Questions tagged [histogram]

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Multivariate Histogram Matching for Image Color Matching

Suppose X is random variable that is spatial position in finite range, which its Cumulative Distribution Function (CDF) could be calculated easily, then if I have two random variable X and Y spatial ...
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22 views

How to solve this math problem regarding Histogram matching?

Please help solve the problem in the picture. I am confused due to the piecewise nature of the density functions. If it was a simple curved PDF, I would simply integrate over full range and use the ...
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8 views

quantification of histogram equalization improvement

My project consist of classification of images using ML. The images are microscopic slices. For the feature extraction phase, I am using multiple filters and got a good result. So I decided to do a ...
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17 views

Which are the rules of choosing a target image for histogram matching?

With histogram matching we can transform an image's intensity distribution. But this idea is very subjective. Sometimes for choosing a target image we have options no better than a guess. But is their ...
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12 views

Computing White Speckle Metric in a Document Image

The paper 'Metric-based No-reference Quality Assessment of Heterogeneous Document Images', discusses about measuring the quality of characters in a document image. I'm having difficulty to understand ...
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1answer
67 views

'Combed' Histograms

I have two FLIR Blackfly cameras that are identical outside of one being color and the other being mono. I set the ADC of both to 10 bit, and save the images in 16 bit. This results in the combed ...
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1answer
43 views

Making images taken under daylight conditions appear as if they were taken at night using image processing elementary techniques

I know that these days' style-transfer GANs should be able to style-transfer day images into night images. I however prefer to do it using a set of elementary image processing manipulations, so I can ...
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2answers
69 views

Lightweight test for bimodal distributions?

Here, and in the stats stackexchange, seem to be answers that reference tests for bimodal distributions that involve iterative binning or iterative curve fitting methods. However "eyeballing" a plot ...
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2answers
52 views

How to plot histogram of difference of two images using MATLAB

i would like to calculate difference of two images. Then, histogram of difference of two images. So I can plot a histogram but I am not sure whether it is true or not? Also, I am not sure about what ...
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36 views

I can't implement plateau limit histogram equalization algorithm using MATLAB

i tried to implement this research paper using MATLAB. Unfortunately, my result is not same with the original result. Here is my try step by step: ...
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4answers
407 views

What Information Is Lost by Histogram Equalization?

I cannot think of a way to restore an original image after histogram equalization. But this latter seems to "enhance" (= increase contrast of) the image's details. What information is then lost by ...
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1answer
43 views

MATLAB Image-Processing Toolbox: asking for a roadmap!

I plant trees in the north of BC for a living and have next to none sp experience, please be gentle :^] TLDR: The problem is essentially this: tracking and calculating the "height" of three ...
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2answers
103 views

What Is a Weighted Local Histogram?

I'm reading through a couple of academic papers, and this terms often comes up "local weighted histogram". An example of quote is the following: First, cumulative histograms are built for every ...
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1answer
97 views

Harmonics in Quantal Histogram

I'm studying what I believe to be a system that produces a (noisy) quantal response (i.e. there should be a minimum increment of response). To do this, I've plotted a histogram of some ~6000 amplitude ...
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1answer
112 views

Image Histogram - What Is the Interpretation of PDF

For digital images (assume 2D gray scale image), the normalised intensity histogram is often treated as the probability distribution function of the intensity ie., intensity is treated as a random ...
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1answer
88 views

From Uniform to 2D gaussian

I have a 2D uniform distribution. I would like to assign probability-weights in the distribution, according to the standard deviation to convert the distribution into a 2D gaussian. I know how to do ...
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1answer
122 views

Image Contrast Enhancement Threshold Selection

I have a a set of 24bit images with bright reflective spots washing out the underlying detail. While I'm interested in tone mapping algorithms, since these bright spots are purely noise I would like ...
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2answers
211 views

Histogram Counts of a 2d Matrix

I am currently working on a project in which I have a 10 x 2 matrix: A. I want to find the top 3 number of occurrences of each row using MATLAB. ...
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90 views

Applications for adaptive and non adaptive histogram equalization

I have a question regarding histogram equalization and adaptive histogram equalization. In which circumstance would it be preferable to use adaptive histogram equalization over histogram equalization ...
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1answer
323 views

Entropy of enhanced image more than the original image

It is said that the entropy of an image is the information that it contains. Let us assume, that the entropy of an image f(x,y) is ...
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1answer
121 views

Histogram estimation (from sub-set of image pixels)

Problem: How to find gray-scale image histogram without iterating all pixels and binning them. Description: Suppose that I have large set of images with no common scene and of different resolutions. ...
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1answer
829 views

Histogram Equalization Ignoring zero in Python

I wrote a small python code for histogram equalization (ignoring zero values) for an image but it is taking too long to run. Code is written with reference to wikipedia article on histogram ...
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1answer
1k views

Python: How to calculate image perimeter orientation histogram?

I would like to find the perimeter orientation histogram of an object inside an image. The object is returned into an array but I don`t know how to find the orientation of its perimeter. I think the ...
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0answers
62 views

Watermark insertion process in image

I'm new in the field of image processing and I'am trying to implement a watermarking algorithm (for medical images in DICOM format) based on this paper. As written in the paper, this algorithm is ...
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2answers
398 views

How to Generate a vector map for histogram equalization

Assuming I have a gray scale image Im with $0:255$ levels of gray, I want to generate a vector map that will preform a histogram equalization on the image. I have ...
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2k views

Measuring sharpness/contrast for autofocus

For the implementation of an auto-focus for the raspberry cam I need some measure of image sharpness. I used the following sample picture: The first approach was to compute the shannon entropy of the ...
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1answer
107 views

Histogram Equalization

I am reading the etext on Digital Image Processing by Gonzalez and under the section on Histogram Equalization, an equation which is apparently basic is shown. I have no clue what the equation means ...
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2answers
202 views

MATLAB: get members of histogram populations EXCLUDING those inbetween

The Problem I have a (noisy) square wave signal and need to extract the data points that make up the 'baseline' and 'plateau' ONLY. I do not want data from the rise and fall. So far I have ...
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1answer
601 views

How to detect whether a signal is unimodal or bimodal?

