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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50 views

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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Difference between images

I am using a template matching algorithm to find a region in an image. Now there is something strange about the templates I am using. Some of them work and some others don't. And I can't find out the ...
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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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31 views

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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1answer
47 views

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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How to Generate Sensing Matrix with Variable Probabilities on Fourier Domain?

Recently, I found a good resource of Compressed Sensing applying on MRI, Michael (Miki) Lustig - Compressed Sensing MRI Resources. The variables "pdf_unif" and "pdf_vardens" store the probabilities of ...
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1answer
37 views

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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2answers
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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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1answer
33 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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4answers
236 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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2answers
60 views

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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4answers
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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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4answers
3k views

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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1answer
130 views

What are the cosine functions in JPEG's DCTII 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 DCTII. There are lots of visualizations of these waves, such as this one ...
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291 views

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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1answer
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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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2answers
162 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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1answer
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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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680 views

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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“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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1answer
416 views

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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1answer
331 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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139 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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2answers
43 views

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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112 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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1answer
557 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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1answer
35 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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2answers
35 views

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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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
499 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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1answer
184 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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1answer
425 views

compression ratio of pixels block

I am new to image compression topic and really appreciate it if someone could help me understand how compression rati works in this case. Assuming I have JPEG lossless coder that encodes the following ...
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1answer
350 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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1answer
367 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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7k views

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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2answers
1k views

Are the FFT coefficients symmetric in image processing?

On page 11 of Fundamentals of Image Processing by Ian T. Young, Jan J. Gerbrands, Lucas J. van Vliet (pdf) the results of the Fourier transform are shown (Figs 4a and 4b) and it appears to me (please ...
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Does a simple photograph contain more information than a complex painting?

I hope this question is appropriate for this site. I came across this passage in The Three Body Problem, a novel by Liu Cixin: The professor had put up two pictures: One was the famous Song ...
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198 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
2k views

Loss in converting YUV to PNG

I have a YUV 420NV12 image. I'm using ffmpeg to convert the YUV file to PNG and then back again to YUV. ...
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2answers
1k views

How does Jpeg encoding affect the final file size of 24BPP RGB and 8BPP grayscale image?

The reason I'd like to know this is because of a file size problem. I am trying to reduce an image's file size from converting it from TIFF to JPEG. A user challenge me that he notice a RGB TIFF image ...
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What are some good images to use when comparing image compression algorithms?

There was a question about images that are hard to compress. Are there images that are better suited to testing compression quality than others? Maybe an image of diagonal lines of specific colors at ...