Questions tagged [image-processing]

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6
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1answer
1k views

circle packing algorithm used by Percolator

I was admiring this rendition of the Mona Lisa from quasimondo's Flickr account. He says: Combining circle packing with data visualization. The pie charts show the distribution of the dominant ...
1
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1answer
50 views

How can you see which points in the spectrum is from which pixel in the original image?

Take the image and spectrum below. If I look at the spectrum, it just look like noise.... How to make sense of it intuitively? Image: Frequency spectrum of image (using Fourier Transform):
3
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1answer
2k views

What the difference between the Fourier Transform of an image and an image histogram?

Consider this small picture of a sunflower, and its histogram: What would the Fourier transform of the first picture look like? Is there any relationship between the histogram and the Fourier ...
9
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1answer
5k views

2D convolution: Flipping the kernel?

Why do we need to flip the kernel in 2D convolution in the first place? What's the benefit of this? So, why can't we leave it unflipped? http://www.songho.ca/dsp/convolution/convolution2d_example.html ...
3
votes
1answer
635 views

Identifying an object in an image based on color (AI ?)

First off, I am not sure if this is the correct stackexchange site to ask this question on, so moderators can feel free to move it. I am working on an application that identifies an object in an ...
6
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0answers
468 views

Space filling between random 2D lines

Note that I had asked this question in GIS forum, although it has gotten many up-votes, still has not received any answer. Hope you can break the silence, some collaboration :) Consider a region (...
11
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2answers
3k views

Why is the laplace transform not popular for image processing convolution?

Why is the laplace transform not popular for image processing convolution? Most textbooks only conver the Fourier transforms.
3
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2answers
152 views

Mathmatical way to represent an image kernel?

How to represent the calculation in this image mathematically? For example: With the discrete convolution $(f * g)[n]\ \stackrel{\mathrm{}}{=}\ \sum_{m=-\infty}^\infty f[m]\, g[n - m]$ and Fourier ...
11
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1answer
513 views

How to detect sunshine on a photo

How would you algorithmically detect for any given photo whether the sun was shining when the picture was taken? Examples A sample from this webcam at a mountain top: Clearly the sun is shining. ...
4
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0answers
355 views

Stereo images rectification and disparity: which algorithms?

I'm trying to figure out what are currently the two most efficent algorithms that permit, starting from a Left/Right pair of stereo images created using a traditional camera (so affected by some ...
2
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1answer
3k views

Image pattern detection - Finding similarities in same image

The problem: Only pattern-like images are supposed to be uploaded and be used as backgrounds to a site, photos should not. How would you detect if an image looks enough like itself to be regarded as a ...
2
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1answer
1k views

How do convolution matrices work?

How do those matrices work? Do I need to multiple every single pixel? How about the upperleft, upperright, bottomleft and bottomleft pixels where there's no surrounding pixel? And does the matrix work ...
3
votes
3answers
185 views

How center the eyes of human face at specific pixels?

I am facing a problem with processing some frontal facial images. I need to adjust the centers of the eyes (irises) to be at certain specific pixels in the image. In other words, i need to transform ...
1
vote
1answer
47 views

Transform inverse result

let us assume that: f is a grayscale image of size NxN, and F is the Fourier transform of f. G is a 2Nx2N transform obtained by inserting 0 between every value in F: What is the inverse transform ...
0
votes
2answers
1k views

median filter one after the other

Operate on an image by performing Median Filtering in a 3x3 window. Operate on the resulting image by performing, again, Median Filtering in a 3x3 window. Can the resulting image be obtained from a ...
2
votes
1answer
202 views

Contrast vs. Brightness question

As part of my homework I need to prove (or disprove) that changing the contrast and, then, changing the brightness is (or isn't) the same as changing the brightness and, then, changing the contrast. ...
2
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0answers
181 views

Compare vectors, photo mosaic

I’m trying to make a photo mosaic web application. I split the main picture in to a number of squares. I split this square up in to 9 squares (See picture) Then I calculate the mean color (RGB) of the ...
16
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3answers
32k views

What are the differences between computer vision and image processing?

What are the differences between computer vision and image processing? For example, in object recognition, what are the roles of computer vision and image processing?
7
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3answers
9k views

Shannon's entropy for an image

Shannon's entropy [plog(1/p)] for an image is a probabilistic method for comparing two pixels or a group of pixels.Suppose an image with a matrix of 3x3 has pixel intensity values ...
4
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2answers
821 views

Difference between HSI and YCbCr for pattern recognition by color

I am doing a project on face detection in C#. I want to find the skin area by using skin color segmentation. For that purpose, I have to extract the skin area. I know I can use HSI or YCbCr, but what ...
3
votes
1answer
149 views

Which Is a Better Way of Obtaining Scales, Gaussian Blur or Down Sampling?

In computer vision, scales are important when we carry out a scene analysis. Choosing different scales affect the result of the analysis. For example, if a face is relatively small in the scene, then ...