Hello I need a code that gives me the local minimum of a histogram please ?

I created 12 histograms for 12 frames and I need to get the local minimums of these histograms.

Answer 1

[Mathieu NOE]

hello

maybe this

the local minima are the red diamonds

x = randn(1000,1);
h = histogram(x);

Values = h.Values;  
BinCounts = h.BinCounts;  
BinEdges = h.BinEdges;
BinWidth = h.BinWidth;
centers = BinEdges(2:end) - BinWidth/2;

% find min values 
ind = islocalmin(Values);
hold on
plot(centers(ind),Values(ind),'dr');
hold off

[AbdelRahman Mostafa]

I tried it but it didnt work. There is an error in line 2 (undefined function histogram).

[Image Analyst]

You must have a super old version. histogram was introduced in r2014b. What does this say

which -all histogram

If it says you don't have it, then use its predescessor hist(). But then, all the code after that won't work either, like islocalmin() because that came later. If you have the Image Processing Toolbox you can use imregionalmin() on the histogram to find the local mins. Otherwise you can use findpeaks() in the Signal Processing Toolbox to find valleys (just negate your histogram before passing it to findpeaks).

[Mathieu NOE]

hello

this is a "stone age" version of the code (created and tested under R12.1 from 2001 !!!)

x = randn(1000,1);
bins = 25;
[Values,centers] = hist(x,bins);
bar(centers,Values,'hist');

%% find max / min values (alternative to islocalmin / islocal max
Values = Values(:).'; % just to make sure the data is a column vector
dif  = diff(Values);
dif  = [dif(1:end-1) .* dif(2:end) <= 0,0] .* dif;
mins = 1+find( dif < 0 );
maxs = 1+find( dif > 0 );
%%

hold on
plot(centers(mins),Values(mins),'dr',centers(maxs),Values(maxs),'dg');
legend('local mins','local maxs','data');
hold off

[AbdelRahman Mostafa]

Thank you

[Mathieu NOE]

Do you mind accepting my answer if it fullfills your expectations ?

tx

[AbdelRahman Mostafa]

I will explain to you exactly what I want:

I imported a video in matlab and did histograms for 12 frames of that video. I want to get the local minimums of each of the 12 frames. If you could help me I'll be very thankfull.

[Mathieu NOE]

hello

so how does the video data histograms look like ? have data to share ?

[Image Analyst]

I don't see why his code should not work on each of your frames. What kind of help do you need? Just put his code into the loop over frames.

What will you do with the local min and max info once you have it? If the histogram is noisy, as they usually are, you'll have lots of min and max locations. What do you plan on doing with that info?

[AbdelRahman Mostafa]

clc

clear all

close all

v = VideoReader('fog.mpg');

n=100;

b=double(rgb2gray(read(v,1)));

for i=2:n

cf=double(rgb2gray(read(v,i)));

diff=cf-b;

c=2*(diff>0)-1;

b=b+c;

end

for j=1:30:349

ccf=double(rgb2gray(read(v,j)));

Di=abs(ccf-b);

figure

imshow(Di);

e=imhist(uint8(Di));

end

[AbdelRahman Mostafa]

This is the code that I wrote. I just need to get all the local minimums of the histograms. Thank you

[Image Analyst]

So the "why you need it" is a closely held secret? You basically said you need it because you need it. Let me challenge you and say that you don't need it to do whatever mysterious thing you're attempting to do. Prove me wrong.

Anyway you can use imregionalmin and imregionalmax to find min and max locations in a signal.

[AbdelRahman Mostafa]

I am a masters student and my thesis is about image processing. I just needed to know how to get the local minimums to be able to continue my thesis. Now you know why I need it. If you can help good if you cant then dont talk to me that way. Thank you