Questions tagged [image-compression]

Image compression comprise methods with the goal to reduce the size of an image by either removing redundant or less important information (or a combination of the two).

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24
votes
6answers
39k views

What are jpeg artifacts and what can be done about them?

I know JPEG is a "lossy" compression algorithm that discards information in order to save space. What is the visual impact of this? I've heard of "JPEG artifacts". What do these look like? Are there ...
31
votes
4answers
6k views

What factors cause or prevent “generational loss” when JPEGs are recompressed multiple times?

For years, I've believed that recompressing JPEG files multiple times would gradually degrade its quality until they are an unrecognizable mess, the way making photocopies of photocopies does. This ...
8
votes
3answers
4k views

Does JPEG-to-JPEG export Lightroom reapply compression?

I want to crop a JPEG file in Lightroom and export that cropped file to another JPEG so that I can e-mail it. The exported JPEG should have the same quality as the original. I don't have the RAW file ...
58
votes
1answer
18k views

Are “Windows Photo Viewer” rotations lossless?

Can I rotate lossily compressed photos that I view in Windows Photo Viewer without worrying about losing even more information to compression?
47
votes
6answers
173k views

What quality to choose when converting to JPG?

When you export a picture to JPG you can normally choose its quality in a 1-100 scale. I like to keep a good quality but it wouldn't make sense to keep a JPG that will be almost as big as the original ...
19
votes
3answers
9k views

Why does JPEG quality go up to twelve?

Wwhy does the JPEG quality option in Adobe products go up to twelve? Here's the option in the Save dialog of PS: Thats a whole new definition of it goes up to eleven.
59
votes
7answers
21k views

Why don't most cameras support PNG format?

I prefer PNG format to JPG, because JPG uses lossy compression. When I capture a screen in my PC or scan a picture or document in my scanner, I always save them as PNG format. If a camera could ...
7
votes
10answers
165k views

How to reduce the file size of my photos (to under 15 MB)?

I don't have a "Pro" account on Flickr, just the free one, so my photo uploads are capped to 15 megabytes/file. After post-processing, my photos end up being too large to be uploaded to Flickr. I do ...
25
votes
12answers
39k views

Does simply opening and closing a JPEG file decrease image quality?

I've had quite a few photography classes, read many photography books, and screened many forums. And I can't find a consistent answer to this question. One "camp" says there is a loss of image quality ...
9
votes
2answers
522 views

Is there a middle ground format between RAW and JPG?

JPG files use 8 bits per color per pixel (I've never heard of any camera that uses the alleged 12-bit-per-color-per-pixel extension) and is a compact way of storing images. RAW files are huge but ...
4
votes
5answers
2k views

How can I resize more than 2GB of travel photography with no quality compromise?

I have more then two gigabytes of travel photography. Each image takes up than 4 to 5 megabytes. I have to send them to some one. How can I resize all images while retaining high image quality?
3
votes
4answers
25k views

What image quality is lost when re-saving a JPEG image in MS Paint?

Has anyone ever noticed that if you open a image in mspaint (.jpg, .jpeg) and then just save it, the image size is reduced by many folds. I use this method to reduce the file size. However, I am not ...
3
votes
4answers
18k views

Does converting RAW files to TIFF lose image quality?

Before I found out about Camera Raw, I used to convert my photos from RAW to TIFF, using the XNVIEW convertor, downloaded from the Internet. My question is whether I lost image quality or anything ...
1
vote
5answers
2k views

How does optimizer software reduce file size without reducing resolution?

There are numerous applications for reducing filesize. Most of them reduce resolution (e.g. from 300dpi to 72dpi) or reduce height and width. I tried http://www.imageoptimizer.net/ Surprisingly, when ...
31
votes
6answers
37k views

How can I tell exactly what changed between two images?

For example, for a recent conversation about JPEG compression I wanted to compare pixel for pixel what changed between two JPEGs (one with compression level 100, and one with compression level 95). ...
22
votes
3answers
29k views

Which TIFF image compression is better, LZW or ZIP?

Which image compression is better, LZW or ZIP? I am using Lightroom to export images.
17
votes
3answers
10k views

Does Flickr recompress JPEGs after upload?

Does Flickr recompress JPEGs after upload? I know that if you upload a TIFF, for example, Flickr converts it to JPEG. But do they also compress incoming JPEGs? I've read some complaints about the ...
13
votes
4answers
19k views

How to avoid jpeg compression artefacts when saving photos in web resolution?

When I save a web-resolution image (for example, 1920×1024px), flat areas tints often have damaged shades of color. I'm saving in Photoshop CS4 with quality 2 in standard mode, because I need the ...
22
votes
2answers
6k views

Google Photos high quality backup — how does Google achieve great compression and am I losing some data?

I'm sure that many of us have used Google photos high quality backup which allows us to store photos online without fees. Recently, I thought of testing just how high quality the uploads really were ...
15
votes
3answers
5k views

Is there a lossy compressed file format for 16-bit dynamic range images?

I'd like to aggressively compress some scientific 16-bit grayscale image files, but without reducing the dynamic range. Is such a thing possible? I understand that JPEG format uses lossy, and ...
30
votes
5answers
4k views

Why don't cameras support JPEG 2000 format?

The original JPEG format was updated in 2000 to provide a variety of features including less artifacts, better compression and lossless compression. Why haven't cameras updated to use this new format?...
10
votes
4answers
32k views

Why are two pictures that are the same dimensions/dpi such different file sizes?

I am working on a project where two my images must be AS SMALL AS POSSIBLE. I have scaled two images to the same dimensions/dpi and I've checked the color profile in Photoshop CS6 and they both look ...
3
votes
3answers
8k views

Why does simply saving a JPEG at 100% quality in Photoshop increase filesize?

If I take a picture taken with my EOS 60D, put it into Photoshop, edit it as I wish and save it as JPEG with maximum quality, the file goes from 5 to 12 mb in size. Obviously if I didn't increase the ...
0
votes
4answers
201 views

Lossy archival compression for 16-bit TIF images

I sometimes use the Nik collection to process my photos, and because this runs on TIFF images, I end up with demosaiced files eating up more disk space than they're worth. I want to batch convert ...