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Save For Web... 1 Quality point - big jump in file size


W

Welles

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This is a 'wonder out loud' sort of question. I've noticed that when using the Save for Web... feature there is a place on the Quality slider where one point makes a disproportionately large jump in file size. It seems to me it is always at 50-51 but I'm not positive of that. Here are some results from a Save for Web... this morning.

47 = 226.7K
48 = 230.1K
49 = 236.2K
50 = 239.8K
51 = 298.2
52 = 300.5
etc.

I wonder why that sharp jump exists when files grow fairly proportionately above and below that 'break point." Needless to say I always keep an eye out for that issue when saving for web.
 
I can't be sure, but when you slide that arrow--for me, the changes come at the 30, 60 and 80 marks! Also if you notice the general settings to the left of the slider bar -- when you get those changes at those marks, the general attribute changes too -- low, 0-29; medium, 30-59; high, 60-79; maximum, 80-100. These were the settings for JPEG -- as for the other ones, I haven't figured them out yet.

As to why this happens -- I don't know, I would think this is just a compression thing! [confused]
 
I don't generally use the slider but enter the numbers manually. Perhaps that's because my entries are generally between 40 and 60, rarely above or below those figures.
 
You have to use multiple photos to test this guys -- with varyious types of visual conetnt. Every photo will yield different percentages. It's based on the amount of continuos-tone qualities in the photo/image.
 
Aha! Exactly right, Mark, and comprehensible too! Chris Cox of Adobe answered " Because at some point the JPEG coefficients change, and chrominance subsampling changes, and because some images will have details that drop out at different quality values." :B
 
Well, like my late Grandma used to say "You learn something new everyday -- that is if you are willing!" I can say that I have just learned something new! I wasn't aware of the differences in different types of pictures other than file extensions and that PNG and GIF allow you to save with bg transparencies!

Thanx for the knowledge Mark & Welles! :D
 
Welles said:
This is a 'wonder out loud' sort of question. I've noticed that when using the Save for Web... feature there is a place on the Quality slider where one point makes a disproportionately large jump in file size. It seems to me it is always at 50-51 but I'm not positive of that. Here are some results from a Save for Web... this morning.

47 = 226.7K
48 = 230.1K
49 = 236.2K
50 = 239.8K
51 = 298.2
52 = 300.5
etc.

I wonder why that sharp jump exists when files grow fairly proportionately above and below that 'break point." Needless to say I always keep an eye out for that issue when saving for web.
Click to expand...

Very interesting welles, I actuallly have used the save as for web function for years and never noticed that.
 
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