Jpeg file size


Status
Not open for further replies.

GFhana

New Member
Oct 24, 2009
31
0
0
#1
just a noob question.. I normally shoot with my GF1 12MP FINE and the file range from 5-9MBs, and resizing it to jpeg to 90% quality makes it abt 1-3mbs, just wondering, any one know why is there such a drastic difference, and will the reduced quality affects my prints? thanks!
 

ortega

Moderator
Staff member
Nov 2, 2004
23,694
10
38
Singapore, Singapore, Singapor
#2
if you don't pixel peep, then no, not much visible difference

why not try it out

open your file, save as - different name - different compression setting
do again for different settings

then print out and see
 

viix

New Member
Oct 25, 2002
525
0
0
Singapore
#3
It's the encoding algorithm..
similar colors are identified and encoded to reduce file size.. which will introduce artifact at lower quality settings.. you can see some color banding..

see this chart from wiki..

You can replicate this by saving a 12mp photo, and saving another one which is a 12mp all picture.. notice the second is only a few kb?
 

leews2001

New Member
Feb 15, 2006
255
0
0
42
3rd Rock from the Sun
flickr.com
#4
It's the encoding algorithm..
similar colors are identified and encoded to reduce file size.. which will introduce artifact at lower quality settings.. you can see some color banding..
No, JPEG does not employ perceptual color similarity detection. The banding which one observes is the result of severe quantization of 8x8 pixel blocks (DCT coefficients actually). this results in only the DC coefficient being retain for storage in the file data. hence each 8x8 block assumes the average color data with no details. this is the same effect in video coding (MPEG, H.264), in which to some extend, loop filtering (deblocking) is used to smooth out the "banding" artifacts.

additionally, if your image contains grain noise or shot noise, it is highly recommended that you save in highest (ONLY) quality setting. other wise, the same quantization process will try to remove your noise (high frequency) and result in "ringing" artifacts.

Otherwise, attempt to denoise your image first before saving in lower quality settings.
 

viix

New Member
Oct 25, 2002
525
0
0
Singapore
#5
No, JPEG does not employ perceptual color similarity detection. The banding which one observes is the result of severe quantization of 8x8 pixel blocks (DCT coefficients actually). this results in only the DC coefficient being retain for storage in the file data. hence each 8x8 block assumes the average color data with no details. this is the same effect in video coding (MPEG, H.264), in which to some extend, loop filtering (deblocking) is used to smooth out the "banding" artifacts.

additionally, if your image contains grain noise or shot noise, it is highly recommended that you save in highest (ONLY) quality setting. other wise, the same quantization process will try to remove your noise (high frequency) and result in "ringing" artifacts.

Otherwise, attempt to denoise your image first before saving in lower quality settings.
ah sweet! Now I know :thumbsup:
 

GFhana

New Member
Oct 24, 2009
31
0
0
#6
if you don't pixel peep, then no, not much visible difference

why not try it out

open your file, save as - different name - different compression setting
do again for different settings

then print out and see
yeah, even when i peep, i cant really see the difference in the image. maybe i shd print out and see the diffrence. thanks!

No, JPEG does not employ perceptual color similarity detection. The banding which one observes is the result of severe quantization of 8x8 pixel blocks (DCT coefficients actually). this results in only the DC coefficient being retain for storage in the file data. hence each 8x8 block assumes the average color data with no details. this is the same effect in video coding (MPEG, H.264), in which to some extend, loop filtering (deblocking) is used to smooth out the "banding" artifacts.

additionally, if your image contains grain noise or shot noise, it is highly recommended that you save in highest (ONLY) quality setting. other wise, the same quantization process will try to remove your noise (high frequency) and result in "ringing" artifacts.

Otherwise, attempt to denoise your image first before saving in lower quality settings.
Thats enlightening info thanks, So does process from RAW and to jpeg with 90% quality setting results in the 'ringing' as you mentioned? or just with normal jpeg 100% to jpeg 90% quality?
 

leews2001

New Member
Feb 15, 2006
255
0
0
42
3rd Rock from the Sun
flickr.com
#7
So does process from RAW and to jpeg with 90% quality setting results in the 'ringing' as you mentioned? or just with normal jpeg 100% to jpeg 90% quality?
Yes, it will. 'Ringing' artifacts is a simple phenomena in signal processing. (see http://en.wikipedia.org/wiki/Ringing_artifacts, http://www.stat.columbia.edu/~jakulin/jpeg/artifacts.htm). but in terms of visual perception, other issues comes into play such as 'visual masking'. so there is no guideline of what quality jpeg u saved in will make your picture ringing-free.

ringing begins once you save anything in jpeg. (or other lossy format) the question is how visible they are in EACH of those picture.
 

