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I think you should test it yourself and not just repeat what you have heard from other people.
I also have an Android phone and I'm using the Dropbox automatic upload feature on my phone to sync my pictures with Dropbox.
And I do see a difference in file size when comparing pictures pulled directly of my phone with those that have been stored in Dropbox. The file sizes of the Dropbox pictures are consistently smaller than those pulled directly of my phone. The difference isn't very large but it is definitely there.
To give you an example:
File downloaded from phone -> 5.18 MB (5.438.227 bytes)
Same file downloaded from Dropbox -> 5.04 MB (5.295.779 bytes)
So about 2.5% smaller. And this is about the reduction i see with all my other pictures too.
The resolution of the pictures hasn't changed though and even upon close inspection I can't discern any difference in image quality.
But the fact remains that picture files do get changed when they are automatically uploaded to Dropbox from an Android phone.
And I for one would like to know why and what happens to them exactly.
@Mark K. re "I think you should test it yourself and not just repeat what you have heard from other people."
I dont really care what you think, I informed I wasnt having changes, I informed that a well trained professional using iOS wasnt having any changes when asked by me to check for them (which is a lot different than just something someone hears).
That your argument accumulates to "But Im having changes so you must be wrong and test it yourself" only means that your having changes not that I must be wrong or that I should test it (again).
But if I was to follow your "advice" to test it my self, well then I DID, and I wasnt having the issue, so since the issue isnt being raised in the 1000's I would extrapolate that those that are having it are having it due to external effects rather than an application activity.
Hi Mark, thanks for taking the time to test this on Andriod and confirming that you are seeing changes to files, as you can it is challenging to engage with people relying on unknown experts!
Could you check if your photos have also got the unique ID exif tag I found? I don't have access to android device to test this myself.
Dropbox is not compressing my photos.
I've placed a full-res shot at 6016x4016 in my dropbox folder, which is then synced to the dropbox servers.
Then I went to dropbox.com and downloaded that same file and compared the two.
Same exact file size, same resolution, all the same exif data except dropbox added one extra exif line to say it was downloaded from dropbox.
I'm doing all this from my Macbook Pro and not from an iPhone or Android.
In fact, I use dropbox for work, which involves high-res PSD's, pngs, jpgs, and gifs - they are never compressed either.
The dropbox app that runs in the background on your MacBook does not compress images that are uploaded into the dropbox folder. I just downloaded an image from my dropbox account online and compared it to the file locally.
Same exact file size. Same everything except for one EXIF line added.
Here is the screenshot.
Although I have not tested this suspicion extensively, I am also of the view that DB does not compress or change res to photos on purpose. However, you may see different file sizes, depending on what device/interface you are accessing the folders/files from. Just a thought!
@S A, This is computers, not religion. if you have a file with 123,456 bytes, it will have 123,456 bytes on every system you use it, or it's not the same file. It could be a derivative of the original file, changed by a program, but it's not the same one, and it's legitimate for DropBox' users to expect their files are not changed by DB for any reason what so ever.
@Ira maybe I was not clear in my post. Here is a simple experiment to clarify what I meant: copy any file from your hard drive to a flash drive or an external hard drive and the size of the file will almost certainly be different, depending on how the devices are partitioned etc along these lines http://www.howtogeek.com/180369/why-is-there-a-big-difference-between-size-and-size-on-disk/
I am not entirely sure if this applies to DB folders/files, but I wouldn't be surprised if it did. My "belief" is that irrespective of the reported file size, the underlying res does not change, as demonstrated very clearly by @henry w. above
or it may all be the result of Lepton:
Well, the people in this thread tested not only byte numbers but also checksums like md5 and it's definitely a different file. the fact DB just released a JPG (re)compression algorithm lately suggest that their "lossless JPEG compression" is not really lossless as they claim. It's nice that it saves them about 20% of the disk space, but I stopped using this service for photos since we discovered this. in fact I only ever use it to send and receive files larger than Email allows. for all the rest I have set up a private NextCloud. I suggest the same to all the other techies in this thread.
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