14
votes
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$8 \times 8$ block matrix in JPEG image compression?
The lossy JPEG compression does not merely remove small coefficients in higher frequencies. It encodes them with a precision relative to a (relatively crude) visual perception model; most notably, ...
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14
votes
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Auto Detection of Rotation Angle on Arbitrary Image with Orthogonal Features
If I understand your method 1 correctly, with it, if you used a circularly symmetrical region and did the rotation about the center of the region, you would eliminate the region's dependency on the ...
- 12.3k
13
votes
Accepted
Does a simple photograph contain more information than a complex painting?
It depends how you define the term "information" or "entropy".
The conventional definition of entropy of an image is to think the image as a two-dimensional matrix of pixels and
$$H = - \sum_k p_k \...
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8
votes
Who is Barbara (test image)
The appeal of this image is obviously in the numerous lines, which test the aliasing properties of resizing, denoising, and super-resolution algorithms.
It seems Allen Gersho is the source, according ...
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8
votes
What Is the Difference Between the Terms Color Intensity and Color Saturation?
When you take an RGB Image matrix and convert the color into HSV Color Model the color is represented on Cylinder.
Now, the intensity (Lightness / Value) is the height on this Cylinder which is going ...
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7
votes
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What does the 420 means in YUV420?
The 3-digit number describes the subsampling of the
chroma (U and V) channels. A detailed explanation is at
http://en.wikipedia.org/wiki/Chroma_subsampling
In particular, YUV420 means that the U ...
7
votes
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Why Wavelet based Transform Is More Suitable for Image Compression Compared to DCT?
Both JPEG and JPEG 2000 use the change of basis compression type.
Namely, we transform the data into a different representation assuming in this representation the number of parameters needed to ...
- 39.1k
7
votes
Best way of segmenting veins from arm?
So one good step to enhance the vein-like structures is coherence enhancing diffusion:
Weickert, Joachim. "Coherence-enhancing diffusion filtering." International Journal of Computer Vision 31.2-3 (...
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7
votes
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What's the Difference Between UQI and SSIM Measures for Image Similarity / Quality?
The developers of both are the same hence the similarity is indeed "By Design".
The only difference is the addition of 2 constants in SSIM (C1 and C2).
The UQI:
The SSIM:
As the writers write in ...
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6
votes
How does salt and pepper noise occurs in an image
Salt-and-pepper noise is a form of noise sometimes seen on images. It presents itself as sparsely occurring white and black pixels.
In another words ( in the sense of pixels), salt and pepper noise ...
6
votes
Accepted
How Can I Remove Flickering Background in a Video?
For those classic Video Processing operations there is nothing better than the Plug In's of AviSynth.
Specifically for De Flickering look at:
LMFlicker.
ReduceFlicker.
DeFlicker.
The source code of ...
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6
votes
Accepted
Performing DFT twice on an image. Why am I getting an inverted image?
It's a DFT property that if you apply DFT twice to input data, you get the original signal flipped (circularly). Stated mathematically for 1D case:
$$ x[n] \xrightarrow{ N-DFT } X[k] $$
$$ X[k] \...
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6
votes
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Should Edge Detection Be Applied in Spatial or in Frequency Domain?
We need to separate the concept of edge detection from the tools we use to apply the procedure.
Edges are local property of the image. Being so local means we don't analyze the image in frequency ...
- 39.1k
6
votes
Accepted
Algorithm that enlarges the image to a resolution of $2N \times 2N$ using DFT operations
I am copying my answer from Applying 2D Sinc Interpolation in the Fourier Domain (DFT / FFT).
Given a Matrix $ A \in \mathbb{R}^{m \times n} $ in order to interpolate it into a grid of size $ k \times ...
- 39.1k
5
votes
How to Calculate the Local Gradient of an Image in MATLAB
Ok,
First of all, pay attention it is a calculation per pixel using a sata from a blog.
Basically summing the Gradient norm over a block / windows.
To calculate what you submitted above do the ...
- 39.1k
5
votes
Accepted
Poisson noise and curve fitting - denoise first?
If the example images you've given are at all representative of your application, you may want to consider thinking about the problem a little differently. Instead of thinking of the image as "...
- 166
5
votes
Accepted
Which method to remove small unwanted region and fill holes
This code work fine for me. You try
...
- 166
5
votes
How to Create Image Editing Filters
The word "Filter" in Image Processing word relates to "Neighborhood" based operation on pixels.
Filters in the context of Instagram and other Image Processing applications are combination of point ...
- 39.1k
5
votes
How to Detect a Inhomogeneity Region in Image
There are many properties of inhomogeneity:
Local Variance / STD.
Local Histogram.
The Gradient Function
Histogram of the Gradient.
Mean versus the Median / Mode.
- 39.1k
5
votes
What would produce this "hamburger" corruption on images?
JPEG projects $8\times 8$ blocks of images onto $64$ 2D cosine patterns:
The one in column $1$ and row $5$, once quantized, may look like your hamburger. Luminance and chroma components may get ...
- 29.6k
5
votes
Accepted
Are There Common Values of Standard Deviation for Gaussian Noise of an Image?
You can easily have a look on the values of the STD on Image Denoising Papers:
The range of 1-15 is considered low.
The range 15-30 is considered medium.
The range 30-50 (Even above) is considered ...
- 39.1k
5
votes
Auto Detection of Rotation Angle on Arbitrary Image with Orthogonal Features
There is a similar DSP trick here, but I don't remember the details exactly.
I read about it somewhere, some while ago. It has to do with figuring out fabric pattern matches regardless of the ...
- 6,875
5
votes
Auto Detection of Rotation Angle on Arbitrary Image with Orthogonal Features
This is a go at the first suggested extension of my previous answer.
Ideal circularly symmetric band-limiting filters
We construct an orthogonal bank of four filters bandlimited to inside a circle ...
- 12.3k
5
votes
Digital Image Processing Textbook with Specific Topics
This is the list I'd recommend:
Rafael C. Gonzalez, Richard E. Woods - Digital Image Processing
Great introductory book. Well written, a lot of examples. Though it is not deep in any of the fields.
...
- 39.1k
5
votes
Accepted
Localized Gamma Correction
Gamma Correction is Pixel Wise operation.
Hence what you can do is estimate it per pixel and then average it per local area.
- 39.1k
5
votes
Recommended Order of Performing Denoising, Deblurring and Super Resolution on an Image
If your image is modeled as an image which is noisy, blurry and heavily decimated the optimal thing to do is estimate the image given that model.
The model is well defined in @Laurent Duval's ...
- 39.1k
5
votes
Accepted
2D Frequency Domain Convolution Using FFT (Convolution Theorem)
Similar to your question Applying 2D Image Convolution in Frequency Domain with Replicate Border Conditions in MATLAB the issue is what happens when you multiply in 2D in frequency domain.
So few ...
- 39.1k
5
votes
Accepted
Is the Laplacian Filter an High Pass Filter (HPF)?
There are many approximations for the Laplacian Filter (See The Hypermedia Image Processing Reference - Laplacian/Laplacian of Gaussian):
Indeed this is an High Pass Filter (HPF). Namely it will ...
- 39.1k
5
votes
Accepted
What is Label Refinement in the Context of Image Segmentation
The correct context of the refinement key word is segmentation.
Label Refinement in the context of image segmentation is a step to increase the resolution and understanding of the segmentation.
It can ...
- 39.1k
5
votes
Accepted
Locate Non Homogenous Areas in an Image
In general, the approach to take, is to have a local feature which has high value for such areas in the image.
There are many approaches to shape such a feature.
Probably the easiest one would be by ...
- 39.1k
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