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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49
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10answers
16k views

What is the least JPG-compressible pattern? (camera shooting piece of cloth, scale/angle/lighting may vary)

I am trying to design a cloth that, from the point of view of a camera, is very difficult to compress with JPG, resulting in big-size files (or leading to low image quality if file size is fixed). It ...
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4answers
906 views

Applicability of compressed sensing / compressive sensing

From what I have heard, compressed sensing can only be utilized for a sparse signal. Is this correct? If that is the case, how can a sparse signal be distinguished from any bandlimited signal? Every ...
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3answers
1k views

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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2answers
5k views

What is the Compression Algorithm used by Facebook?

I would like to know what is the Compression Algorithm used by Facebook for compressing the images? I uploaded a image of size 242 Kb and I downloaded the same image from my Facebook album. The size ...
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3answers
2k views

Simple, streaming, lossless image compression

Does anyone know of any image compression techniques with the following characteristics: lossless streaming - I want to compress on the fly, pixel-by-pixel. low-memory overhead - I can afford to ...
7
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1answer
16k views

What does the 420 means in YUV420?

I'm not sure if is the correct location for ask this question. If not please info me the correct StackExchange site. As this wikipedia page show, there is one YUV format of image as YUV420 and YUV411. ...
6
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2answers
1k views

Difference between jpg compression and mp3 compression

My understanding of jpg compression is that, if done repeatedly, any image will eventually be reduced to a single flat color, due to the way it deals with neighboring pixels. However, years ago I was ...
6
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2answers
5k views

8*8 block matrix in JPEG image compression?

In standard JPEG format of a image, Discrete Cosine transform is used. But instead of applying the transform on whole image, we first divide the image in 8x8 block and apply transform on each of them. ...
6
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1answer
338 views

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:...
6
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2answers
3k views

Random Noise Removal In Images

I'm trying to remove random noise from an image. The noise is arbitrarily random so it must not necessarily follow a certain distribution (Not every pixel has the same chance of being affected by ...
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1answer
1k views

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 ...
5
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1answer
301 views

Does every 8 by 8 DCT matrix have a valid (in range) IDCT?

For a given quantization level of JPEG compression, are all possible DCT matrices have valid IDCTs. By valid, I mean matrices whose elements are in the range [0,255] ?
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5answers
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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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4answers
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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 ...
4
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2answers
2k views

JPEG DCT padding

Since the JPEG DCT block used is 8x8, how does the method deal with images with dimensions that are not multiples of 8? What kind of padding does it use? How are the 8x8 blocks of the image chosen?
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1answer
3k 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. ...
3
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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 ...
3
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1answer
1k views

Why Wavelet based Transform Is More Suitable for Image Compression Compared to DCT?

Everyone knows that JPEG2000 can obtain much better compression result than JPEG. The fundamental transform behind JPEG2000 is wavelet while the basic transform in JPEG is DCT. So my question is why ...
3
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1answer
65 views

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 ...
3
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1answer
714 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 '...
3
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1answer
776 views
3
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1answer
1k views

What is the Difference between Texture and Image?

I am beginner in the image processing I want to know what is difference between Texture and Image? or whether they are same? can anyone explain it. Also,if i want to do texture segmentation,can i ...
2
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2answers
131 views

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 ...
2
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2answers
736 views

Compare between JPEG and JPEG2000

JPEG image compression is Fourier based DCT while modern image compression technique like JPEG2000 is based on more multi-scale technique like Wavelets.I want to know how Fourier and Wavelets are ...
2
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4answers
460 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 ...
2
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2answers
785 views

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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2answers
2k 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 ...
2
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2answers
188 views

How does using DCT help in image compression

I once learnt that the Huffman Encoding is used to rid of redundant information, thus reducing file size. I am not sure how using a DCT, or FFT on an image can help in reducing file size. It does not ...
2
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1answer
184 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 ...
2
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2answers
49 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 ...
2
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1answer
675 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 ...
2
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1answer
525 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 ...
2
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2answers
205 views

Fast method to decompress huffman and arithmetic encoded data

By nature, when decompressing huffman (and I assume also Arithmetic encoded data) we have to read it in bit by bit and then see how it traverses a huffman code tree that has the actual symbol value at ...
2
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1answer
567 views

What does it mean for an image to be "Markovian"?

I've been following the recent lectures on Coursera for image processing. In the lecture on the use of the discrete cosine transform (DCT) for image compression, he says that for images that are "...
2
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2answers
272 views

In image compression using transforms, how to deal with the transformed coefficients as they are not integers?

I am new to the field of image compression. While going through various texts, I read about how transforming the image to another domain using, for example, the wavelet transform, or the DCT, makes it ...
2
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1answer
62 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 ...
2
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1answer
673 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 ...
2
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1answer
134 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 ...
2
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0answers
371 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 ...
2
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0answers
186 views

How does Golomb-Rice Coding work?

I've read the explanation in http://urchin.earth.li/~twic/Golomb-Rice_Coding.html and http://en.wikipedia.org/wiki/Golomb_coding , however, I still not get the intuition why it is efficient and when ...
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4answers
808 views

Skip corrupt part of jpeg

Is it possible to read a JPEG file and skip parts that are corrupt? I have three corrupt JPEG files and I can detect the first corrupt block, but can I skip it and continue with the next block? I ...
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2answers
78 views

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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3answers
144 views

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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2answers
785 views

Confusion about shannon's entropy of the grayscale image after lossy compression

I have a .pgm format 480 * 640 gray scale image named 'columns.pgm'. Using PCA (principal component analysis), by preserving 40 principal components I compressed original image with 1218 KB to 301 KB ...
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3answers
377 views

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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1answer
39 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
67 views

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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1answer
784 views

PNG IDAT specification

I'm going over the W3 PNG specification (creating a PNG library from scratch) and I've finally found how to create a green 1x1 image. Now I'm trying to create a bigger image of mixed Red, Green and ...
1
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1answer
142 views

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 ...
1
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1answer
472 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} ...