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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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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13 votes
4 answers
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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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When Golomb Coding is used for image compression in Image Processing?

I was reading about the Golomb coding related to image compression in Image Processing field. The algorithm, takes a nonnegative number and turns into some binary string. It made me wonder, when this ...
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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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Compressing images with masked areas

Im looking for the best way to compress and store images for a ML project, where only part of the image is useful. The best example is a picture frame, where we want to delete the painting, but keep ...
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How to find the number of vectors to sample in Compressed Sensing?

When comparing my MATLAB code to a previously written one, I come across the following formula for the number of vectors to sample: ...
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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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3 answers
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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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2 votes
1 answer
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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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1 answer
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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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2 answers
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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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2 votes
2 answers
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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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1 answer
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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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2 votes
4 answers
763 views

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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1 vote
2 answers
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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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2 answers
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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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6 votes
4 answers
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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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2 votes
0 answers
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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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5 votes
1 answer
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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 ...
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What are the differences between Gaussian down-sampling and bicubic down-sampling in Matlab? Which is more accurate for simulating low resolution?

I see in some of the technical papers, good practice for downsampling is to first pass the image through a Gaussian Filter and then take sampling to avoid problems like aliasing and so on. However, ...
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1 vote
2 answers
263 views

JPEG compression steps after quantization

I have a 3-channel (for colours) a png image that I opened and I splitted the image into 8x8 blocks I applied all of the blocks discrete cosine transform And then applied quantization I stored the ...
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1 answer
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Coherence Calculation in Sparse Sensing

i have an image I of size 32*32. I perform the DCT of this image using the matlab function DCT2(I). I get a sparse representation of my image which is again a 32*32 image. I construct a circulant ...
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How to determine a quantization table for image compression with DCT?

The quantization table is given on the JPEG Wiki page. How was this table derived? I'm currently doing a project where I have to come up with custom quantization table for an image, but I don't know ...
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1 vote
0 answers
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"Image Processing" [closed]

I'm an Italian student. I'm studying Gnu Radio and I would like to upload a photo, can I upload it with "file image source" or other blocks? I need to make FFT of an a image. -> image 2D Thank you ...
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2 votes
1 answer
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Facing problem in plotting histogram of DCT coefficient of an image

In digital image forensic, it is assumed that the histogram of DCT coefficients of the un-compressed natural image has the smooth histogram. However, the histogram of DCT coefficients of the ...
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5 votes
1 answer
901 views

How Does Mean Centering Affect the Result of Using SVD to Compress Images?

I have been learning about using the Singular Value Decomposition to find low rank approximations to matrices. I had an image which I converted to a matrix. I regarded each row of the matrix as a '...
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-1 votes
1 answer
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How to Approximate the File Size Ratio of Two JPEG-LS Compressed Images? [closed]

For instance, a high-resolution image (25MP) and a low-resolution image (4MP) of the same scene. When compressing them both with ...
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4 votes
2 answers
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How Can JPEG Be Used to Realize a Transfer Application with a Fixed Bit Rate? [closed]

For simplicity, assume a fixed bandwidth (5MB/s) and that each second an image with 12MP is generated. The quality of the image ...
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0 answers
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Reconstructing image from the dwt coefficients

I am trying to compress and reconstruct an image but facing problems with the data type of the compressed image pixel values which are of float64 and therefore, when I am trying to retrieve the pixel ...
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2 votes
1 answer
755 views

`SSIM(YUV)` vs. `SSIM(Y)`: Values Are Very Different

I'm seeing some weird results when trying to compare image qualities in a few different color spaces. Have a look at my graph: I want to compare with another publication, which reported PSNR(YUV) and ...
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1 vote
1 answer
41 views

Need a 2 parameter ranking system for image compression

I'm working on a project in which specific bit planes of an image are extracted and compressed. This process is repeated for every combination of bit planes possible.For an image, I have calculated ...
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