36
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 ...
- 27.1k
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 ...
- 144k
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, ...
- 144k
19
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 ...
- 3,388
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
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 ...
- 5,069
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
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 ...
- 144k
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 ...
- 7,209
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 ...
- 5,422
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), ...
- 8,763
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 ...
- 22.2k
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 ...
- 1,999
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-...
- 103k
5
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
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 ...
- 22k
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 ...
- 3,388
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
Is it not ideal to save image as PNG for printing?
Avoid PNG-8 for photo images (it is for graphics with few colors), but PNG-24 is very good choice for photo images. Better than JPG for quality, but will be a much larger file than JPG.
PNG always ...
- 12.9k
4
votes
What factors cause or prevent "generational loss" when JPEGs are recompressed multiple times?
Nothing like some experimentation. The following bash script (written on Linux, could work on OSX if you have ImageMagick):
starting with a first image (named ...
- 22k
4
votes
What are Olympus' best in-camera Jpg settings for facebook
I would recommend that you continue to use the highest resolution and the lowest compression settings. Reason for this is so that you have a high-resolution copy just in case you want to make prints. ...
- 674
4
votes
Batch Compress and Watermark Images?
The canonical utility for batch image processing is ImageMagick. Its convert command/component can change format, change compression parameters, and add text to a ...
- 22k
4
votes
How to determine which jpeg is closer to the original image and has the most information?
You can't really tell from these data. Of course, one could hope that the bigger file holds a bit more information, but it could just be the other one badly re-encoded. Utilities such as ImageMagick's ...
- 22k
4
votes
Is editing metadata of a JPEG destructive to the image?
Generally, when you do this with an image editor like Photoshop, yes, this is destructive. That's because the software doesn't keep a JPEG-encoded version of the image in memory to write back ...
- 144k
4
votes
Accepted
What are the benefits of LZW compression for TIFFs?
For me the benefits can be:
less disk space (compressed data)
less time to load (but plus time to decompress)
same for write
But I will have in mind few negative points:
compatibility, it's ...
- 12.5k
4
votes
Accepted
Capture one to export a progressive jpeg?
You ought to be able to export from Capture One in a lossless format like PNG or TIFF, then perform the JPEG compression of that lossless file once, and once only, with whatever settings you like from ...
- 306
3
votes
Is it not ideal to save image as PNG for printing?
You cannot just export a raw to TIFF, PNG or JPEG, you'll have to do some treatments, for a number of reasons. But you seem more interested in the differences between the different file formats.
I'd ...
- 3,181
3
votes
What is difference between 8bit RGB and 16bit RGB?
8bit RGB means that you have 8 bits to represent each of the colour channels (Red, Green, and Blue). 8 bits can encode 256 different states, so you can have 256 different shades of each of the three ...
- 7,209
3
votes
Is it possible to find out what compression ratio was used for a particular JPEG?
Two answers: Identify & Judge
Quick summary:
identify -format "%f: %Q\n" a.jpg b.jpg
jpegjudge a.jpg b.jpg
...
- 141
Only top scored, non community-wiki answers of a minimum length are eligible