In the DICOM spec one of the Transfer Syntaxes is 1.2.840.10008.1.2.4.70 defined as JPEG Lossless, Nonhierarchical, First- Order Prediction (Processes 14 [Selection Value 1]).
What does "JPEG Lossless, Nonhierarchical, First- Order Prediction (Processes 14 [Selection Value 1])" mean? Is this format the same as JPEG-LS? This page seems to indicate that there is some difference (JPEG-LS is listed in the bottom section).
Is is possible to read or write this format in Python? Looking over the docs for Pillow is no clear to me that the format is supported.
This post is somewhat relevant.
JPEG Lossless First Order
Identical to the main JPEG lossless, but with a constrained value for the
predictor, giving a slightly simplified algorithm, with slightly greater
speed, but slightly less compression on most images (2-5% typically)
(from medicalconnections wiki)
You may have a look at GDCM for encoding jpeg compressed dicom images.
GDCM Wiki Link
JPEG Lossless and JPEG-LS are very different implementation for image compression. JPEG lossless is defined in standard document: ITU-T T.81, ISO/IEC IS 10918-1, while JPEG-LS is defined in ITU-T T.87, ISO/IEC IS 14495-1.
JPEG-LS is a very different approach from all other JPEG-* compression family, since in its lossy form it is setup with a maximum bias from the original pixel. So you can generate a lossy JPEG-LS from an input file, where at maximum the difference in between the generated pixel and the original one, the difference is -say- 2.
Most toolkit on UNIX wont support JPEG Lossless originally because of some patent issue with the arithmetic codec:
http://en.wikipedia.org/wiki/Arithmetic_coding#US_patents
Therefore IJG (aka libjpeg) is a very limited implementation of ITU T.81 and only provides by default on UNIX distribution the lossy 8bits compression form of the standard (sequential & progressive but not hierarchical). Neither the lossy 12bits, nor the lossless 16bits is available. Technically the 12bits lossy should be possible, but since it requires a recompilation most (all?) distributions do not ship this "dual" library.
All of the above is also correct when using the new libjpeg-turbo implementation, since libjpeg-turbo is only an optimized (binary compatible) version of the original libjpeg (version 6b to be precise).
DICOM provides mechanism for supporting JPEG-LS Image Compression and DICOM standard PS 3.5 Annex A defines two different Transfer Syntaxes that reference the JPEG-LS Standard (ISO/IS-14495-1 (JPEG-LS Part 1). The Transfer Syntax with a UID of "1.2.840.10008.1.2.4.80" is lossless (bit preserving) and Transfer Syntax with a UID of "1.2.840.10008.1.2.4.81" is lossy (near-lossless) compression schemes.
I had a similar problem and I solved using #JohnnyQ hints in this way:
conda install -n myenv -c clinicalgraphics gdcm
conda install -n myenv -c anaconda pillow
Also you can use pip install ... to install gdcm and pillow.
Take a look at https://pydicom.github.io/pydicom/stable/image_data_handlers.html
Related
I built the tiff library from source including zlib and jpeg compression options. I can save with either compression type depending if I want lossless images at a higher file size, or smaller file sizes but lossy images.
The issue I have is, how do I control the JPEG quality? The program I wrote wants to be able to create both, and change the image quality when using JPEG compression. I expected there to be a tiff tag where the quality can be set, but I have yet to find that when searching. I would like to try a few different qualities between 50 and 100.
The TIFF image container must be used, so I cannot just use libjpeg directly to make JPEG images.
I search the whole TIFF source code and found the tag TIFFTAG_JPEGQUALITY that allows the setting of the JPEG quality, using an int between 0 and 100. I tested it and it does in fact change the quality.
I searched the TIFF tags website and this tag is not listed as a valid tag, but it supported natively by the latest version.
I have done a research comparing JPEG and JPEG-2000 and couldn't reach the same or better perceptual level of quality for JPEG-2000 compared to JPEG in extreme compressing levels (for web).
Although, announced as ~20+% better perceptual quality with the same size than original JPEG, with available tools to reconvert existing JPEGs or even lossless PNGs, original JPEG was still superior. JPEG-2000 managed to get arguably better results only for huge images which are not as widely used in web (Full HD and bigger).
ImageMagick, GraphicsMagick, OpenJPEG all showed identical results (I assume, due to usage of Jasper to encode JPEG-2000) and all lacked options for encoding. Using Kakadu or online/basic converters didn't help either. In current status quo, tools like imagemin with plugins, can provide much better quality JPEGs on output than JPEG-2000 when maximally compressed for web. So JPEG-2000 being useful mostly for Safari, doesn't get any point to be another format to encode since regular JPEG provides better results.
What do I do wrong and are there any other tools/tricks that have more advanced options for JPEG-2000 encoding to finally beat JPEG?
