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I'm currently editing a bunch of images (JPEGs) and Photoshop keeps wanting to save them as 10/12 instead of 12/12.

Why does it constantly want to save it as 10/12 instead of 12/12? Is there an algorithm that says that 10 is enough for this picture (or all of them)?

Or a bit differently: Should I do 10/12 or 12/12? Yes, quality matters.

  • Its possible that their quality metric was 10 to begin with and PS is trying to resave same setting as they were to avoid compression on compression. – joojaa Aug 15 '15 at 12:07
  • Do you know if there is a way to check? Else I'm bloating the picture size :) – Sander Schaeffer Aug 15 '15 at 12:08
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    Adobe paid $2000 to a clever graphics engineer – Kroltan Aug 15 '15 at 14:31
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If you really are sensitive to the quality then you should avoid jpeg. You allready lost quality when the original image was saved as jpeg, nothing brings this quality back. In general you should avoid saving your documents out to jpeg unless your shipping the images off somewhere in their final form.

Its hard to say wether the quality suffers much at all, as this depends on what the original jpeg files quality was. In most cases the best quality metric is the same as you started with. Unless you cropped or rotated the image. As in theory its possible to encode each section with the same compression. Especially true if all you did was color correction or left portion of images intact.

Also theres not much point in saving much higher than original as all you get is a bigger file, for a lower compressions quality.

  • The file is taken with a DSLr camera and saved as JPEG (not used to RAW shooting (yet)). I'm doing some color- and light correction with levels and color balance and sometimes use crop. Should I save them as PNG or can I continue with JPEG? I will stuck with the saving scale Photoshop suggests (10) instead of unnecessary bloating the picture. – Sander Schaeffer Aug 15 '15 at 12:23
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    you should store your originals as PSD files with nondestructive adjustment layers for archival. You may then do jpg files from that, for convenience/distribution. – joojaa Aug 15 '15 at 12:25
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Apparently it is a relic from the days of experimentation in the Adobe labs. It is not recommended to use higher than 10 on that scale, it may actually lower the quality of the image or substantially bloat the file size. It would be a welcome change if Adobe removed that experimental extension of the scale.

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    Do you have a source for this? – BlueRaja - Danny Pflughoeft Aug 15 '15 at 17:57
  • There are various places where this might be mentioned, I am sharing a couple as seed: bit.ly/1ITSavL and bit.ly/1ITSdI5 – user45605 Aug 15 '15 at 21:16
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    That only applies to level 7; there's a big change in algorithm between 6 and 7, and 7 turns out to be less good than 6. (Or, I suppose, 6 is anomalously better than 7 because it's the best-case of a worse process rather then the worst-case of a better one.) The only problem with 12 (or 11) is file size; it's essentially incurring the loss inherent in chunking and diffing the image without offering much in the way of data compression. 12 is better than 10, but not by a large enough margin for the file size cost you pay. – Stan Rogers Aug 16 '15 at 0:25
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    No need to apologize for doing what you think is right. But, "what you think" is the operative phrase here. You will find multiple references to 11-12 range being experimental, for internal consumption, for programmers only. But, you think otherwise, be it. – user45605 Aug 16 '15 at 13:40
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    @Rafael, I have reread your "The facts" in which you refer to "data loss". I don't see a methodology where you measure the "quality loss" which is what I said. I am replying only to get the record straight, you voted down my comment with no evidence while claiming that you did. Don't confuse the terms, "data loss" and "quality loss" are not measured the same way. Larger file size is not an indication of quality, just larger file size. – user45605 Aug 17 '15 at 19:33
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1) The facts

The reason you have a higher settings than 10/12 is becouse 12/12 is a higher setting.

Here are some compression tests following my methodology explained here (In spanish, please use google translate if needed): http://otake.com.mx/Apuntes/PruebasDeCompresion2/1-CompresionJpgProceso.htm

a) Using the compression (save as) 12/12 you have a slight data loss 1/255 aprox. with a compression, compared with an uncompressed tiff (or bmp) file of 34.6%.

b) But here you have the settings as 10/12 with a "significant" data loss, with a compression of 20.4%.

2) Some notes

  • In older versions of Photoshop they used a different algorithm when you used Save As vs. Save for Web, but now the results looks the same, so they are using the same algorithm when using Save For Web with maximum quality.

  • A jpg file is recompressed everytime you re-save it as jpg. But if you save it lets say 2 times with the same settings, the data loss on the 2nd saved is not that significant as the first one.

  • Some programs can detect (or gess) the original compression level and use one simmilar acordingly.

  • Depending on the modifications, a new jpg saving could be considered as the first one, for example a resamped image.

3) Why?

I have no idea! There are sooooooooo many misconceptions on the jpg file!

Some time ago (I don't recall the source) I read a coment on a design magazine, that if someone used a maximum quality settings on a jpg file "they had no clue of what they were doing!" well, that ignorant comment made me make the initial tests on how a jpg compression behave.

The "reason" in my opinion, is just a mixture on Mercadological-Historical-GneralPublic/Use, where you "needed" to show that PhotoMightyShop could deliver a well compressed file, (back in some early dial-up web days) without any visual noticable compression artifacts.

We are still strugling with another oh my gosh prehistorical myth... the 72 dpi.

What should you use

I'm adding this part for one comment you posted on another answer.

When you edit any image from any source, it is recomended that you save your working files on a non destructive way on a non destructive format. So, if you are using Photoshop, save them as psd.

When you want to publish them again, use whatever jpg settings (or file format) you need.

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    File formats do not forbid with fiddling with data before you export it. Just as long as standard readers produce output your ok. This means that new ways and new innovations can be made. As for the range, i dont think jpeg defines what the settings have to be. But yes theres so much misconception around anything technical. People update their info and assumptions in times that are measured in generations. – joojaa Aug 16 '15 at 12:56
  • Here is a quality comparison of JPEG quality levels, this article also appeared on PetaPixel.com. keptlight.com/does-size-matter – user45605 Aug 18 '15 at 16:36

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