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 are some techniques to recover an original image from three different compressed versions?

This question is theoretical. Let's say you have three different highly compressed images of a same source image, each compressed with a different algorithm and thus "lossy" in different ways. What ...
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571 views

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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54 views

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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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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233 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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48 views

What base image size to choose to assist easier downsizing?

Android applications need image at different resolutions to support different screen densities and pixel size. I am planning to provide only one image with high pixel size and let the underlying ...
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1k views

pixels in the same image are correlated but how can I visualize it?

I am new in image processing.I know that pixels in the same image are correlated with each other but I don't know how can I draw the relationship b/w these pixels in the form of graph?.
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Why don't DSLR cameras default to png instead of jpeg? [closed]

I'm working with a new DSLR camera for a Computer Vision application and I noticed most of them default to saving in the lossy JPEG format. Initially, this caused some problems in my application and I ...
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404 views

How to apply dictionary learning to several images?

I'm implementing a dictionary learning algorithm for doing sparse coding on images and I have a problem how to learn a dictionary corresponding to several iamges. Let’s say X is the data matrix. If I ...
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26 views

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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143 views

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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"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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39 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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462 views

Compression ratio for 4x4 block

Say I have the following 4x4 block: [ 120 121 125 119 120 120 118 117 122 121 117 118 122 122 120 120] If this block is intra coded the ...
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80 views

Image Compression (JPEG) - Show the Effect of Number of Coefficients on Quality

write an m-file that will take the"cameraman" and produce a image quality or difference matrix for spectral selection method.The image properties are a sfollowings: For spectral selection: image1:DC ...
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116 views

Sparsity limits of compressed sensing - is this right?

Compressed sensing (CS) guarantees exact object recovery (or with high probability) given a) sufficient measurements are taken in a sparse basis which is b) incoherent vis-a-vis a given object ...
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546 views

Confirming what a compression ratio is

I have looked at various sources, but still have not been able to answer the question: what is compression ratio? I have come to the understanding that this is the definitive answer: compression ...
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50 views

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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Origin of brightness artifacts in intensity resolution compressed images

when compressing this image (It corresponds to Fig2.20 from the book Digital Image Processing by Gonzalez and Woods and the original .tif document can be downloaded through this link By reducing ...
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1answer
117 views

How does a wavelet help in image compression?

I understand how the discrete cosine transform is used in image compression in standards like JPEG. However, the concept of wavelets is a mystery to me. I do know that wavelets are functions that have ...
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2k views

Image compression using SVD in MATLAB

I have to compress an image using SVD. I did a few things, but all of them produced a black & white image. However, the output must be RGB. How can I compress an image without changing its ...
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1answer
67 views

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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Which channel coding technique is suitable for wireless SPIHT compressed image: Reed-Solomon or convolutional code?

I want to transmit a SPIHT-based (Set Partitioning In Hierarchical Trees) image compressed image over a wireless fading channel, which will be suitable as channel coding technique: Reed-Solomon or ...
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298 views

Selective image compression?

Forgive me if this is the wrong site for this question. Here's my problem: I am creating a game where players have to search for a hidden detail within the overall image. I downloaded an 11MB ...
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82 views

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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1answer
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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 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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393 views

How to predict next image in a sequence, or predict the deblurring of an image?

I have 3 versions of an image at lower resolutions - 480p, 720p, and 1080p. Is it possible to use those 3 images to predict the next highest resolution image (the 4k image)? My first guess was that ...
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Bit plane slicing in python

I recently came across a technique called bit-plane slicing for image compression in a book "Digital image processing" by gonzalez and woods . They just presented the theory and i wanted to ...
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131 views

What is this kind of distortion called?

Today while watching a movie I noticed the following distortion: Note. The red ring is me painting over to show the area of interest. There are certain areas in which I can see non-smooth shades of ...
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106 views

How to choose basis functions that contribute most efficiently per term to an approximation of an image f(x,y)?

GOAL: I would like to approximate some positive, scalar function, $f(x,y) > 0$, on a 2D field of finite size i.e. $x=[a,b],y=[c,d]$ OBSTACLE: I am familiar with the set of basis functions used ...
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291 views

Lossless algorithm for hyperspectral imaging

I am looking for Lossless compression algorithm for hyperspectral imaging. The only one that I found was LPVQ. Do you know other algorithms? I am looking for pseudocode or matlab code. Thanks
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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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APT Satellite Image False Coloration?

I'm working in MATLAB to try to take pristine APT satellite images (two greyscale images of the earth taken at different wavelengths) and turn them into one false-color image. I also have a second ...
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500 views

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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23 views

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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121 views

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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217 views

How doesn't JPEG huffman table contain 256 codes?

Here are the DHT entries I got from JPEG snoop: ...
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1answer
173 views

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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206 views

Quadtree decomposition of Discrete Wavelet Transform using bio4.4/CDF wavelet

My problem is pretty basic but fundamental. It relates to the way discrete wavelet transform behaves for biorothognal 4.4 or CDF wavelets. When using most wavelets (e.g., CDF 9/7 or bio4.4 or ...

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