[interested_observer]

Interesting experiment.....

For some time I have had a problem with people saying "you should never keep saving a file as a jpg in Photoshop, you lose quality". Being the kind of guy that will analyse most things this just didn't seem to add up. So I set out to put the record straight and experiment to find what the outcome would be after opening, saving, closing and reopening a jpg file 1000 times.

• DeadPixelPhoto: Common missconceptions and the world of JPEGs

Interesting, but still not ready to walk away from RAW.

[DSims]

The lead-in says it's about Photoshop, but then he doesn't use Photoshop!

Still, an interesting article.

[Mazhe]

This guy distorts the purposes of formats (or rather codecs), and simply use badly quality setting in place of those.

Why badly? Because when he got it precious quality 100 jpeg, he already lost much dynamic range in his image: just try to do exposure or shadow/highlight correction in jpeg.

Then, what is his point? Just use jpeg quality 100? Then you just lost what is interesting in jpeg: size. Let's take a certain 16mpx raw, export it to jpeg and png, both 8 bits:
* pef: 24 MB
* jpeg: 22 MB
* png: 29 MB
So, png is substantially bigger, but the ratio is not as good as it used to be. Compressed tiff will fall in this range. Difference with pef is insignificant for processing purposes. So clever, we have a almost non-destructive storage option that use almost as much space as raw...

So no, if you care about those things: use raw as much as you can, if you must share the picture between many softwares, use compressed tiff, and save the result with a good, yet usable, jpeg (quality 90~95).

[topace]

It doesn't have to be very difficult. The RAW is the source data. The JPEG(s) is/are the image representation of the data. Sometimes there's a more or less canonical JPEG that the camera makes directly. Don't save JPEG if you want to edit later, if for nothing else than because the effects you will want to use might benefit from data that you won't even see. Don't be afraid of JPEG for something you'll only be looking at directly.

[doghousedean]

Hi all,

Thanks for sharing my blog post.

As you can tell I'm new to blogging!

I have found some other things I will retest, like making a small change to the image on each iteration.

Any one have any other myths that need testing?

[newmikey]

Interesting thought experiment but it proves absolutely nothing at all. I posted the following reply on his blog:

"This leaves me with quite a lot of questions and also with a feeling of being intentionally misled, by YOU this time rather than by those who claim the opposite.

First of all, nobody specifically said the jpeg compression upon save would severely deteriorate the repeated saving of an unedited file. It is the sequence load-edit-save-load-edit-save-etc. that does the damage. even very small edits, like spot-removal but certainly levels, curves and sharpening will change the image sufficiently so that the jpeg compression will indeed very rapidly show quality deteriorating.

Second, you are using ImageMagick to prove your case versus Phostoshop while you have not researched what the various PS jpeg quality settings actually mean in terms of variables passed to the jpeg library or compression routine.

Third, you are not using IM's other variables that impact jpeg quality like subsampling, DCT setting, smoothing or restart markers and you have no idea how these are set standard in PS.

Fourth, why would anyone repeatedly resize an image to the size it already has? No impact on the validity of the test but you should of course the -resize 1920x1080 switch on your commandline.

Fifth, I ran your script after some changes and I come to the same conclusion as you do, but repeatedly saving a jpeg f.i. in Gimp where you make one reversible edit in a small part of the image clearly shows deterioration.

All in all, this merely goes to show that libjpeg is working fine, that ImageMagick is great when using libjpeg to save images time and time again without the image having been changed or edited in any way. That is not a real-life situation.

I appreciate the try though and always great to meet another seasoned Linux user who deals with photography! Cheers."

[doghousedean]

The idea came from the camera club I attend. It is full of old folk with little experience in computing and they often spout some random "words of wisdom". one was "you should never keep saving your file as a jpg" there was no explanation and could not explain it.

as a simple exercise I decided to test the just saving the file part. I had a feeling it would not make a difference or if it did, very little.

I have little experience with imagemagick and had to look around for syntax help.

I guess I could have optimised the resize bit but who actually cares, it would probably just notice its the right size anyway.

I will design further experiments to see what effect that has, like I posted earlier it is my first go at blogging and havn't done any writing like this in a long time.

Thanks for your comments only blogger is buggy and I am unable to see them, I did however get the notice on G+

[VoiceOfReason]

I shoot RAW+ because sometimes the image comes right out of the camera looking exactly as I want it to, but most of the time I need to do a little tweaking on the clarity, contrast, and maybe some sharpening.

[mrNewt]

I think is safe to say that as long your RAW file was modified to the extend you wanted, it is more than just OK to save a copy as a "100" JPG file.

I do similar...
I shoot in JPG and RAW - I like to have a visual just to get the idea of what I've shoot when I transfer files to my computer.
Then modify the RAW file to look as I want and save the result and overwrite the original JPG from the camera - this way I know what files I have modified from the previews and I don't need to remember which one was it.

Then, until I want a different look or a large print, I will only use the JPG generated to share, show or do small format prints from it.

Is something that for me works very well and doesn't require a lot of time...

[lister6520]

The quality loss does not occur if you save the unchanged image and retain the same compression settings for each cycle. You will however start to lose quality if for instance you even slightly change exposure, white balance or whatever and then save, reopen, change something else and so on. The main reason for this is not just the compression but also the low bit depth of just 8 bits which introduces new quantisation noise each time you alter and save. This also occurs in uncompressed jpeg. Compression introduces other issues, but as already mentioned, only if you make alterations between loading the image and saving it.