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Questions tagged [jpeg]

JPEG is a lossy image compression format, suitable for photographs and other natural images. It attempts to compress the image while retaining its visual appearance, while allowing the compressor to trade image quality for file size.

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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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Blocking effect after reconstructuring the image. Jpeg compression [closed]

The image is splitted into 8x8 blocks each of which are processed through DCT, quantization, huffman encoding/decoding, dequantization and inverse dct and used to recontruct the image. But there is a ...
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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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Is this jumbled image due to difference between Matlab and Python slicing?

When I import an image from Matlab I get the following jumbled image rather than the (224x224x3 RGB) image of a single elephant I expected I write the image from Matlab as a binary file ...
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1answer
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JPEG: In image compression why are higher frequency components divided by a larger number during quantization

Once 2D FDCT has been carried out on 8x8 blocks of the image data, the coefficients are quantized. This involves use of a quantization matrix where we simply divide each FDCT coefficient by the ...
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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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2answers
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Do JPEG formats add significant overhead?

For an extreme example, I have the following image that was a JPEG before stackexchange converted it to a PNG:- Before you perform all sorts of funky image processing tricks on it, it's just a black ...
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2answers
56 views

number of cosine waves in DCT

Why is it $N\cdot N$ a sufficient number of cosine waves equal to the size of the image or to a portion of it to describe it (or a portion of it) completely without losing information applying the DCT....
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1answer
115 views

Image not divisable by 8? (JPEG Compression)

I have learned that an image is to be divided by 8*8 blocks, and the 2D DCT is then applied to these blocks. My question is, what if the image is not divisible by 8? What should I do in this case?
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142 views

How to remove artefacts from this image?

There is some vertical banding near the tree trunks in the following image. Is there a way remove this type of artefact, preferably using Mathematica?
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88 views

What pattern maximises a JPEG file's size? [duplicate]

As I understand the JPEG algorithm, it smooths (ignores) gradual variations in colour and brightness in favour of high frequencies. This loss of information is what creates the characteristic high ...
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314 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
222 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
333 views

YCbCr to jpeg-YCbCr

Im sampling an image in YCbCr from an ov7670 camera and using jpegant library to encode a jpeg file. Whenever I do it directly using Y,Cb,Cr values from my camera, I get a pink-violet version of the ...
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174 views

How doesn't JPEG huffman table contain 256 codes?

Here are the DHT entries I got from JPEG snoop: ...
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2answers
521 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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1answer
226 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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How many 8x8 JPEGs exist with distinct DCT given a quality level?

For a given quality of image (or quality of compression), Multiple 8x8 JPEG images can have the same DCT (Discrete cosine transform) matrix, for a given quality of JPEG compression. I want to find the ...
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1answer
163 views

2D DWT computation order

In 2D the discrete wavelet transform (DWT) of an image using lifting based 5/3 filter, if I perform a row-wise operation first then perform column-wise operation then I will get 4 sub-band LL, LH and ...
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Which image filter can be applied to remove gridded pattern from corrupt jpegs?

I have around 1,400 jpegs that have been corrupted somehow and have lost the backup images. They all seem to have the same gridded pattern of lines over each (i.e. the gridding does not shift from ...
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1answer
305 views

In a JPEG file, how much is noise and how much is the image?

I have an IP webcam that generates very low light images of a plain background. The camera spits out JPEG only files. The following is one such frame... and this is with graphic equalisation ...
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2answers
1k 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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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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Why are some JPEG files of the same scene much larger than others?

I'm using a Foscam FI8910W ip camera to view a static scene under constant lighting conditions. When I pull back a frame grab, it's about 35 KB in size. I can do this over and over and it's always ...
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1answer
83 views

What would produce this “hamburger” corruption on images?

I have an image that has gone through an unknown number of jpeg and webp conversions (at least one but more likely 2+). Currently this image is a JPEG and contains corruptions in single color or mild ...
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4answers
134 views

Performing image equalisation and then Jpeg compression

I'm trying to estimate what would be the result of first performing an histogram equalisation on an image, and then compressing it using JPEG. I know that histogram equalisation increases the ...
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2answers
672 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 ...
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1answer
173 views

How to undo the quantization step in DCT?

How can I do point by point multiplication of the quantized DCT coefficients with the quantization matrix before computing the inverse DCT for each block? I want to modify the reconstruction algorithm ...
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2answers
4k 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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2answers
176 views

Usage of Digital Cosine Transform in lossy compression of images

I was reading about Digital Cosine Transform (DCT Type-I) and it's use in JPEG. I have the following doubt. My teacher offered an explanation which wasn't very convincing. What property of Digital ...
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10answers
13k 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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3answers
2k views

Retrieve pixel values from the output jpeg image

I have this jpeg image (abc.jpg) and I change some pixel values of this image and store this on hard disk, to later see the changed the pixel values. The name of the output jpeg image is say, xyz.jpg. ...
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1answer
362 views

Determining the resulting pixel value before creating a compressed JPEG image

Is it possible to determine the resulting pixel values and modify them before the compressed jpeg image is actually created? For example, I'm at the stage where I already have the quantized DCT ...
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2answers
352 views

JPEG steganography

Aside from Jsteg of Derek Upham, Outguess of Neils Provos, and F5 (improvement of F3 and F4) of Pfitzmann and Westfeld, What other methods can you use in information hiding in JPEG images? The ...
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1answer
434 views

Extremely computationally intensive image/video compression schemes which offer better compression than industry standard JPEG/H.264

I am trying to search for image/video compression schemes which offer superior compression performance (holding image quality as constant) when compared to widely adopted industry standards (i.e. JPEG/...
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543 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 ...