GFhana

New Member
Oct 24, 2009
31
0
0
#9
How much are you resizing? What are the original pixel dimensions, and what are the downsized dimensions?
4000x3000 just trying to change quality setting to get the size down, also wonder does everyone keep the full 100% quality pics on their machines?
 

#10
4000x3000 just trying to change quality setting to get the size down, also wonder does everyone keep the full 100% quality pics on their machines?
If you're going for prints and are using Photoshop, use "Save As" and quality level 10. There's no point in going above 10. Don't worry about the file size unless you're saving for the web. Keep as much image data as you need to get a decent print.

 

GFhana

New Member
Oct 24, 2009
31
0
0
#11
If you're going for prints and are using Photoshop, use "Save As" and quality level 10. There's no point in going above 10. Don't worry about the file size unless you're saving for the web. Keep as much image data as you need to get a decent print.

So if my photoshop cs2 only have 1 - 10? guess i will keep the maximum file size for the crucial ones then.
 

limwhow

Senior Member
Jun 9, 2009
7,048
0
0
Life revolves arOnd East Coast
#12
If you're going for prints and are using Photoshop, use "Save As" and quality level 10. There's no point in going above 10. Don't worry about the file size unless you're saving for the web. Keep as much image data as you need to get a decent print.
Interesting point, Peano.
And if we choose max quality in PS CS4 of level 12?
May I ask why is there no point in saving above the level of 10?
 

#13
Interesting point, Peano.
And if we choose max quality in PS CS4 of level 12?
May I ask why is there no point in saving above the level of 10?
You can't see any difference above 10. Professional labs (like White House Custom Color) recommend a quality level of 10. Above that, all you get is a bigger file.
 

night86mare

Deregistered
Aug 25, 2006
25,541
0
0
www.pbase.com
#14
i always save at quality 12

it's not the big a difference in file size anyways with terrabytes flying around these days

beats the hell out of saving in tiff or psd, now those are scary
 

giantcanopy

Senior Member
Feb 11, 2007
6,232
2
0
SG
#15
i always save at quality 12

it's not the big a difference in file size anyways with terrabytes flying around these days

beats the hell out of saving in tiff or psd, now those are scary
actually with terrabytes flying around, i save in psd :bsmilie:

I dun usually save at 12 unless it is for print purposes. otherwise usually ard 8 or more works for web display purposes.

leews2001, thanks for the good read

ryna
 

#17
i always save at quality 12

it's not the big a difference in file size anyways with terrabytes flying around these days

beats the hell out of saving in tiff or psd, now those are scary
I don't agree, but I do commercial work. Many a time, I was so glad I had saved .psd files with all layers intact -- and I do save all of them.

Concerning jpeg and quality levels, here is what White House Custom Color (a pro lab) says:

 

Jul 29, 2009
308
0
0
#18
Well, this is a interesting thread! Anyway, lesson of the day:
save in TIFF/PSD, print in JPG.
 

#19
Well, this is a interesting thread! Anyway, lesson of the day:
save in TIFF/PSD, print in JPG.
Unless you need a tif for some special purpose, it's sufficient to save just the psd. From that, you can always generate a copy in any format you like -- jpeg, tif, gif, png, etc.
 

night86mare

Deregistered
Aug 25, 2006
25,541
0
0
www.pbase.com
#20
I don't agree, but I do commercial work. Many a time, I was so glad I had saved .psd files with all layers intact -- and I do save all of them.

Concerning jpeg and quality levels, here is what White House Custom Color (a pro lab) says:

i keep raw files for pictures i think i want to rework.. if need be then do from scratch

well, i do have the habit of working on jpg files again, so quality 12.. maybe it cannot be seen in "print", but is there a chance that there is degradation if you save in 10 versus 12? :dunno:
 

Status
Not open for further replies.
Top Bottom