the size of picture show three data?

Question

bozheng 2024-1-16

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回答： Image Analyst 2024-1-16

As shown in the figure, I found that the call size results have three photos, but the question is how to view only one photo

the 20230814.jpg is below

So why multiply by 3? Any complete argument or reason? Thank you for your enthusiastic answers.

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Answer 1

John D'Errico 2024-1-16

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编辑：John D'Errico 2024-1-16

A black and white image typically has one channel only. All you need to know is how bright each pixel is.

But a color image stores typically red, green and blue channels. (Other color spaces can also be used of course.) But THREE channels. The jpeg image you show is a color image. Each pixel is represented by its corresponding red, green and blue code values.

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Steven Lord 2024-1-16

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John is exactly correct. For example, consider the peppers.png file.

[imagedata, colormapdata] = imread('peppers.png');
whos imagedata colormapdata
  Name                Size                Bytes  Class     Attributes

  colormapdata        0x0                     0  double              
  imagedata         384x512x3            589824  uint8               

Because the colormapdata variable is empty, that means imagedata has three planes of data: red, green, and blue. If we look at the image as a whole we can see all the colors.

figure

imshow(imagedata)

title('All channels')

But if we show just one channel, we only see that color. In the red channel, the green peppers are somewhat dark.

imagedataRed = imagedata;

imagedataRed(:, :, 2:3) = 0; % zero out the green and blue

figure

imshow(imagedataRed)

title('Red channel')

In the green channel, the red peppers are somewhat dark.

imagedataGreen = imagedata;

imagedataGreen(:, :, [1 3]) = 0; % zero out the red and blue

figure

imshow(imagedataGreen)

title('Green channel')

In the blue channel, both red and green peppers are dark. There aren't any blue peppers, but the white onions still show up somewhat.

imagedataBlue = imagedata;

imagedataBlue(:, :, 1:2) = 0; % zero out the red and green

figure

imshow(imagedataBlue)

title('Blue channel')

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Answer 2

Dyuman Joshi 2024-1-16

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It does not result in 3 images. That is a single image only, which is stored as a 3D array.

That is a RGB image, also referred as Truecolor image, stored as mxnx3 array.

Each page/plane of the array contains information regarding color intensity - the first plane in the third dimension represents the red pixel intensities, the second plane represents the green pixel intensities, and the third plane represents the blue pixel intensities.

https://in.mathworks.com/help/matlab/creating_plots/image-types.html#f2-12468