Do jpg lose resolution each time downloaded?

Then when you open the file, you read 23, but you know you dropped a digit and you reconstruct a value of You made an error of 3, that's the information loss.

If you save again, gets rounded to the same number and the compression loss does not accumulate. It's more messy with JPEG because the numbers you round are not directly pixel values but same idea. Now the problem is that when photoshop reads your image, it tries to be smarter than what the JPEG standard says you should do.

JPG says: just add zero to the first two digits, that's it again I am way oversimplifying here. Photoshop thinks: JPG tells me that the first two digits are 23 and I am going to try to be super smart to guess what the true number is and make things "look better" based on secret sauce. In many cases it may guess, say, or and that's fine. But it may go overboard and guess apparently it does not even try to guess a number that actually rounds to Now when you save, it gets rounded to instead of And this kind of error apparently tends to accumulate, because the next round your may be guessed as, say, m, etc.

If I understand correctly, the loss should occur only once, until a round number is reached oversimplifying this also It means if I would try the experiment again with a program that is not Photoshop, the example I showed would not happen, at least is such an extreme manner.

Which program should you advise? Because I would love to test that. Except as you say it's simplified and it may change a few times because you do the rounding in a DCT representation, then convert back to pixel representation, which changes things a little bit.

But after a few times it shouldn't budge. I would start with free options. According to the link I posted, Gimp also tries to do something but not as aggressively as photoshop. Maybe darktable or irfan view? I should try to code it with libjpeg, which is the library most people use to save JPEG. Then at least I'd know exactly what is going on.

Lots of people still edit jpgs both my mom and mother-in-law! Back in the day, Picassa was an easy editing tool and I believe early versions saved a new jpg for every edit. My mom still misses that tool I've often wondered what the degradation would look like, thanks for posting, I think I would have given up after 10 saves, let alone 99!

Then you get the ones that ask for dpi TIF. Now, If it's going to pass a file onto my editor for extensive processing, that'll get exported at their preference because they work with the difference. JPEG works fine, I agree. And in normal cases you won't save it over and over again like my example. But it is good te see what happens if you would. It was- and still is- specifically intended to be a device-independent standardized interchange format for continuous tone photographs.

Part of this is file compression to allow for efficient network interchange. Jpeg is still overwhelmingly successful at this.

It is the world wide interchange standard and, given its ubiquity, is not going anywhere soon. It should be noted that the intent always was- and still is- that the photograph would be processed in another format and, before being sent or posted, converted to jpeg. It would seem this would be tiff or bmp formats. It should also be noted that the jpeg format is one of the recommended formats for sustainability by the Library of Congress. Again a quality of is recommended. Some photographers do process in jpeg.

They should maintain as high a quality setting as possible- if available- and limit the number of processing sessions to two or three. Those processing raw files have one session available before having to convert to another format. It would seem that tiff would be the format of choice here. Shop Now.

Home Topics Post Production. Especially for photographers who use these kind of cameras, this article could be good to read. Saving an image in JPEG format.

I always choose the highest quality, although that might be unnecessary. Nevertheless, I used this setting for my experiment. This is the starting point. After ten times saved, the quality of the file is reduced so much, you can see the artifacts appear. I already find this an unacceptable, unusable quality. Just to see what will happen when the image is saved over and over again.

After twenty times, the quality is very poor. This image can never be used, not even on social media like Facebook. The image degradation continues and this is the result after thirty times saved.

Nobody want their images to look like this. This is how an image will look after you save it fifty times. Nobody will be saving their image that many times, but is good to see how terrible a JPEG will turn out if you save it over and over again.

After seventy times, this will be the result. In addition to what has been said, you can open and then close a JPG as often as you would like without any quality loss. It only when you make a change to it requiring recompression, a lossy method, that you lose quality.

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Submit a News Tip! Reading mode: Light Dark. Login Register. Best cameras and lenses. All forums Accessories Talk Change forum. Started Feb 13, Discussions. Forum Threaded view. The GIF image format may yield better results for these latter criteria that are the more essential for greyscale photos.

This issue of JPG image degradation is true for small images with low resolution for the Web - and equally true as well as for the more demanding image criteria for large photographic print images. Either way the fact is many people eventually lose their original copy and years later all they have is some over-saved JPG's that is a a blurry image with strange square tiles all over it.

It is strongly recommended therefore that as a general rule try to be aware of the history of a given image - and whether the original image is in your hands or safely stored elsewhere. Then act accordingly in your editing procedure. Now for a little detail about the process starting with the knowledge that the compression algorythm used to produce the JPGs is based on 8x8 pixel squares.

Most of whatever you articulate is astonishingly legitimate and that makes me ponder the reason why I had not looked at this in this light before. This piece really did switch the light on for me as far as this subject goes. But at this time there is just one issue I am not too comfy with so while I try to reconcile that with the actual main idea of the position, permit me see exactly what all the rest of the readers have to say.

Nicely done. Here is a video that shows how bad a jpeg file gets after saves. Thanks for the infos though, cause i was still old-school! I suspect that the videos and demos showing significant image degradation of images after recursive recompression are the result of one of the following:.

The numbers that represent the highest level of detail are zeroed out at a level that is considered good enough quantization. Then some standard lossless compression techniques are used to finish. Recursively quantizing image data at the same quality level should throw away approximately the same level of detail at each iteration.

Eventually, equilibrium should be reached, where the input is identical to the output. The following bash commands can be used to demonstrate this equilibrium using Imagemagick on Linux:.