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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3answers
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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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How doesn't JPEG huffman table contain 256 codes?

Here are the DHT entries I got from JPEG snoop: ...
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1answer
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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
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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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1answer
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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 ...
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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 ...
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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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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
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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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1answer
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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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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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2answers
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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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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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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. ...
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1answer
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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 ...
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2answers
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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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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 ...
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1answer
514 views

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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1answer
112 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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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 "...
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1answer
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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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2answers
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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 ...
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1answer
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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 ...
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2answers
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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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2answers
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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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0answers
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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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1answer
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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. ...
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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 ...
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2answers
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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 ...
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0answers
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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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2answers
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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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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 ...
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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 ...
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1answer
290 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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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
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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10answers
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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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3answers
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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 ...
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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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