Do you save as quality 10 or 12?

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joescrivens

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I always saved as quality 12 from photoshop but I just noticed at 10 the files size goes from 15 mb in many cases down to 2mb.

Thats a serious jump. Would I be losing much to save from 12 to 10?
 
Denyerec said:
Save an image out at 12.
Save the same image out at 10.

Open both in Photoshop, copy one and place it on top of the other as a layer and set the blend mode to "Difference".

Decide if what you see bothers you more than the extra storage space :)
Click to expand...

when I set blend mode to difference all I get is a black screen :shrug:
 
joescrivens said:
but even if I save at quality 5 and overlay on quality 12 i get just a black screen. I must be doing something wrong?
Click to expand...

Not necessarily - it all depends on the JPEG subject - lots of very fine detail may get changed as the quality is altered whereas subjects with broad detail will be able to take changes better.

BTW are you saving the pics first then re-opening them?

If you don't do that then they may actually still be the same.

.
 
petersmart said:
Not necessarily - it all depends on the JPEG subject - lots of very fine detail may get changed as the quality is altered whereas subjects with broad detail will be able to take changes better.

BTW are you saving the pics first then re-opening them?

If you don't do that then they may actually still be the same.

.
Click to expand...

yes am saving first then re-openeing :)
 
joescrivens said:
but even if I save at quality 5 and overlay on quality 12 i get just a black screen. I must be doing something wrong?
Click to expand...

I have just done this with the 2 images which are on Flickr.

I simply loaded them both into my editing program - converted one to a layer then compared them both using "Difference."

The results were so small as to be almost invisible - in fact I had to merge the layers then reverse them to white to see anything at all.

Which proves what I said in that thread - that there is virtually no discernible difference between them at all.

That seems to be the case in your example.

However whether you save as 5 or 10 or 12 depends on what you are using it for.

If it's going to be edited again then I would say save it at 12 because subsequent editing may introduce changes - if only for viewing etc then 5 is fine.

.
 
You will need to stretch the histograms to see anything interesting in the differences. The way JPEG works, you'll get a close enough reproduction - even at massively different compressions.
 
You might need to apply a curve/levels to the difference output to make the differences visible to humans, as the luminosity variation will be very slight.

I personally keep everything at 12. Check out the blue channel from a compressed JPG if you're concerned as that's where the bulk of the damage is done.
 
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