15
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 \...
- 5,960
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, ...
- 31.3k
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 ...
- 13.2k
9
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 ...
- 50.3k
8
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 ...
- 50.3k
8
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 ...
- 50.3k
8
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 ...
- 50.3k
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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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 ...
- 50.3k
7
votes
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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 ...
- 50.3k
7
votes
Accepted
Why Is PDE Based Image Processing Not as Active as It Used to Be?
PDE for image processing had its glory days when we didn't have a good model for images.
Back in those days, PDE's were the best models as they were mathematically understandable and in many times ...
- 50.3k
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
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] \...
- 27.6k
6
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 ...
- 50.3k
6
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.
...
- 50.3k
6
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.
- 50.3k
6
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 ...
- 50.3k
6
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 ...
- 50.3k
6
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 ...
- 50.3k
6
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 ...
- 50.3k
6
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 ...
- 50.3k
6
votes
How to Remove Temporal and Fixed Pattern Noise and Apply Tone Mapping?
Noise Measurement
You may use the MAD (Median of Absolute Deviation, See Relation to the Standard Deviation) Trick for noise estimation. Basically applying an High Pass Filter on the image and scale ...
- 50.3k
6
votes
Accepted
Filter Artifacts from Periodic Filtering
What you see is indeed by either using filtration on the frequency domain which uses periodic boundary condition or by using is explicitly.
A better choice would be the ...
- 50.3k
6
votes
Accepted
What Measure to Compare the Color Depth (Distribution of Colors) of Images
One measure you may use is the Entropy (Information Theory) of the data.
Its definition is given by:
$$ H \left( X \right) := - \sum_{x \in \mathcal{X}} p \left( x \right) \log p \left( x \right) = \...
- 50.3k
6
votes
Accepted
Edge / Pixel Type (Homogenous, Edge, Texture) Classification as Part of an Image Denoising Procedure
Even not anymore modern methods like the Bilateral Filter, Guided Filter and Non Local Means do not filter the image in a uniform manner.
They all apply some kind weighing based on the properties of ...
- 50.3k
5
votes
Image Compression Using the SVD in MATLAB
Let's do that in a hands on approach.
We'll follow this steps:
Apply the SVD to the Image Blocks.
When you compress with SVD you should compress blocks of the image.
The reason is simple, images are ...
- 50.3k
5
votes
Noise Removal from an Image Using OpenCV (Comparison to Neat Image)
NeatImage probably uses Wavelets based Noise Reduction.
You can look for methods based on that.
Today you need methods which are "Edge Aware", namely they smooth yet keep edges in tact.
Have ...
- 50.3k
5
votes
Accepted
Amplitude of an Image
I don't see the question here.
But you're right.
On the DFT map of the image, the magnitude / amplitude, etc. are powers of the length of the vector of the complex number.
On more useful ...
- 50.3k
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 ...
- 31.3k
5
votes
Removing Noise from Dental Radiography
As far as I understood, by image derivation you mean extracting edges. I would recommend to filter the image by a relatively large Gaussian filter. If computational cost of image derivation is ...
- 1,996
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