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58

This is based on a misunderstanding. Loss of quality happens only during the compression that is done when an image is saved as JPEG. But it doesn't matter whether it was edited or not. So: you will (with some very specific exceptions, see comments) lose quality if you open an image in an image editor and re-save it, even if you didn't make any edits. But ...


35

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 rounding error. MCU boundaries remain are intact (8x8 blocks). Chroma subsampling is disabled. Constant DQT (same quality setting). However, rounding errors may ...


23

Absolutely not. You need to edit the file and re-save it as a JPEG in order to compound the effects of image compression. Just viewing it has no effect at all — if it did, all of the JPEGs on the web would "wear out" completely in a day or two at most.


21

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 blocks, the degradation should be minimal. However, if you're using a high level of compression, you will see further loss, because the artifacts introduced by the ...


21

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, using an optimizing compression algorithm. I don't think Google comes out and says exactly what they do, but it's probably their open source Guetzli algorithm. ...


18

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 (for a host of reasons) and may have some patent issues that might make it difficult to use in certain situations but otherwise it fits your needs. Personally ...


14

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 software can differ significantly from what another software produces when set to level 60. If you use ImageMagick as suggested by Rolazaro Azeveires, it will indeed ...


13

Uncompressed RGB files (3 values per pixel) will be larger than your raws, as the raws contain a monochrome bitmap (1 value per pixel), and usually a downscaled, aggressively compressed preview that takes a fraction of the size, 400k for Canon 10MP cameras, and 1M for Nikon D5100 (I know these numbers because I used to read them out of the raw files and ...


11

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 what to look for you may not notice the changes. Moreover, there is flexibility as to how much information is thrown away: the more you lose, the smaller the ...


9

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 directly comparing individual pixels around sharp edges or in very smooth color gradients. This is why JPEG is so popular. If it always resulted in noticeable loss ...


8

JPEG is a lossy format and it has variable quality levels which result in larger or smaller file sizes. Whenever you save a file in a lossy format, additional detail is lost, so even though you saved the finished version as a higher quality JPEG, it is still actually lower quality than the original was, despite the growth in the file size. It is still ...


8

The question here really resolves around what you mean by "quality", followed closely by needing to understand what RAW really is and how it relates to other image formats. On the first TIFF is generally not compressed in a lossy way, so artifacts weren't introduced. By that measure, quality isn't degraded in the same way it might be with JPEG (and ...


8

My solution is that I don't use Facebook to host my media files. When I post files to Facebook, I post them as links to my server. I can't use the gallery function of Facebook, but it does allow for me to have greater control over the quality of work I display through Facebook. Ultimately you get what you pay for, and Facebook is looking to use your ...


8

There are a few tricks that can help, but you'll never get the same quality out of facebook as you would from a site that allows larger files without compressing them so aggressively. Here's a link to a facebook help page that describes some of the issues. Expand the section titled "How can I make sure that my photos display in the highest possible quality?"...


8

Wouldn't it be useful to have a 24-bit RGB format (taking advantae of the camera's automatic processing modes)? Not really. Raw files are actually very space efficient, since they only store one greyscale channel, in 12 or 14 bit per pixel. A lossless 24bit format will inevitably create larger files, while dropping 4 or 6 bits of dynamic range. A 48bit ...


8

JPEG2000, and you may also want to look at OpenEXR because it is supported by video hardware.


8

You can, sort of. ImageMagicks' identify command can show a estiamte identify -verbose image.jpeg will produce (a lot of) information about the image. One of the lines will be something like: Quality: 84 If that command shows too much, and you only need the quality, you may pipe it with grep: identify -verbose image.jpeg | grep Quality (Stolen and ...


8

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 properties of the paper and ink technology limits what can be achieved. For convenience, just stick with the universally accepted JPEG and be happy with smaller file ...


7

JPEG compression can be described as having two distinct phases: first a lossy phase, then a lossless phase. Understanding the difference between them is important to this question. This isn't so much because it helps understanding what's going on, but because it helps to understand where the common mistakes come from. Lossy compression happens only when ...


7

Yes. How else could it be displayed? The screen needs to show the actual pixels, not an abstracted mathematical representation of them. Perhaps more crucially, a JPEG needs to be converted to a bitmap to be edited, which is why re-saving an image in JPEG can cause artifacts and loss of detail even if you don't change anything.


7

The JPEG format is very good for final output, filesizes are small and with the highest quality settings artifacts are pretty much invisible. It's only if you start editing a JPEG that you will see artifacts and the limited dynamic range. So it's a bad format if you plan to later edit images. If you plan to later edit images than RAW is far better than ...


7

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 recreate any image by adding together a combination of wave images with the correct brightnesses. However JPEG is a lossy compression algorithm and so it throws ...


7

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 a different encoder, you will lose the benefit. Saving with the optimizer needs to be the last step. Also worth noting: if you're starting with a JPEG and ...


7

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 to some useful dimensions. Think about how large it will be viewed and resize accordingly (keep in mind that currently a high end monitor resolution is 2560x1440)...


6

Some do — for example, most or all Pentax models and higher-end Nikons support TIFF (which, as Raheel Khan notes in a comment above, is better for metadata than PNG). So, there you go. If this is important to you, you can choose a camera which has it. However, it seems that it's not important enough to most consumers to make it something people decide on — I ...


6

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 the image (decode it) to show it, and even if you just change EXIF data, they re-encode the JPEG data instead of copying over the original. In that case, you ...


6

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 don't need to worry. My reasoning is that, like you (by the sound of things) I like to print or otherwise use a lot of my pictures as shot. But sometimes a ...


6

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 google likely has plenty of, especially as it also saves bandwdith. You can do the same - the software and various services are free or cheap. Your program / ...


6

There are photoshop plugins around like imatag or digimarc, which offer this as a professional service. The software encrypts a bit of information in a bit pattern and then hides this pattern in your image numerous times. This will work ok as long as there is enough variation in the image, which usually is true for photographies. The information is somewhat ...


6

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), without ever fully decoding the image. Therefore, its transformations are lossless: there is no image degradation at all It has a -progressive option that creates a progressive JPEG file, e.g.: ...


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