JPEG2000 compression in an Action vs. by ‘hand’

SS
Posted By
stols_sander
May 15, 2005
Views
360
Replies
5
Status
Closed
I ran the JPEG2000 compression in an action on 16-bit TIF files with sizes 14, 56, and 224 MB. To my astonishment the resulting JPF files are about twice as large as the JPF I get when I do the compression using the "Save as…" menu item. The quality setting used was in both cases the same: 25. Using the menu item I get a reduction in file size roughly to 25%.

My question is: What is going on? Why is the file size using the Action twice as large? How do I get the normal file size at the required quality?
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Y
YrbkMgr
May 15, 2005
Just a guess but consider the following.

When one uses Save For Web in an action, and tries to optimize file size, they often become disappointed because the SFW applet will not record the target file size, rather, the percent. So the resulting files are not within the range that the user specified; rather they are at the percent reduction in quality as was calculated by the SFW applet.

A similar thing may be going on with your action in as much as what may be being recorded is either a value or a percent, rather than what you expect.

One way to test it is to take an image, perform the steps manually, then run the action on the same image. If their file sizes are the same, but the same reduction doesn’t occur with other images, then it is not recording what you expect.
HD
H.DummptySatOn
May 16, 2005
wrote:
Just a guess but consider the following.

When one uses Save For Web in an action, and tries to optimize file size, they often become disappointed because the SFW applet will not record the target file size, rather, the percent. So the resulting files are not within the range that the user specified; rather they are at the percent reduction in quality as was calculated by the SFW applet.
A similar thing may be going on with your action in as much as what may be being recorded is either a value or a percent, rather than what you expect.

One way to test it is to take an image, perform the steps manually, then run the action on the same image. If their file sizes are the same, but the same reduction doesn’t occur with other images, then it is not recording what you expect.

I did test that already: I can say that manually "Save To JPEG2000" with "Quality = 25" gives me consistenly file sizes about 25% of the original sizes for files ranging in size from 225 MB down to 14MB. It is surely by coincidence that the file size reduces to 25% when I set the Quality to 25. And just as consistently the Action, recorded with one of these files ( makes no difference whether I use small or large image files ) , results in a file size reduction to only 50%.

The only thing I can think of right now is trying to find a Quality setting that gives me the wanted file size reduction, and check afterwards whether I am satisfied with it’s quality.

And I must say that working with the "fnord" plugin is much easier and gives consistenly good results as far as quality and file size are concerned.
Cheerio, H.D.
SS
stols_sander
May 16, 2005
I did test that already: I can say that manually "Save To JPEG2000" with "Quality = 25" gives me consistenly file sizes about 25% of the original sizes for files ranging in size from 225 MB down to 14MB. It is surely by coincidence that the file size reduces to 25% when I set the Quality to 25. And just as consistently the Action, recorded with one of these files ( makes no difference whether I use small or large image files ) , results in a file size reduction to only 50%.

The only thing I can think of right now is trying to find a Quality setting that gives me the wanted file size reduction, and check afterwards whether I am satisfied with it’s quality.

And I must say that working with the "fnord" plugin is much easier and gives consistenly good results as far as quality and file size are concerned.
CC
Chris_Cox
May 18, 2005
Stols – what version of Photoshop are you using?
SS
stols_sander
May 19, 2005
Chris,
I use CS2. I have used ‘fnord’ on 5.5 and CS before with the same ease as I do now on CS2.

The Adobe PS-CS2 plugin "JPEG2000.8BI" behaves unexpectedly in my experience, especially with larger image files (>70 MB). One example:
Starting with a 89235 kB TIF, I cannot choose 22311 kB as the output size: the quality is put at ‘1’, which seems to me unacceptable. If I choose a quality of 25, the plugin says I can expect an output file size of about 18436 kB, which to me seems OK. And I get 18437, too. These two things seem to me contradictory. Smaller files (<60000 kB) behave more normally.

The other thing is that if I try to use an Action to produce a compression to about 25%, I consistently get a reduction in size to about 50% only. This is the same using the action manually or in a batch. This effect is independent of input file size.

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