Signal Processing Stack Exchange
Signal Processing Stack Exchange

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.

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.

Examples of "lossy" compression are JPEG, which attempts to quantize the data in a manner that preserves image appearance and GIF, in which the number of colors is reduced to 256 or fewer. PNG is an example of lossless image compression, at least to the extent that up to 16 bits of data per color sample are preserved.

96 questions
49
votes
10 answers

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 must work even if the cloth is far away from the…
Nicolas Raoul
  • 595
  • 1
  • 4
  • 9
19
votes
4 answers

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 signal can be expanded to include a sparse or…
user2346
  • 291
  • 1
  • 2
12
votes
3 answers

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 Dynasty painting Along the River During the Qingming…
RSS
  • 223
  • 1
  • 7
10
votes
2 answers

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 of downloaded image is 46 Kb and the subjective…
Premnath D
  • 991
  • 2
  • 12
  • 24
8
votes
1 answer

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. I know what is YUV, but what those 420 and 411…
ZijingWu
  • 217
  • 1
  • 3
  • 8
8
votes
3 answers

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 buffer a single line, but ideally not even that. no…
Martin Thompson
  • 1,432
  • 11
  • 17
6
votes
1 answer

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: DFT decorrelates circular matrices. This is how…
Nagabhushan S N
  • 377
  • 3
  • 16
6
votes
2 answers

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 noise and not every pixel is affected by the same…
mroman
  • 161
  • 1
  • 4
6
votes
2 answers

$8 \times 8$ block matrix in JPEG image compression?

In standard JPEG format of an image, Discrete Cosine transform is used. But instead of applying the transform on whole image, we first divide the image in $8 \times 8$ block and apply transform on each of them. Thus during quantization we remove…
Virange
  • 173
  • 1
  • 6
6
votes
2 answers

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 told that mp3 does not have this problem, a…
qwalter
  • 63
  • 4
5
votes
4 answers

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 color channel separately? If so, is there any loss of…
Jorge
  • 53
  • 1
  • 4
5
votes
1 answer

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 a specific angle would be more likely to show…
gman
  • 151
  • 4
5
votes
1 answer

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] ?
Su20200
  • 111
  • 3
5
votes
2 answers

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?
Euhi
  • 53
  • 4
5
votes
1 answer

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 wavelet is more suitable for image compression…
feelfree
  • 517
  • 1
  • 4
  • 11
1
2 3 4 5 6 7