How to find out location where temperature is high based on color graph using Matlab?

Sir, Need your help. It's a sea shore image. I have to find out the location where the sea surface temperature is high based on color value variation (color graph is attached with the image), from the rgb image.

(ie, if an area contains high red value then the sst is 33.5 which is very high in this particular location)

Note: The color scale displayed beneath the image just relates the colors in the image. which is just a color scale which defines---> if this color then this will be the temperature value.

(eg: if blue color in the rgb image,it will just aware us that the temperature is low).

[Antony Joseph]

Hi Arun. Did you get the proper answer for this question? If you have please help me. because I have this same problem.

[Rik]

@Antony There are 3 answers to this question. Do none of them work for your problem?

[Antony Joseph]

@Rik- My thermal video is not from the camera. this video I extracted from my Simulation. I am using Simufact software for my simulation. After the Analysis I will get Simulation result video. From that video, I have to do postprocessing. That's why I am importing that thermal video to Matlab and would like to find temperature from each frame. I have to find the maximum temperature in each frame. Now my video has 820 frames. How could I find the maximum temperature in each frame? actually, my every frame has different high and low temperature. How can I do that one? How can I apply to every frame?

Now, In my Matlab, I am reading each frame continuously from the video. actually along that each frame, I should have to find the maximum temperature. Then I can plot Maximum temperature vs frames graph. actually, Finally, I have to get this temperature vs frames graph from the whole video(820 frames).

[Antony Joseph]

@Rik- Could you please help me?

[Antony Joseph]

my temperature range: 20-degree Celcius - 713.07-degree Celcius

Answer 1

[Jan]

If you have an RGB image and a colormap (which seems to be the case), you can convert it to an indexed image:

IndexImage = rgb2ind(RGB, map)

Now IndexImage is a a 2D matrix containing the indices related to the color map. Now simply search the maximum value:

[maxIndex, pos] = max(IndexImage);
[y, x]          = ind2sub(size(IndexImage), pos);

Or you can create a mask for values above a threshold:

mask = IndexImage > 75;  % Example
figure;
imagesc(mask)

If you want to set the limit to 33.5 degree, you have to find out to which index of the colormap this value belongs. For an explicit suggestion, we need to know how your colormap is defined.

[ARUN V]

    % code
 RGB = imread('i.png');
figure
imagesc(RGB)
axis image
% zoom(4)
[IND,map] = rgb2ind(RGB,32);
figure
imagesc(IND)
colormap(map)
axis image
% zoom(4)
[i,j]=ind2sub(map,IND);

But sir, output of this code produced didn't match the output expected.. I am new to matlab, need help...

[Jan]

Please attach the input data and explain, what you expect. Maybe the Matlab code works reliably and only your expectations are the problem?

Answer 2

[Rik]

1. crop to the relevant part (remove axis and dashed lines)
2. convert to indices with rgb2ind
3. use [r,c]=find(A_ind==min(A_ind(:)); (or ind2sub) to get the location(s).

[ARUN V]

 #code
RGB = imread('i.png');
figure
imagesc(RGB)
axis image
% zoom(4)
[IND,map] = rgb2ind(RGB,32);
figure
imagesc(IND)
colormap(map)
axis image
% zoom(4)
[i,j]=ind2sub(map,IND);

But sir, output of this code produced didn't match the output expected.. I am new to matlab, need help...

[Jan]

qARUN V: We cannot know, which output you expect. I suggest to open a new thread and to explain the details.

Answer 3

[Image Analyst]

I've already done exactly that for someone else. Take the attached m-file and make the obvious changes.

[Antony Joseph]

Hi Image Analyst, From this example I got how we can create IndexImaege. but you did not explained how we can find maximum temperature from that frame? Could you please help me? Now I am doing my thermal video converting to frames. and from that each frames I have to find maximum temperature value. because I have to find a distance vs temperature variation graph from that video.

[Image Analyst]

That was an old script. I've made changes since then. I've edited my question above to give the updated code and screenshot. Download them and try it.

