
| Here is a self assessment question for you to solve

|-
| 08:23
| The shape of the variable '''img''' is (600, 600, 4).

|-
| 08:29
| What will be the shape of '''img1''' if '''img1''' ''is equal to'' '''img''' ''inside brackets colon colon ''2 ''comma colon colon ''4

|-
| 08:39
| And the answer is, (300, 150, 4)

|-
| 08:45
| Please post your timed queries in this forum.

|-
| 08:49
| Please post your general queries on Python in this forum.

|-
| 08:54
| FOSSEE team coordinates the TBC project.

|-
| 08:58
| Spoken Tutorial Project is funded by NMEICT, MHRD, Govt. of India. For more details, visit this website.

|-
| 09:07
| This is Priya from IIT Bombay signing off. Thanks for watching.

|}

Python-3.4.3/C3/Image-manipulation-using-Arrays/English-timed - Revision history

Pratik kamble: Created page with "{| border=1 | '''Time''' | '''Narration''' |- | 00:01 | Welcome to the spoken tutorial on '''Image manipulation using arrays'''. |- | 00:07 |In this tutorial, you will lear..."