How to compress and uncompress JPEG using lossless method?
It's specified in the JPEG standard but few encoders support it. Use a lossless image format like PNG.
The Intel IPP contains a codec that supports the lossless version of the JPEG standard. Certain medical devices use this format and probably nobody else in the world.
Using the normal JPEG you can set the quality to 100% (or 1.0), but I don't think you'll ever get completely lossless compression because this is lossy by definition.
There is Lossless JPEG but it's a completely different algorithm, but I can't find any evidence of how well it's supported.
If you have any choice in the matter use png instead.
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I have PDF compressed with JBIG2. How can I recompress it to JPEG or any other compression algorithms?
I want to use open source solution like Itextsharp/PDFSharp or any other c# .net open source project.
You would need to decompress the image data, convert it from 1 bit per component to 8 bits per component, then apply JPEG compression.
But it's a bit unusual to convert monochrome images to color. This should increase the size actually. JBIG2 is pretty good for many monochrome images, why do you want to use JPEG compression on it?
I was reading about image compression, but found that the encoder for c# is lossy, is there any way to make a lossless function compressor in c#? I could only find the lossy option ( https://learn.microsoft.com/en-us/dotnet/api/system.drawing.imaging.encoderparameters?view=netframework-4.8 )
Please have a look at the Fo-Dicom library at GitHub. It is an open-source library for the use in medical imaging. They have implemented all the lossless JPEG algorithms like Jpeg Lossless, Jpeg-LS and Jpeg2000:
https://github.com/fo-dicom/fo-dicom/tree/4562544b8742c78b7b6dd49f1e47bc7952690ee5
Fo-Dicom in itself uses the Health-Efferent library (also open source), which is written in C++, but C# wrappers are implemented:
https://github.com/Efferent-Health/fo-dicom.Codecs
Use PNG to have lossless image compression in .NET.
Because PNG is by design (and also standardized by W3C and IETF) is lossless.
For more information, visit official documentation on encoding and decoding PNG using .NET:
https://learn.microsoft.com/en-us/dotnet/framework/wpf/graphics-multimedia/how-to-encode-and-decode-a-png-image
And for reference, this is the official PNG standard: https://www.rfc-editor.org/rfc/rfc2083
Update 1:
I added clarification of supported lossless image compression in .NET.
JPEG compression is by design lossy in most cases ("acceptably so") but a lossless standard does exist; you might find that some of the c# snippets on this site get you towards your goal:
https://www.graphicsmill.com/docs/gm/applying-lossless-jpeg-transforms.htm
Is there a class in C# library which does LZW compression on TIFF images. I know there is a compression scheme inviolving LZW being present, but using that doesnt decrease the file size whatsoever. Is there any thing that Im assuming wrong? Please correct me if I am.
Because LZW is loseless compression, you can compress TIFF images or any other kind of data using the same way. In C# you can use the SharpLZW library.
--EDIT (1)--
If you want to produce a TIFF file with embedded LZW compression respecting the TIFF specification look at section 13 of the specification.
--EDIT (2)--
There was a patent but it is now expired.
This is a question about TIFF and compression. I have hundreds of LZW compressed tiff images. I wonder, is it possible to convert those to CCITT T.6? Is there some API? Please help.
LZW compression can be used to compress almost any image. CCITT T.6 can compress only bilevel (black and white) images.
If your images are bilevel ones and they are compressed with LZW compression then you can recompress them using tiffcp utility (comes with LibTiff.Net library, free, source code available).
If your images are full-color ones then you will have to convert them to bilevel first. One of my answers contains sample code for such conversion.
I'm working on Steganography application. I need to hide a message inside an image file and secure it with a password, with not much difference in the file size. I am using Least Significant Bit algorithm and could do it successfully with BMP files but it does not work with JPEG, PNG or TIFF files. Does this algorithm work with these files at all? Is there a better way to achieve this? Thanks.
This heavily depends on the way the particular image format works. You'll need to dive into the internals of the format you want to use.
For JPEG, you could fiddle with the last bits of the DCT coefficients for each block.
For palette-based files (GIFs, and some PNGs), you could add extra colours to the palette that look identical to the existing ones, and encode information based on which one you use.
You'll have to distinguish between pixel-based (Bitmap) and palette-based formats (GIF) for which the steganographic technique is quite different. Also be aware that there are image formats like JPG that lose information in the compression process.
I'd also advice some general introduction to steganography including different formats.
Least Significant Bit approach does not work with JPEG and GIF images because you are using the pixel data (raw image) to store hidden information before compression. A pixel p, with data 0x123456 will probably not have this value after compression because its value depends on the compression rate and neighbour pixels. In this case we are talking about algorithms that does not only compact the image (like a ZIP, that keeps the content), but changes the color distribution, texture, and quality in order to decrease the number of bits to represent it.
However, PNG can be used just to compact the image in the same sense of ZIP file, keeping the content. Therefore, you can use the Least Significant Bit for PNG images, so that Wikipedia Steganography page shows example in this format.
As long as the image format is lossless, you can use the LSB steganography in pixels (BMP, PNG, TIFF, PPM). If it is lossy, you have to try something else, as compression and subsequent decompression cause small changes in the pixels and the message is gone. In GIF, you can embed your message into the palette. In JPEG you change the DCT coefficients, a low-level frequency representation of the image, which can be read from and saved as JPEG file losslessly.
There is an extensive research on steganography in JPEG. For introduction, I personally recommend Steganography in Digital Media: Principles, Algorithms, and Applications by Jessica Fridrich - must-read material for serious attempts in steganography. The approaches for various image formats are discussed in-depth there.
Also, LSB is inefficient and very easily detectable, you should not use that. There are better algorithms, however usually heavy on math and complex. Look for "steganography embedding distortion" and "steganography codes".