Image Intensity

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M@lik Ali 2012-6-4

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https://ww2.mathworks.cn/matlabcentral/answers/40195-image-intensity

评论： Image Analyst 2021-6-10

采纳的回答： Image Analyst

Hi all, Can any one tel me the command in matlab to calculate the intensity of image.

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Jean 2013-7-5

Does anyone further know how to do this for a specific area of pixels? For example, image(100:1:200,100:1:200) for a 100 by 100 pixel area, and get the intensity in this area as an average?

Image Analyst 2013-7-5

编辑：Walter Roberson 2014-2-11

在 MATLAB Online 中打开

meanGrayLevel = mean2(yourImage(100:200,100:200));

Don't use "image" as the name of your variable since it's a function.

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Image Analyst 2012-6-4

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https://ww2.mathworks.cn/matlabcentral/answers/40195-image-intensity#answer_49853

在 MATLAB Online 中打开

The mean of a particular pixel is just simply the pixel value, since there is only one sample - nothing really to take the mean of:

intensityValue = grayImage(100, 230); 
meanIntensityValue = mean(grayImage(100, 230));

Here, of course meanIntensityValue will equal intensityValue.

To get the mean of all the pixel values in the entire image, you can do any of these:

meanIntensityValue = mean2(grayImage);
meanIntensityValue = mean(grayImage(:));
meanIntensityValue = mean(mean(grayImage));

If you are using a grayscale image in which the values are "brightness" (as opposed to something like Hue), then the real unit would be closer to "brightness per pixel^2". Summing that over a number of pixels in a row or column would give you "brightness per pixel^2 * pixels" which would be "brightness per pixel".

... Brightness would not be the real physical unit. Eyes do not perceive brightness in a linear manner. https://www.pathwaylighting.com/products/downloads/brochure/technical_materials_1466797044_Linear+vs+Logarithmic+Dimming+White+Paper.pdf

"Approximate perceived brightness = sqrt(measured brightness)"

I just woke up, and digging into luminance and chromaticities and transfer functions this early in my day is making my brain hurt. @Image Analyst studied those things, so he would be in a much better position to talk about what the real physical units would be.

Image Analyst 2021-6-10

The usual nomenclature of your vertical profile (the image summed horizontally across columns) is "integrated gray value" and it will have units of gray levels. For a standard digital camera which measures illuminance Lux or irradiance (watts per square meter), the units of gray level correspond to units of energy (Joules).

(watts/m^2) * (area of pixel in m^2) * (seconds of exposure time) = joules.

Note that watts = joules/second so everything cancels out except for joules.

Note: units prefixed with "Phot" or "Lum" (like illuminance) refer to radiation in the visible range 400-700 nm. If it doesn't have a prefix or has "rad" prefix (like irradiance), then it applies to all energy across the whole electromagnetic spectrum.

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swetha Derangula 2017-8-5

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https://ww2.mathworks.cn/matlabcentral/answers/40195-image-intensity#answer_276931

编辑：Walter Roberson 2017-8-5

在 MATLAB Online 中打开

Is this code correct for entire image intensity? I didn't get any intensity value

clear all;
close all;
o=imread('450.jpg');
i=rgb2gray(o);
imshow(i)
intensityValue = i(100, 230);  
meanIntensityValue = mean(mean(i));

please suggets me

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Walter Roberson 2017-8-5

在 MATLAB Online 中打开

No code that contains "clear all" can be correct.

Your line

intensityValue = i(100, 230);

extracts one particular pixel's intensity, and only that one pixel. However,

meanIntensityValue = mean(mean(i));

should be fine for taking the mean intensity of the entire image.

Image Analyst 2017-8-6

You could also use mean2().

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Adina Stoica 2012-6-4

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在 MATLAB Online 中打开

Well, the intensity of the image is the average of the intensities of all pixels in an image (unless you're doing anything more specific than that). So if you do

mean(imagefile(:))

you should get the intensity of the image.

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M@lik Ali 2012-6-4

编辑：Walter Roberson 2014-2-11

在 MATLAB Online 中打开

Adina thanks for your response,

But actually i want to calculate the intensity value of all elements of the images.

someone told me like

intensityValue = grayImage(100, 230);

But in i have to calculate the intensity value of each pixel or total image, i think i can do it by calculating the intensity of each pixel and then add it but i am not sure.

Kindly help me about it..

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