Generate data from a image plot with colour code as reference.

Hello, I am a naive user of Matlab, Please find the image attached. The image represents a Cp profile over a body. I would like to generate the data from this image. The grey line is my area of interest. My desire output is to generate Cp value (taken from the colour bar)at very point of that line with reference to y-axis.

[jonas]

It's possible. If the line is specified as user input, then extracting the color along the line is quite simple, althogh you will get some annoying artifacts due to the gray lines. Matching the colors to the colorbar should be fairly straight-forward.

With that said, it will require some work and it may be worth trying to get the source data instead. If the image is from a paper, I'd try contacting the author.

[Kushal Kumar]

Jonas, Thank you for replying,

May I know how can I specify the line as user input over an image like this? the image kept here is just an reference plot so that I can understand the concept and way to generate the data.

I have different set of the data for which I need use similar procedure to obtain the values.

[jonas]

Okay, I'll just make an answer explaining how I'd approach this.

Answer 1

[jonas]

I'd approach this by the following steps.

load image with axes and everything:

I = imread('FileName.png');
imshow(I)

Get start and end-points of the line as user input

[xi,yi] = getpts
y = min(yi):max(yi);
x = xi(1).*ones(size(y))

Get colors of each point

z = I(y,x,:)

Now you have the colors stored in z, you need to connect these colors to the colormap. Since the colorbar is defined in discrete steps, I would repeat the above procedure for the colorbar, asking the user to input a single coordinate for each color. Then you will have a type of conversion sheet so that you can connnect the colors of your line to the values from the colorbar. That's about it.

[Mahdi Bashiri]

Could you help me how can I get the data of a generated plot by Matlab without saving the file itself?

So, I need to use imread command. As an example imread(sin(x))?

Thanks for the help in advance.