Questions tagged [image-compression]
image compression is a process of representing an image file or datastream using fewer bytes. compression can be "lossless", in which the original data can be recovered exactly, or it can be "lossy", in which some detail is lost for the sake of better compression.
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wavy pattern in FFT of image
I'm trying to diagnose poor image quality from a cheap camera. In addition to normal noise and blocky jpg compression, there's a pebble-like quality to them. Trying to understand this, I took the fft ...
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Calculation of Compression Ratio after DCT
I am seeking information about the compression ratios achieved at each stage of DCT-based compression processes. Specifically, I'm interested in understanding the compression ratio immediately after ...
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real time streaming image encoding options
I'm interested in streaming video real time. There is an issue of deciding how to properly encoder the images and the format they should be.
Since the data will be streamed over UDP, it needs to be ...
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Correct low pass filter after applying discrete cosine transform
I am working on the compression of a bmp image using discrete cosine transform.
First, I split the image into 4x4 blocks and then apply a DCT to each block.
I know that low frequency coefficents (the ...
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Why DCT-III is not used as forward transform for image compression applications?
DCT-II is the most widely used type for image compression. This is due to its "Energy Compaction" property. According to this property, a good enough reconstruction of a natural image can be ...
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Defining the PSNR for images in CIE-LUV or CIE-XYZ or CIE-HCL spaces
In image compression applications, we know that for an 8-bit 0 to 255 level grayscale image the PSNR (peak signal to noise ratio) can be defined through the MSE as:
$$MSE=\frac{1}{mn}{\displaystyle \...
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How to measure quality of sharpening in images
have a distorted (blurred image) and I perform several deconvolution algorithms on it to sharpen it (Richardson lucy, regularized inverse filter, tikhonov miller). And i want to measure each ...
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Robust encoding of data into visual image
I have an app which lets users download presets as ~10kB of data and share them. There's no web-service or anything, it's just posting files and stuff.
Bandwidth and storage space aren't so tight in ...
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Can JPEG XR be used for compressing binary images?
I am trying to compress some binary images i.e. images with bit depth equal to 1. For JPEG-XR encoder I used jxrlib but it is not able to compress the image. I am using specified format bmp.
Even ...
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Pros, Cons, and Applications of SVD-based Image Compression (Singular Value Decomposition)
SVD can be used for image compression:
Tim Baumann - Image Compression with Singular Value Decomposition.
Balabit Unsupervised - Image compression using singular value decomposition.
I think there ...
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Discrete cosine transform and histogram equalisation
I found an image hash library for python and this blog
In the block Getting Funky With pHash, the author writes:
Further reduce the DCT. This is the magic step. Set the 64 hash bits
to 0 or 1 ...
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Based on the eigen structure, What applications of discrete sine/cosine transformations can be found?
I am a PH.D in mathematics. I am interested in finding some applications of discrete Sine/Cosine transformations (DTTs) that are based on the eigenvectors.
I have found some results concerning ...
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Measurement of blocking artifacts in images
I want to define a threshold for maximal blocking artifacts in an image.
What is a good key value to measure blocking artifacts?
I have no reference image
non natural image
Example:
I looked into ...
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Why Is PDE Based Image Processing Not as Active as It Used to Be?
I can see from the literature that PDE-based image processing (especially inpainting) was a "hot topic" at one point. Why does it not seem to be an active area of research anymore, yet it ...
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What image processing software or technique does google's usercontent website use to serve an image in any size?
I've noticed that Stack Overflow uses lh3.googleusercontent.com to store and serve the profile images of each user. One of the features this website has is that you can easily request a resized ...
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What happens when you read and save the same JPEG image again over and over?
This question is mostly related to jpeg compression and expected results when you read and save the same jpeg file several times.
Let's say you have read an uncompressed image (originally it has never ...
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How to build the measurement matrix used for compressive sensing
I have a sparse vector $x \in \mathbb{R}^{N \times 1}$, it's real and positive, the non-zeros values are maximum $N/2$ values. It means, I have at least $N/2$ zeros values in $x$.
My question, is it ...
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jpeg compression: necessity of dividing input image into 8x8 blocks
For jpeg compression, is it necessary to divide the input image into 8x8 blocks and perform a DCT on each of the 64 blocks?
If your input image is mxn, could you just have 1 mxn DCT coefficient matrix?...
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Universal Bases (Dictionary) for Image Compression
I am a physics graduate student working on a data compression problem. I have been reading Prof. Steven L. Brunton's book on data driven science and engineering.
I am fascinated to the concept of ...
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How use of small blocks allows in description of high frequencies with less cosine terms?
I am studying mpeg compression.
Sources-:
https://homepages.inf.ed.ac.uk/rbf/CVonline/LOCAL_COPIES/AV0506/s0561282.pdf
https://fdocuments.net/document/video-compression-techniques-55849f2b11fba.html
...
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JPEG-LS: How to pick T1, T2 and T3 preset coding parameters?
I am reading ISO/IEC 14495-1 : 1999 (E). Under section C.2.4.1.1 JPEG-LS preset coding parameters, one can find the valid values ...
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custom raw compression
I'm planning to acquire between 50k and 200k image per day with a 50MPixels (or 68MPixels or 130MPixels) sensor; I'll be acquiring the raw data (10 or 12 or 14 bits) from the sensor through SLVS-EC ...
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Input data for compression algorithm
I want to implement the algorithm from the paper DhyaaAlrahman Latef Thajel1, Kadhim Mahdi Hashim1 - A New Technique for Data Compression. However in section 3.1.1, it says that it needs a binary ...
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Understanding gain of the DCT transform
I have been reading the guide from:
JPEG Huffman Coding Tutorial
I eventually reached the point where it states:
Finally, we want to convert the DCT DC value to an RGB value. Assuming
that the gain ...
