How to convert image pixels values to the temperature values?

Hello,

How to convert image pixels values to the temperature values?, in image I found pixel value, like 255, and I know that it match 37,4 C, how to export that value to the screen?

Answer 1

[Image Analyst]

You have to convert your entire image to a floating point image knowing at least two temperatures, not just one. Just because 255 = 37.4 does not tell us what what temperature zero gray levels is at.

After that

imshow(temperatureImage, []); % Use [] because it's floating point
impixelInfo('Position', [x,y,width,height]);

impixelinfo() will let you mouse around the image and it will report the temperature on your GUI.

[Dovile]

I have two points, 0 pixels = 23.1 C, and 255 pixels = 37,4 C, I need to get intermediate proportional values, and I need, that matlab it automatically calculate, and derived each pixel temperature value.

[Image Analyst]

So why don't you just scale it like you'd intuitively expect

temperatureImage = (grayImage / 255) * (37.4-23.1) + 23.1;

Makes sense to me. Isn't that what you thought of too?

[Andy Smith]

Since I want to report this method in my thesis, kindly let me know the technical name of this method. Is it the Histogram Shrinking? Thanks in advance.

[Guillaume]

Huh? It's one of the simplest mathematical operation: a linear transformation

y = a*x + b

Also known as scaling in this context.

[Andy Smith]

Thanks for your reply, Guillaume.

[Mateo Ramirez]

Dear Image Analyst,

I know two temperature for my image (highest and lowest) how can I convert my image to a floating point.

Best regards, MRa.

[Image Analyst]

MRa:

temperatureImage = mat2gray(yourImage) * (highTemp - lowTemp) + lowTemp;

[Mateo Ramirez]

Thank you very much Image Analyst,

For some reason I didn't receive any notification on your reply.

MRa.

[Mateo Ramirez]

Dear Image Analyst,

I might be missing one step, converting my image to a Matrix (mat). If this is correct can you explain me please why should i do that? Below the code piece of code i used and attached the picture I am trying to analyze:

image = imread('IR71.png');

[I2, rect] = imcrop(image);

temperatureImage = mat2gray(I2) * (36.9 - 23.2) + 23.69

gray = mat2gray(I2);

imshow(gray)

With your previous uploaded tutorials I was able to identify the hottest point in the "Photovoltaic Panel" I want now to print the temperature of this zone right next to the "Hot Point". With this first piece of code" [I2, rect] = imcrop(image)" I am making my life easier just before adding it to the full code.

Looking forward to receiving your comments, Best regards, MRa.

[Image Analyst]

You need to convert the colors into a temperature. You can't do that just by your formula. It's not that easy. See my attached demo.

[Alaa Eddin Ziadah]

Dear Image Analyst,

i am trying to run your code withe my thermal image(see attach), but i become always an error:

>> rgbImage = originalRGBImage(imageRow1 : imageRow2, imageCol1 : imageCol2, :));

Index in position 1 exceeds array bounds (must not exceed 120).

can you please help me.

[Image Analyst]

Sure. Start a new question and attach your image and code. You probably did not update the rows and columns to crop the proper part of the image.

[Bipasha Kundu]

Hello Sir,

I am working on a project which is quite similar to this. I would like to know how to get the High and Low temperature. Thank you

[Image Analyst]

@Bipasha Kundu to get the max and min temperature you can use max() and min() on your temperature image:

maxTemp = max(temperatureImage(:));
minTemp = min(temperatureImage(:));