What is Pixels and what is gray level value ? and how to calculate all distances between them

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Muhammad Tayyab 2020-2-9

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/504508-what-is-pixels-and-what-is-gray-level-value-and-how-to-calculate-all-distances-between-them

评论： Image Analyst 2020-2-10

采纳的回答： Image Analyst

7 by 7 matrix with entries 1 to 49.Each value is gray level of a pixel.

find the following distance between pixels with gray level 25 and 36.

uclidean Distance
City Block Distance
Chessboard Distance

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Answer 1

Image Analyst 2020-2-9

1
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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/504508-what-is-pixels-and-what-is-gray-level-value-and-how-to-calculate-all-distances-between-them#answer_414620

A pixel is an element of a matrix that represents something (like reflectance) of a certain scene. The gray level is the numerical valuke of the pixel. To find the distances between all possible pairs of pixels having gray levels 25 and 36 you need to first get the map of where those pixels are, then pass them into pdist2(). Since it sounds tremendously like homework, I'll give you hints so you don't get into trouble turning in my code as your own:

map25 = grayImage == 25;
map36 = ..............
[rows25, columns25] = find(map25);
xy25 = [columns25(:), rows25(:)];
distances = pdist2(xy25, ......................
    

That's pretty much it. Just fill out the code to get stuff for the 36 case and pass in the right distance method into pdist2, which is in the Statistics and Machine Learning Toolbox.

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Image Analyst 2020-2-9

Not sure what "I have get presentation" means. I guess it means you have to make a presentation of my code in front of your co-workers. OK, as long as it's not homework, try this:

% Create sample image with values between 25 and 36.
grayImage = randi([25, 36], 7, 7)
% Get a logical "map" of where 25 and 36 values occur.
map25 = grayImage == 25
map36 = grayImage == 36
% Get the coordinates of where the chosen gray levels are.
[rows25, columns25] = find(map25);
[rows36, columns36] = find(map36);
% Stitch together into two columns, which is what pdist2() wants.
xy25 = [columns25(:), rows25(:)]
xy36 = [columns36(:), rows36(:)]
% Get distances of every 25 point to every 36 points.
% Rows indicate the 25 coordinates, and columns indicate the 36 points.
distances = pdist2(xy25, xy36)
fprintf('Showing distances between the %d "25 points" with the %d "36 points".\n',...
	nnz(map25), nnz(map36));

You'll see something similar to this.

grayImage =

34 27 32 34 34 31 27

28 30 25 33 30 30 33

32 26 25 36 26 35 28

25 32 28 31 28 31 33

30 30 31 28 26 36 33

28 33 32 26 28 32 25

26 33 29 32 30 36 28

map25 =

7×7 logical array

0 0 0 0 0 0 0

0 0 1 0 0 0 0

1 0 0 0 0 0 0

0 0 0 0 0 0 0

0 0 0 0 0 0 1

0 0 0 0 0 0 0

map36 =

7×7 logical array

0 0 0 0 0 0 0

0 0 0 1 0 0 0

0 0 0 0 0 0 0

0 0 0 0 0 1 0

0 0 0 0 0 0 0

0 0 0 0 0 1 0

xy25 =

1 4

3 2

3 3

7 6

xy36 =

4 3

6 5

6 7

distances =

3.16227766016838 5.09901951359278 5.8309518948453

1.4142135623731 4.24264068711928 5.8309518948453

1 3.60555127546399 5

4.24264068711928 1.4142135623731 1.4142135623731

Showing distances between the 4 "25 points" with the 3 "36 points".

Muhammad Tayyab 2020-2-10

presentation means .. i am student and i have presentation on this topic in the class given by my teacher .. and i have to find the (1) chessboard distance (2) Euclidean distance (3) City block distance .... i have to create Code (Functions) for these formulas

Image Analyst 2020-2-10

My code gives the Euclidean distance, however pdist2() has other distance metrics you can use, like city block, etc. What is chessboard distance? How is it different than city block distance, which is the sum of the delta x plus deltay?

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