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Where is truncated-SVD image compression actually used?
What are some instances of real-world sensors, cameras, filetypes, or datasets whose image compression method is (at least mostly-based on) the truncated-SVD?
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What is facebook's image compression algorithm?
For a project I'm working on (master thesis), I need to figure out what is facebook's image compression algorithm.
The goal: to be able to mimic facebook's image compression locally (using python).
...
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Sparse CWT matrix-shape data lossless compression
Is there a specialized lossless compressor for sparse matrices, i.e. large fraction (>40%) of values == 0? LZ4 worked well on 1D signals, but now whether I feed a sparse 2D or an all-zeros array ...
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Defining the SNR or PSNR for color images (3 channel RGB files)
In image compression applications, I know that for an $8$-bit $0$ to $255$ level grayscale image the PSNR (peak signal to noise ratio) can be defined as:
$$
\text{PSNR} = 10 \log_{10} \frac{\sum_{m,n} ...
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Is it possible to identify the "blank data" in a JPEG without knowing the image history?
I am pretty much a begginer in matters of Image signal and to be honest, not that much versed into mathematics. I hope my question will not sound too naive. (sorry in advance)
(Also if it has been ...
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Does decoding jpeg images uncompresses them?
I train a convolutional neural network on compressed jpeg images. I noticed that my code takes pretty much the same amount of space in memory whether I use high quality jpeg images or the same jpeg ...
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How does DCT decorrelate images?
I've read in multiple places that DCT decorrelates Toeplitz matrices and images usually have Toeplitz structure. Can you explain with an example how DCT decorrelates a Toeplitz matrix?
Example for DFT:...
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How Does Color Conversion and Downsampling work When JPEG compressing a grayscale image?
For color images I know you have to convert to YCbCr format, and then for downsampling is based on the fact that human beings see differences in Y more than differences in Cb or Cr.
How do I do these ...
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Need 600dpi JPEG file smaller than 5MB
In order to submit a document to an online website, they require the following:
Scan the US letter-size hard-copy document at 600 dpi in greyscale
Provide a JPEG, JPG, or PNG file of the scan with a ...
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Selecting a Digital Signal Processor for a Specific Image Sensor
I am working on developing a camera and I am trying to select hardware for the camera. I believe that I may need a digital signal processor to compress image data before it is transmitted to a ...
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How is downsampling and low-pass filtering done in MS-SSIM?
I am just studying the Multiscale Strutural Similarity measure for image quality and going through the original paper [1].
I think I understood the basic ides and "regular" structural similarity, but ...
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Image processing and compression
I have two questions related to this image;
Is it possible to identify any spatial domain features in the frequency domain?
My understanding: what I read around they are mostly the same as spatial ...
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About image compression vs. DCT
I have recently started reading about image processing, my knowledge in image processing is still very limited.
What I understood that DCT can help in image compression using Huffman, JPEG or MJPEG ...
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Does image size impact compression efficiency differently in different formats?
E.g., if an image is, say, 600px x 400px and the PNG format produces a smaller file size than JPG, does this hold true at any image size? If the image were 600,000px x 400,000px would the two file ...
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Why choose anything but highest compression for PNG?
I just installed LibreOffice for the first time. In the Impress
application for presentation slides, when I choose to save an image on
a slide, the file type is PNG and there is a slider for ...
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Compression algorithm to compress image relative to similar image
Is there an algorithm which can take advantage of a previous image in order to compress the next image with a level of compression / quality than otherwise?
I have an app which takes a photo of the ...
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Image compression
What happens when an image is compressed by thresholding (choosing a suitable threshold and setting the values below the threshold to zero)? Setting the values to zero doesn't mean removing them. They ...
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How to Downsample The Chrominance Components
So I am doing an image compression project for college and am trying to create a visual demonstration of how downsampling chrominance components can reduce the amount of digital information while ...
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Is there something as self-completing data transfer, like Sudoku?
I would like to know, since I am not that knowledgeable in this subject, if this idea is feasible or widely implemented:
If a data package is sent, I know parity-bytes are used to detect errors. ...
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What algorithm generates these "bucket coloring" artifacts?
Context: This is picture (taken with a smartphone*) of a copy of school test. The original answers were in black pencil and the professor made check marks in red.
However, the parts of the answer ...
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what is the difference between YUV format and HSV format?
i wonder why HSV and YUV are different formats, even though they both works similarly (based on the brightness), if not what is the difference and i have confusions with YPbPr and YCbCr , can anyone ...
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Definition of difference between compression and filtering
I'd like to explain the motivation.
It sounds like a neuroscience topic but I am after the strict Signal Processing POV.
(I don't come from a Signal Processing background).
Interested to learn ...
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Apply Principal Component Analysis (PCA) for RGB Images
I've implemented a method to compute PCA on grayscale images.
I haven't seen PCA on RGB images yet, which left me wondering if it is possible to perform it.
With RGB images, is PCA done for each ...
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What are the cosine functions in JPEG's DCT-II table?
As I understand it from this video, in a JPEG image an 8x8-pixel block is made up of weighted cosine waves, calculated using DCT-II. There are lots of visualizations of these waves, such as this one ...
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How do 2D DCT basis functions interact to produce 8x8 JPEG tiles?
This section is a bit of an intro. If you want to skip directly to where the problem is explicitly outlined, skip to the bottom of this post. Please note that I'm not hip with mathematical lingo, so ...
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Encoding YUV Color Space with Positive Numbers
I got 2 hdr rgb textures/signals. When fetched one gets bicubicly interpolated and the other bilinearly. So I was thinking I can store as YUV and store Y from each texture in the bicubic one and the ...
