Finding the RGB value of a .fig at given X and Y locations

Hello there may be a really straight forward way to do this that I can't work out but basically...

I want to open up a matlab figure which looks like this and be able to find the RGB values at specific X and Y coordinates that I enter for example x = -122.078519830603 y = 59.3516220639968.

I can do something like this with the data cursor but I have a large number of x and y locations that I need the RGB values for and so would like to write it into my code.

Thanks for any help!

[Muhammad Usman Saleem]

tell me whether it is a map or rgb image?

[Adam]

You will likely have to use interpolation on the loaded images as I would assume there is not a pixel at exactly x = -122.078519830603 y = 59.3516220639968.

[Madeleine Groves]

Hi Muhammad it's a map. I run a script that produces this colormap from my data (a .fig file). I don't want to save it as an image file as I want to use the specific X and Y values to get the color data at that point on the map.

[Muhammad Usman Saleem]

see my answer below. Firstly save this map in tiff or jpeg format and then try my solution

Answer 1

[Chad Greene]

I wrote colorpicker to get rgb values from mouse clicks on a figure. You could modify colorpicker to use specified coordinates instead of mouse clicks.

[Madeleine Groves]

Thank you your clickz function does what I was wanting to do without having to find what z value the RGB relates to and has solved my problem.

Answer 2

[Muhammad Usman Saleem]

x=imread('YourImage');

• Images are matrices (2D if grayscale, 3D if colored) in MATLAB.
• You can use x(i,j) to access a pixel at location (i,j) in a grayscale image.
• If the image is colored, you can use x(i,j,:) to access the r, g, b values in a 3-vector, respectively. If you need individual channels, then, you can use x(i,j,1) for red for example.
• You may read to learn this page more.

[Muhammad Usman Saleem]

Here is the function (you must save this script to drive where the image is) which demand from you x,y position and in return give you RGB at this location.

Here is a function in which you enter coordinates (x,y) and it wil return you RGB value at this coordinate.

   function rgb=getRGB(x,y)
    Im=imread('YourImage.jpg'); % Give here your image
    rgb=Im(x,y,:);
    end

Here i am trying for my 'payment.jpg' image

>> rgb=getRGB(10,30)

rgb(:,:,1) =

    124

rgb(:,:,2) =

    125

rgb(:,:,3) =

     93

First is brightness value for R, second for G, third for B.

Accept this answer you satisfy with results

[Adam]

This will work for integers, but not so much for the example given in the question of x = -122.078519830603, y = 59.3516220639968

[Muhammad Usman Saleem]

what is your prescription about -x,-y?

It is coordinates of the frame in which image has open. Are you know georeference image/ Ungeoreference image??

This function run smoothly for all inputs even on -x,y, if gray value at this location exited! You are trying to get where there no DN value at this location! @Adam

[Adam]

Well, I don't know what the author of the question has in mind, but it seems clear some sort of interpolation has to be done if they want to query such a specific point because it will not exist on the grid, even if negative integers are appropriately shifted to be interpreted as indices into the image.

I assume that a value is still required to be calculated for these cases rather than just a "no value exists at this location" type of error.

Answer 3

[Image Analyst]

You can use impixelinfo() to have a little status bar on your GUI that gives you the x and y and RGB values as you mouse around the image. It's easy - I do it all the time.

[Madeleine Groves]

I had seen that method of doing it, the problem is I have about 100 locations I need to find the RGB values for at very specific location that are difficult to target with the mouse.

Do you know of a way of using impixelinfo or something like it in a script so I can enter the X and Y coordinates and have the RGB value returned?

[Muhammad Usman Saleem]

see again above my answer @Madeleine Groves

[Image Analyst]

If you know the coordinates in advance, just hard code them in, like Muhammad showed.

[Muhammad Usman Saleem]

@Image you are my teacher. I want to learn from you a lot of new stuff..

Stay bless always