It's not just you. JPEG 2000 isn't that much better. It's difficult to encode well, and we've got more mature JPEG encoders nowadays (MozJPEG, Guetzli).
JPEG 2000 is wavelet-based, which gives it better scores in the PSNR metric. However, JPEG 2000 excels in exactly the thing PSNR metric prefers too much: blurring. It makes JPEG 2000 look great in low quality range, where the older JPEG breaks down. But it's not helpful in practice for higher-quality images. Wavelets also struggle with text and sharp edges, just like the older JPEG.
JPEG 2000 has very nice progressive loading, but Safari has stopped supporting progressive rendering at some point.
The only practical use for JPEG 2000 is delivering photographic-like images with alpha channel, because JPEG can't do that, and JPEG 2000 still wins compared to PNG.
I used cwebp to convert my jpg image to web. Now I am using dwebp to convert it back but its increasing in size from original one. Is there any way to control the file size in dwebp.
Transcoding between lossy formats tends to increase the size unless the representation of data happens to be extremely compatible between the formats, be it audio, pictures, video or other lossy data. WebP uses a 4x4 Hadamard transform, whereas JPEG uses an 8x8 Discrete Cosine Transform (DCT). Quantization, which is the main form of data loss in these formats, produces different kind of artefacts in these transformations, and transcoding cannot be optimal. Particularly, if either WebP or JPEG was saved with extremely low quality, the other format will struggle to compete with it after transcoding -- the later format will not only have to codify the image signal, but the resulting artefacts from the other format, too.
So, while there is an inherent tendency for an increase in file size in such back-and-forth conversion, the exact amount of loss happening at every stage can be controlled. Which flags and tools (including versions) are you using exactly?
I've used bigtiff library(coming from libtiff to deal with files larger than 4GB) to generate a 8GB image. It can be saved and display successfully, however, it's still to large to be transferred or shared. So I'm trying to compress it with the jpeg support from bigtiff(or libtiff), but it doesn't seem to work for me.
TIFFSetField(out,TIFFTAG_COMPRESSION,COMPRESSION_JPEG);
TIFFSetField(out,TIFFTAG_JPEGQUALITY,30);
TIFFSetField(out,TIFFTAG_JPEGCOLORMODE,JPEGCOLORMODE_RGB);
As above, I set the Jpeg quality tag to 30, and the program can be compiled correctly. However, the result turned out to be a image with jpeg quality equaling to 75 with compression ratio 0.99.
Does anyone have any idea about what's going on here or any suggestions?
Thanks,
sunhmy
There is no such thing as a JPEG quality value. Quality settings are simplifications JPEG encoders use to select quantization tables.
One encoder may use a range of 0-100.
Another might use 1-8.
You would need to find out what BigTif uses as its range of "Quality" values. It's 30 may well correspond to your 75.
You might want to play around with different values to find out.
I understand that JPEG is a lossy compression standard, and that the 'quality' factor controls the degree of compression and thus the amount of data loss.
But when the quality number is set to 100, is the resulting jpeg lossless?
As correctly answered above, using a "typical" JPEG encoder at quality 100 does not give you lossless compression. Lossless JPEG encoding exists, but it's different in nature and seldom used.
I'm just posting to say why quality 100 does not mean lossless.
In JPEG compression information is mostly lost during the DCT coefficient quantization step (8-by-8 coefficient blocks are divided by a 8-by-8 quantization table, so they become smaller --> 'more compressible'). When you set JPEG quality to 100, no real quantization takes place (because the quantization table will be all 1s, at least with standard IJG-JPEG tables), so in fact you don't lose information here..
However, there are mainly two factors leading to information loss even when no quantization takes place:
Typically, JPEG compression reduces color information (becase the human visual system is less senstitive to that than to lumimance). Therefore, even at quality 100 you may be carrying out chrominance subsampling (which means, dropping half or more Cb and Cr coefficients). When this happens, information is lost, even when no quantization happens. However, you can tell the encoder to preserve full chromimance (so called 4:4:4 color sampling).
Nevertheless, JPEG encoding implies going to the DCT domain, which causes rounding of coefficients. Rounding discards some information. This will happen regardless of all other options.
Jpeg is lossy regardless of the setting. At 100, you just get the LEAST loss possible.
It's easy enough to test. Whip up a simple .bmp, compress that to a q=100 jpeg, then re-extract back to a .bmp. Use Gimp/Photoshop to do a "difference" of the two bitmaps, and you'll see the lossiness - it'll be much less noticeable than on a q=50 or q=1 conversion, but still be present.
There is a lossless form of JPEG but it is not widely supported and you do not get it by tweaking the quality setting - it's an entirely different process.
According to wikipedia, No.
jpeg 100 has a compression ratio of 2.6:1. The compression method is usually lossy, meaning that some original image information is lost and cannot be restored, possibly affecting image quality.
There is an optional lossless mode defined in the JPEG standard; however, this mode is not widely supported in products.