CODEWITHSUNDEEP
image-processingmatlab
Christina
Christina

Reputation: 935

Resizing image in specific case

I have an image of size 260 x 260 pixels. I know how to resize it to 140 x 140 pixels for example and then convert it to grayscale. Let us assume the matlab code below: 

image = imread('my_image.jpg');
image_resized = imresize(image, [140 140]);
size(image_resized) % 140 x 140 x 3
image_gray = rgb2gray(image_resized);
size(image_gray) % 140 x 140

What I want is a specific case. I am interested to normalize the image to 140 pixels in height where width was rescaled accordingly so that the image aspect ratio was preserved. Unfortunately I don't know how to edit my above code.

Any help will be very appreciated.

Upvotes: 1

Views: 1455

Answers (2)

Divakar
Divakar

Reputation: 221564

Try this -

image = imread('my_image.jpg');
desired_height = 140;

%%// Width of the resized image keeping the aspect ratio same as before
n2 = round((size(image,2)/size(image,1))*desired_height);

%%// Resized image
image_resized = imresize(image, [desired_height n2]);

Edit 1

NOTE: Alternatively you can use the size prescribed by imresize using NaN as suggested by Shai's solution too, but it ceils or rounds up the sizes, which you might not want in most of the cases.

To prove this case, I tried imresize to keep the height as 173, I got different sizes with manual resizing as opposed to when I let imresize decide the sizes.

Code used for the experiment

%%// Resized image
image_resized_with_auto_sizing  = imresize(image, [desired_height NaN]);
image_resized_with_manual_sizing  = imresize(image, [desired_height n2]);

The size outputs for my experiment -

>> whos image_resized_with_manual_sizing image_resized_with_auto_sizing
  Name                                    Size               Bytes  Class    Attributes

  image_resized_with_auto_sizing        173x185x3            96015  uint8              
  image_resized_with_manual_sizing      173x184x3            95496  uint8

Notice the difference in width for the two cases. This issue is discussed here too.

Upvotes: 1

Shai
Shai

Reputation: 114796

You can use NaN is the desired size argument to indicate exacty what you want

image_resized = imresize( image, [140 NaN] );

Which basically tells Matlab "don't bother me with the image's width - figure it out yourself!".

See imresize documentation for more information.

Upvotes: 2

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