Compression ratio.

Q
Posted By
quickcur
Feb 8, 2005
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1132
Replies
11
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I have a tif. I save it to jpg with certain quality, say (80%). Is the compression ratio saved in the image file?

Thanks,

qq
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compression

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AT
All Things Mopar
Feb 8, 2005
I have a tif. I save it to jpg with certain quality,
say (80%). Is the compression ratio saved in the image
file?

Hi.

I’m not sure what you mean by 80%. Perhaps you mean that your file on your HD is 80% as large as the in-memory
version or perhaps you might mean that it is 20% as large (i.e. it was reduced by 80%).

Assuming you’re using PSP 7/8/9, JPEG compression off the Save As Options button is a unitless scale from 1 to 100. It is actually exponential, not linear, and not a
percentage reduction in file size.

1 will yield a file approximately half-size. I really
don’t know what 100 does, but it’ll certainly make
mincemeat out of your file!

I won’t go any further into the tall weeds and confuse you unless you have another question. But, to the question did ask, NO, AFAIK, the JPEG compression factor is NOT stored with the file.

If you really need to know what it is approximately, open the file in question and run the JPEG Optimizer: Save As> Options>Run Optimizer. Do a little experiemtation with the 1-100 factor, the Optimizer will show you a running count of the file size. When you get close to the on-disk size, you’ll have the approximate JPEG compression factor.

If there’s a direct way to do this, maybe more
knowledgeable about JPEG and PSP may answer your question.

—
ATM, aka Jerry
GR
Gordon Richardson
Feb 8, 2005
A simple question, with a very complex answer. I spent some weeks writing an article on this subject, so I won’t try to give a summary: http://www.photo.net/learn/jpeg/

wrote in message
I have a tif. I save it to jpg with certain quality, say (80%). Is the compression ratio saved in the image file?

Thanks,

qq
CF
Carl Frisk
Feb 8, 2005
I was just looking for the site a few days ago. Thanks for reposting.

—
….Carl Frisk
Anger is a brief madness.
– Horace, 20 B.C.
http://www.carlfrisk.com

"Gordon Richardson" wrote in message
A simple question, with a very complex answer. I spent some weeks writing an article on this subject, so I won’t try to give a summary: http://www.photo.net/learn/jpeg/

wrote in message
I have a tif. I save it to jpg with certain quality, say (80%). Is the compression ratio saved in the image file?

Thanks,

qq

U
Uni
Feb 8, 2005
wrote:
I have a tif. I save it to jpg with certain quality, say (80%). Is the compression ratio saved in the image file?

Nope. There are no standard compression ratios.

🙂

Uni

Thanks,

qq
L
linux4ritwik
Feb 10, 2005
Uni …
wrote:
I have a tif. I save it to jpg with certain quality, say (80%). Is the compression ratio saved in the image file?

Nope. There are no standard compression ratios.

🙂

Uni

Thanks,

qq

It really depend on the sampling rate of the uncompressed image that u start with. Generally JPEG gives 15-20% compression but if you start with an oversmapled image, you can achieve higher numbers like 80% or 100%
MD
Michael Daly
Feb 11, 2005
On 10-Feb-2005, (roshu) wrote:

you can achieve higher numbers like […] 100%

del *.*

Mike
BP
Ben Pope
Feb 11, 2005
Michael Daly wrote:
On 10-Feb-2005, (roshu) wrote:

you can achieve higher numbers like […] 100%

del *.*

One of the more lossy compression systems, that one :-p

Ben
—
I’m not just a number. To many, I’m known as a String…
U
Uni
Feb 12, 2005
roshu wrote:
Uni …

wrote:

I have a tif. I save it to jpg with certain quality, say (80%). Is the compression ratio saved in the image file?

Nope. There are no standard compression ratios.

🙂

Uni

Thanks,

qq

It really depend on the sampling rate of the uncompressed image that u start with. Generally JPEG gives 15-20% compression but if you start with an oversmapled image, you can achieve higher numbers like 80% or 100%

Compression depends on content. A more busy image will compress less than a less busy image. JPEG format was released too early. That is why the JPEG committee never embedded the compression information into the saved JPG.

Uni
CG
Christian Gollwitzer
Feb 12, 2005
Uni wrote:
Compression depends on content. A more busy image will compress less than a less busy image. JPEG format was released too early. That is why the JPEG committee never embedded the compression information into the saved JPG.

Hmm? A jpeg file (more accurately JFIF) contains the quantization tables used for the compression, because they are needed to decompress the image. These tables are the only exhausting source for the "compression quality" of the jpeg image. The construction of the qtables from the "quality value" shown to the user is arbitrary and depends on the compressor. You are right, that this "quality setting" is normally not saved, but even if it would be, it could not compared between applications.

Christian
AS
A Soberon
Feb 12, 2005
Compression depends on content. A more busy image will compress less than a less busy image. JPEG format was released too early. That is why the JPEG committee never embedded the compression information into the saved JPG.

Uni

don’t you tire of sputtering stupidities?
N
Norbtach
Feb 13, 2005
No, the compression ratio is NOT saved in the image file. If you save a picture with a certain quality, you lose information and you will never get that back
For a good explanation read this webpage.

http://www.photo.net/learn/jpeg/

Regards Robert

wrote in message
I have a tif. I save it to jpg with certain quality, say (80%). Is the compression ratio saved in the image file?

Thanks,

qq

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