I have to kinds of signals. The first type of signals are such that their histograms are unimodal (one-peaked). The second type of signals are such that their histograms are bimodal (two-peaked). How ...
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1answer
79 views

How to gather similar objects in an image?

I am working in a traffic tracking app, I am using a background subtraction approach to obtain information about the moving vehicles. After some morphological operations I obtain blobs of the moving ...
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1answer
191 views

Equalization and then Sharpening vs Sharpening and then Equalization

This was a question from an exam of digital image processing: "Working with low contrast images, an elective method to enhance details and improve contrast is to apply in cascade an equalization of ...
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2answers
605 views

CLAHE - Redistributing excess pixels among histogram bins

In order to clip an image's histogram to a maximum value, according to the CLAHE algorithm, the excess pixels (above the clip limit) will be distributed equally among all the histogram bins (While ...
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1answer
5k views

Histogram matching (specification) in Python

I'm trying to implement an algorithm in which I first pad each row of the image with a fixed amount of new pixels in a certain range, apply Gaussian smoothing to the row cumulative histograms in ...
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0answers
139 views

How do i detect if an image has a gradient or not?

I have coloured images, some may be just clipart, some may be artwork, both could be with or without gradients. Before i run a colour counting algorithm on them, i want to detect if the image has ...
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1answer
93 views

Noise in Digital image

in Digital Image Processing restoration ,from my understanding after reading articles , it's seems that the noise must be dominant in the histogram of the image , which is make it possible , to get ...
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1answer
520 views

Does anyone know how to overlay a equalized CDF plot with equalized histogram in matlab?

I am willing to overlay a equalized cdf with equalized histogram in matlab. But it's really hard to find any recommends. so if you can, would you please let me know about that?
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1answer
453 views

Getting 16 bit image statistics in Photoshop

The histogram in Photoshop for a 16-bit image downsamples to 8 bits, showing a tonal range of 0 to 255. I appreciate to show tonal ranges for a 16 bit image a horizontal zoom function would be ...
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117 views

Gonzalez question solution

If I have the histogram of an input image as Gaussian probability density function of the form: $$P_r(r)=\dfrac{1}{\sqrt{2\pi}\sigma}e^{-\dfrac{(r-\mu)^2}{2\sigma^2}} $$ where: $\mu$ and $\sigma$ ...
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1answer
3k views

Histogram Intersection with two different bin sizes?

I have two images: A and B. Image A is a screenshot of image B, the original image. While there is noise in image A, the original features are still distinguishable. Histogram intersection tells us ...
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3answers
142 views

float image to integer type image

I have a multispectral satellite image and I would like to "transform" each of the image bands into one with integer values. For example to stretch? the image between 0 and 255. Not sure how to ...
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1answer
13k views

Histogram matching of two images using cdf

I have already calculated the cdf values of each image now i have to map the reference image values to target . I cannot use histogram equalization or interpolation I simply have to map them . ...
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1answer
2k views

Histogram and binary image in opencv? [closed]

I would like to compute how many zeros and ones (e.i. 255) in a binary image. The following code to generate a binary image by using Matlab. ...
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0answers
454 views

GLOBAL THRESHOLDING using histogram

There is a recursive way of finding threshold in the image using histogram that are biomodal, and is as follows: An automated procedure for bimodal histograms : Select an initial estimate of T ...
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1answer
1k views

What steps come after finding the gradients of the SIFT key points?

I am using a SIFT algorithm to extract features from an image. I understand that the SIFT descriptor first finds the extrema and then finds the gradient and direction of each of these interest points....
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573 views

Distance-metric for SIFT descriptors matching

Will using Cosine-Similarity or Histogram Intersection as distance-metric, for matching SIFT descriptors, help to get better results? Anybody tried on that ever?
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2answers
576 views

How to create a band limited signal of sine waves that is nearly uniform distributed

I would like to create a signal that is nearly uniform distributed (as depicted in Figure 1). It must consist of some single sine waves (e. g. 400 Hz, 430 Hz, 500 Hz) or a random band limited signal (...
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163 views

Encoding the HOG features

I have got a video containing 200 frames and i am extracting low level features at pixel level. Then i am dividing the entire frame in to small spatial patches (say of size 7x7) and creating a feature ...
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4answers
7k views

Why is histogram equalization called as “equalization”?

When output histogram is not same as reference histogram, why is the method called histogram equalization? For example below are two figures from http://en.wikipedia.org/wiki/Histogram_equalization. ...
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1answer
775 views

Image Contrast Enhancement based Sub-histogram Equalization Technique without Over-equalization Noise

I'm a computer science student and I have an assignment requiring me to implement the algorithm proposed by this paper but I'm hitting a roadblock trying to understand the implementation of one of the ...
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2answers
2k views

Calculating an HSV histogram

I have to compute an HSV histogram of a colored image. Is it same as an H-S histogram? I have found H-S histogram computation code everywhere. What is the method to change an H-S histogram to an ...