[Antony Joseph]

Thank you Image Analyst, That example helped me a lot. But I have one problem also: In your example, you found a maximum temperature from one frame. but you gave in the script already high and low-temperature values. after that, you found the maximum temperature. Now I am doing my thermal video converting to frames. and from that each frame I have to find maximum temperature value. but the problem is, in each frame my high and low temperature is different. that's why I could not able to find maximum temperature from each frame. Could you please help me with this problem?

[Image Analyst]

That does not matter. All that matters is that the total possible scale - the dynamic range - stays the same. You should be able to lock that down with your camera. Then the actual temperatures in the field of view can be anything inside that range.

[Antony Joseph]

But my thermal video not from the camera. this video I extracted from my Simulation. I am using Simufact software for my simulation. After the Analysis I will get Simulation result video. From that video, I have to do postprocessing. That's why I am importing to Matlab and finding temperature from each frame. I have to find the maximum temperature in each frame. Now my video has 820 frames. I did same as you did but I am getting the same temperature from each frame. because I put in the script only one high and low temperature. actually, my every frame has different high and low temperature. How can I do that one? How can I apply to every frame?

[Image Analyst]

To apply to every frame, see my attached demos.

Adapt one of them as needed to measure the temperature frame by frame. Your simulation should have some knowledge of the range of temperatures. I mean you can just make a video and have the range be -200 to -50 on one frame and then 3000 to 5000 degrees on the next frame. You must know what range they fall into. Again, you don't need to know the max - just the range, even if the max does not hit the top of the range.

[Antony Joseph]

@ImageAnalyst- My thermal video is not from the camera. this video I extracted from my Simulation. I am using Simufact software for my simulation. After the Analysis I will get Simulation result video. From that video, I have to do postprocessing. That's why I am importing that thermal video to Matlab and would like to find temperature from each frame. I have to find the maximum temperature in each frame. Now my video has 820 frames. How could I find the maximum temperature in each frame? actually, my every frame has different high and low temperature. How can I do that one? How can I apply to every frame?

Now, In my Matlab, I am reading each frame continuously from the video. actually along that each frame, I should have to find the maximum temperature. Then I can plot Maximum temperature vs frames graph. actually, Finally, I have to get this temperature vs frames graph from the whole video(820 frames).

[Antony Joseph]

@ImageAnalyst- Could you please help me?

[Antony Joseph]

my temperature range: 20 degree celcius - 713.07 degree celcius

[Antony Joseph]

<<

>>

This Image frame I just took from my thermal simulation video.

Here temperature range: 20-degree Celcius to 84.02 degrees Celcius.

This video has 225 frames. I have to find the maximum temperature in each video. Then I can plot Maximum temperature vs frames graph.

script:

% This will probably be the high temperature.

highTemp = 84.02;

% This will probably be the low temperature.

lowTemp = 20.05;

thermalImage = lowTemp + (highTemp - lowTemp) * mat2gray(indexedImage);

maxTemperature = max(thermalImage(:));

I was following this code but I am getting the same maximum temperature in each frame.

That is my problem.

could you please help me?

[Antony Joseph]

You can see from this matlab result, The maximum temperature in each frame is same value(84.02).

how can I solve this problem?

[Walter Roberson]

you do not appear to have cropped the color bar out of the images before looking at the maximum

Answer 4

[Özgür Uzunkaya]

ExtractMovieFrames.m What does the file and the following files say? where can i use it?

[Rik]

@Özgür Uzunkaya, how exactly does this answer the question? What exact file are you referring to?

Have a read here and here. It will greatly improve your chances of getting an answer.

[Walter Roberson]

https://www.mathworks.com/matlabcentral/answers/377055-how-to-find-out-location-where-temperature-is-high-based-on-color-graph-using-matlab#comment_595688 has the code.

[Image Analyst]

@Özgür Uzunkaya I wrote the attached, well commented program. If you have any questions about it let me know what lines they are and I'll improve the comments.

You may not want to do everything in the demo, for example asking the user if they want to save each individual movie frame. Just delete the parts you don't want and make any other modifications you want.

I have lots of other movie demos. I've attached some of them if you want them.