Image Intensity

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M@lik Ali 2012-6-4

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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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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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