Quality level when saving a re-edited jpeg from Photoshop?

[Redcrown]

I'm using the new remove tools to re-edit some old B-level jpegs in Photoshop. I noticed that when I "Save As" a re-edited jpeg, sometimes I get the Quality option window and sometimes not. I can't figure out why that is.

I always save initial jpegs at quality 10, but I use 2 different methods. Sometimes I save directly from Camera Raw. Sometimes after ACR I open in Photoshop for more editing and then save as a jpeg from there. But that difference does not seem to be the reason that I see no quality option when I re-edit.

It seems clear that when Photoshop opens a jpeg, it knows what quality level it was previously saved at. But how? I've poked around in the metadata, and I don't see an obvious flag. And why does Photoshop sometimes ask for quality level and sometimes not when saving a re-edited jpeg?

 

[Lensmate]

I'm using the new remove tools to re-edit some old B-level jpegs in Photoshop. I noticed that when I "Save As" a re-edited jpeg, sometimes I get the Quality option window and sometimes not. I can't figure out why that is.

I always save initial jpegs at quality 10, but I use 2 different methods. Sometimes I save directly from Camera Raw. Sometimes after ACR I open in Photoshop for more editing and then save as a jpeg from there. But that difference does not seem to be the reason that I see no quality option when I re-edit.

It seems clear that when Photoshop opens a jpeg, it knows what quality level it was previously saved at. But how? I've poked around in the metadata, and I don't see an obvious flag. And why does Photoshop sometimes ask for quality level and sometimes not when saving a re-edited jpeg?

If the image is saved in a different format, it may not ask for quality settings.

-M

 

[LarryRC]

I'm using the new remove tools to re-edit some old B-level jpegs in Photoshop. I noticed that when I "Save As" a re-edited jpeg, sometimes I get the Quality option window and sometimes not. I can't figure out why that is.

I always save initial jpegs at quality 10, but I use 2 different methods. Sometimes I save directly from Camera Raw. Sometimes after ACR I open in Photoshop for more editing and then save as a jpeg from there. But that difference does not seem to be the reason that I see no quality option when I re-edit.

It seems clear that when Photoshop opens a jpeg, it knows what quality level it was previously saved at. But how? I've poked around in the metadata, and I don't see an obvious flag. And why does Photoshop sometimes ask for quality level and sometimes not when saving a re-edited jpeg?

If the image is saved in a different format, it may not ask for quality settings.

-M

The OP stated hes resaving as a jpeg.

 

[JohnWheeler]

I'm using the new remove tools to re-edit some old B-level jpegs in Photoshop. I noticed that when I "Save As" a re-edited jpeg, sometimes I get the Quality option window and sometimes not. I can't figure out why that is.

I always save initial jpegs at quality 10, but I use 2 different methods. Sometimes I save directly from Camera Raw. Sometimes after ACR I open in Photoshop for more editing and then save as a jpeg from there. But that difference does not seem to be the reason that I see no quality option when I re-edit.

It seems clear that when Photoshop opens a jpeg, it knows what quality level it was previously saved at. But how? I've poked around in the metadata, and I don't see an obvious flag. And why does Photoshop sometimes ask for quality level and sometimes not when saving a re-edited jpeg?

Good question and I had to look that one up. When saving in ACR, you get the option per this image:







Choose Save Image > Save Image option and it will give you all the compression options. It defaults as 8 and you can set it to 12 and Save. If you go back and use Save Image > Save Image again it will remember the 12 level. However, if you use the options Save Image > JPEG, it will save at 8 level and resets the default back to 8 when you go back to Save Image > Save Image.

Why Photoshop does it this way, I do not know. I don't know why Photoshop does a lot of things. Note what I told you is on the recent version of Photoshop, and older ACR versions may work differently

Hope that helps

--
John Wheeler
Never give up. Never surrender. Galaxy Quest

 

[Dave_J_E]

It seems clear that when Photoshop opens a jpeg, it knows what quality level it was previously saved at. But how? I've poked around in the metadata, and I don't see an obvious flag.

There is no standard for the compression components associated with a particular Quality Level. Each software designer uses their own system. What does happen though is that certain parameters that determine the amount of compression are embedded in the jpeg file. viz

Chroma sub-sampling

Quantization table

Huffman table

These need to be known by the decoder. So i guess what happens when a jpeg is re-saved is that a choice is made whether to re--use these parameters automatically or give the user a choice of generating new ones with a new Quality setting.

Not sure what determines the distinction between the two choices.

Dave

 

[CAcreeks]

I'm using the new remove tools to re-edit some old B-level jpegs in Photoshop. I noticed that when I "Save As" a re-edited jpeg, sometimes I get the Quality option window and sometimes not. I can't figure out why that is.

I always save initial jpegs at quality 10, but I use 2 different methods. Sometimes I save directly from Camera Raw. Sometimes after ACR I open in Photoshop for more editing and then save as a jpeg from there. But that difference does not seem to be the reason that I see no quality option when I re-edit.

It seems clear that when Photoshop opens a jpeg, it knows what quality level it was previously saved at. But how? I've poked around in the metadata, and I don't see an obvious flag. And why does Photoshop sometimes ask for quality level and sometimes not when saving a re-edited jpeg?

No idea why you sometimes get Quality option and sometimes not. But if you formerly saved at quality 10, it's best to keep saving at quality 10.

Some software (not Adobe as far as I can tell) puts JPEG quality parameters near top of file. Possibly Adobe encodes them in binary that I can't see.

I have a C program that guesses the JPEG quality level and displays the chroma subsampling. Maybe Photoshop guesses? Here's what the comments say:

v1.06 1992.09.14 incorporated Phil Richards' code to guess cjpeg quality factor.
The numbers printed in the 'Approximate quality factor' line are as follows:

• Quality: an estimate of the quality factor used when cjpeg was run.
• Scaling factor (scale): mean ratio between quantization table entries
  and JPEG sample table entries, times 100.
• Variance (var): squared standard deviation of the above ratio.
  If this is larger than about 2, then the table is not a simple
  multiple of the standard's sample table, so the file was NOT
  generated by cjpeg and the quality estimate is dubious.

 

[Redcrown]

Thanks all. After some more testing I'm confident the "culprit" is Photoshop. If you use Photoshop to re-edit a jpeg that was last saved by Photoshop, then Photoshop will NOT ask for quality level (But Photoshop appears to use the quality level of input jpeg.)

If you use Photoshop to re-edit a jpeg that was last saved by anything other than Photoshop (including ACR), then Photoshop WILL ask for quality level.

I created virgin jpegs from raw using 3 programs (like Faststone). When I re-edited these in Photoshop I always got the quality option when saving. When I re-re-edited those jpegs I got no quality option because they were last saved by Photoshop. Even though the original jpeg was not made by Photoshop.

This is clearly not an issue or a bug. Just a mystery that was confusing me.