35
votes
What factors cause or prevent "generational loss" when JPEGs are recompressed multiple times?
Almost all image quality losses occur the first time an image is compressed as JPEG. Regardless of how many times a JPEG is recompressed with the same settings, generational losses are limited to ...
- 26.8k
21
votes
What factors cause or prevent "generational loss" when JPEGs are recompressed multiple times?
Recompression loss is real, especially when working with higher levels of JPEG compression.
In theory, if you re-save a JPEG files with the exact same parameters and have aligned your crop to 8×8 ...
- 143k
21
votes
Accepted
Google Photos high quality backup -- how does Google achieve great compression and am I losing some data?
Well, for one thing, all photos larger than 16 megapixels are resized to 16 MP — so, for many cameras today, that's an immediate, obvious drop in resolution.
But all other photos are compressed too, ...
- 143k
18
votes
Accepted
Is there a lossy compressed file format for 16-bit dynamic range images?
It sounds like what you're looking for is JPEG2000. It has a range of options including a 16-bit lossy compression and better compression ratios than JPEG. It hasn't been as widely adopted as hoped (...
- 9,539
18
votes
Accepted
Is it possible to find out what compression ratio was used for a particular JPEG?
No, you can not and it does not make sense to do so, since there is no ubiquitous definition of the JPEG compression level. The actual result when saving a JPEG with compression level 60 in one ...
- 2,961
11
votes
Accepted
Why are JPEG images from camera huge and the same images exported from Vistaprint software 10 times smaller?
Without going into a detailed explanation of JPEG, it is (in general) a lossy format: if you save a file as JPEG and then load it again, some of the pixels will have changed. However, unless you know ...
- 1,497
10
votes
Is it possible to find out what compression ratio was used for a particular JPEG?
You can, sort of. ImageMagicks' identify command can show a estiamte
identify -verbose image.jpeg
will produce (a lot of) ...
9
votes
Why doesn't PNG show more detail than JPEG in a converted NASA image?
For photographic images and when a not too high level of compression is used, the loss of quality in the JPEG format is negligible and invisible. You'll pretty much only be able to notice it by ...
- 4,634
9
votes
Is it not ideal to save image as PNG for printing?
Yes, PNG is theoretically better than JPEG in preserving the ultimate image quality, but in practice this is the kind of exactness we don't really see, especially in print, where the physical ...
- 5,045
8
votes
Is there a lossy compressed file format for 16-bit dynamic range images?
JPEG2000, and you may also want to look at OpenEXR because it is supported by video hardware.
- 2,031
7
votes
How can I tell exactly what changed between two images?
You can use Imagemagick command line tools.
composite imagesrc1.jpg imagesrc2.jpg -compose difference diffs.jpg
will provide the absolute value of differences ...
- 71
7
votes
Accepted
Does writing EXIF tags influence jpeg quality?
There are tags that affect how the image can be interpreted by software (think about orientation), but no, the image bits should not be touched.
Now, lore says that there are (bad) editors that open ...
- 1,174
7
votes
Accepted
What are the anomalies in this picture of earth?
You're looking at JPEG artifacts. The JPEG compression scheme divides an image up into 8x8 pixel blocks and rebuilds each block using a collection of 2D waves as building blocks:
You can faithfully ...
- 119k
7
votes
Accepted
Should I resize photos before or after image optimization?
The "ImageOptim" tool pulls together a bunch of other things, and in the case of JPEG files, the relevant thing is the MozJPEG optimizing encoder. If you use this encoder and then resize and save with ...
- 143k
7
votes
Accepted
why won't my photos compress past a certain size?
I do not know at which resolution you scanned your image, but i'm willing to bet that it is way larger than needed or useful for web viewing.
The first thing you should do is resize the image down ...
- 7,003
6
votes
How does the usual jpeg 0-100 quality settings translate into Photoshop's 0-12 quality setting?
There is not a direct correspondance between standard JPEG quality 1-100 and Photoshop 0-12. The only thing they have in common is that to a bigger number usually corresponds to better quality.
...
- 686
6
votes
Compress a few small areas of an image in higher quality
You can do this with an experimental version of the jpegtran utility with the "drop" option. Get it from http://jpegclub.org/jpegtran/. Here's an example (using a ...
- 143k
6
votes
Accepted
Quality of JPEG directly from RAW+JPEG versus JPEG embedded in RAW of RAW+JPEG?
To concentrate on what you should do, I suggest you stick to the raw+jpeg. Worst case you need another card and storage is cheap. Do you actually ever get close to filling all your cards? If not, you ...
- 3,772
6
votes
Google Photos high quality backup -- how does Google achieve great compression and am I losing some data?
They are basically throwing processing power at the problem, using very compute intensive approaches that tries out various ways to compress the image within the JPG rules. Processing is something ...
- 383
6
votes
Accepted
Watermarking processing proof
There are photoshop plugins around like imatag or digimarc, which offer this as a professional service.
The software encrypts a ...
- 3,995
6
votes
Accepted
Can jpg be converted to progressive jpg without quality loss?
To convert a baseline JPEG to a progressive JPEG in a lossless manner you can use jpegtran:
jpegtran works by rearranging the compressed data (DCT coefficients), ...
- 8,588
6
votes
Image properties for social media?
None of 1-4 matter. All the major social networks (definitely including Facebook, Twitter and Instagram) re-encode any uploaded photos with their own settings, optimised for their use case (reducing ...
- 21.5k
5
votes
Accepted
Remove "random" noise
What you are seeing in your example is not random noise. It is what is referred to as compression artifacts and is what happens when an image is compressed too much to make the file size smaller.
...
- 33.3k
5
votes
Which TIFF image compression is better, LZW or ZIP?
Compression is something you can see yourself, so I'll focus on interoperability and long-term preservation.
The EU's Succeed 2014 Recommendations for metadata and data formats for online availability ...
- 161
5
votes
Quality of JPEG directly from RAW+JPEG versus JPEG embedded in RAW of RAW+JPEG?
Although the context is different, this is fundamentally a question of the difference in compression levels. ImageMagick identifies them as 81 and 95 — that's not a standard number, but it's generally ...
- 143k
5
votes
Accepted
What is difference between 8bit RGB and 16bit RGB?
The number of bits tells how many values are possible per color component. This specifies bit-depth as BPC (bits-per-component) which is what Photoshop uses. Windows on the other hand uses BPP (bits-...
- 102k
5
votes
What factors cause or prevent "generational loss" when JPEGs are recompressed multiple times?
Recompression does have a measurable effect on image quality and that effect is much more pronounced when changing compression rates.
As a quick check here as some SSIM values for operations ...
- 1,989
5
votes
Accepted
Does JPEG compression reduce actual image size?
Yes, and no :)
I think the article is speaking about the image file size (in bytes), and not the image size itself (in pixels) which is indeed unchanged.
But, to be accurate, one of the tradeoffs of ...
- 20.2k
4
votes
Which TIFF image compression is better, LZW or ZIP?
For the fastest save times you want to go with no compression. Adding compression can multiply the time required to save a TIFF by 5x on 16-bit TIFF files and by 10-15x on 8-bit TIFF files. Storage is ...
4
votes
Strange image artefacts from PS3 Eye camera
In the YUYV format, the luma channel (Y) which controls the pixels brightness has a higher resolution than the chrominance (U and V) channels, which control the hue. Each pixel has its own brightness ...
- 2,961
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