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JPEG Compression Question

 
 
Les
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      08-23-2005
I shoot in high resolution JPEG mode with my camera. I download the
files to my computer for archiving and editing. I save each picture as
a TIF for editing. After I complete my editing, I save the edited TIF
as a high quality JPEG.
My question is this: Is the edited JPEG the still same quality as the
original JPEG downloaded from the camera?
Thanks for any info you can provide.

 
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Thomas T. Veldhouse
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      08-23-2005
Les <(E-Mail Removed)> wrote:
> I shoot in high resolution JPEG mode with my camera. I download the
> files to my computer for archiving and editing. I save each picture as
> a TIF for editing. After I complete my editing, I save the edited TIF
> as a high quality JPEG.
> My question is this: Is the edited JPEG the still same quality as the
> original JPEG downloaded from the camera?
> Thanks for any info you can provide.
>


There are always small errors created when you save an image as JPEG, as
it is a lossy compression scheme .. which means you have lost data.
Now, when you convert to TIFF, you have lost nothing over the original
JPEG, so the original loss is simply maintained. You then save your
JPEG from the modified TIFF and you again apply a lossy algorithm and
get more loss. So, the answer is the new JPEG is of lower quality [as
far as dataloss is concerned] than the original. Having said that, if
you never modify your new JPEG images and always work from your original
TIFF, your loss can be considered neglible.

--
Thomas T. Veldhouse
Key Fingerprint: 2DB9 813F F510 82C2 E1AE 34D0 D69D 1EDC D5EC AED1
Spammers please contact me at http://www.velocityreviews.com/forums/(E-Mail Removed).

 
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MarkČ
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      08-23-2005

"Les" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed) ups.com...
>I shoot in high resolution JPEG mode with my camera. I download the
> files to my computer for archiving and editing. I save each picture as
> a TIF for editing. After I complete my editing, I save the edited TIF
> as a high quality JPEG.
> My question is this: Is the edited JPEG the still same quality as the
> original JPEG downloaded from the camera?
> Thanks for any info you can provide.


No.
That could only be true if you saved it as the tif.
It would then avoid suffering the tone "consolidation" that happens when
it's re-compressed into a jpeg.
Remember, that it's in the saving, re-saving, or converting to...a
jpeg...that loss due to recompression happens.


 
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Les
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      08-23-2005

Thomas T. Veldhouse wrote:
>
> There are always small errors created when you save an image as JPEG, as
> it is a lossy compression scheme .. which means you have lost data.
> Now, when you convert to TIFF, you have lost nothing over the original
> JPEG, so the original loss is simply maintained. You then save your
> JPEG from the modified TIFF and you again apply a lossy algorithm and
> get more loss. So, the answer is the new JPEG is of lower quality [as
> far as dataloss is concerned] than the original. Having said that, if
> you never modify your new JPEG images and always work from your original
> TIFF, your loss can be considered neglible.
>

Thank you Thomas (and Mark).
Extending this discussion one step further, it seems that the ideal
situation would be to shoot in TIFF mode in the camera (to avoid the
initial compression loss). Aside from the fact that my camera won't
shoot in TIFF mode, considering the huge file sizes involved with TIFF,
would shooting in RAW mode be of any benefit? RAW seems also to also
be a compressed mode (much smaller file size than TIFF); is the RAW
compression lossless?
This is just a theoretical discussion at this point, as high quality
JPEG seems adequate for my purposes.
Thanks.

 
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Brian
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      08-23-2005
RAW files (at least the Canon CR2) are compressed losslessly - so there
isn't any quality lost to compression when you shoot a RAW file.
However, the RAW files are more of a "hassle" than JPEG in that they
require post processing.

So if you were to shoot in RAW you would download the image from the
camera, open it in a RAW conversion program (I use Adobe Camera Raw 2.4
and Raw Shooter Essentials), do the conversion and then save the
result. If you choose to save the image in a lossless format you
wouldn't lose any data from the original capture (with the exception of
whatever might be lost in the conversion). Then you could make
whatever adjustments you wanted to and save the final output as JPEG -
which would result in the file being compressed in a lossy format only
once.

Brian

 
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Jim Townsend
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      08-23-2005
Les wrote:

> I shoot in high resolution JPEG mode with my camera. I download the
> files to my computer for archiving and editing. I save each picture as
> a TIF for editing. After I complete my editing, I save the edited TIF
> as a high quality JPEG.
> My question is this: Is the edited JPEG the still same quality as the
> original JPEG downloaded from the camera?
> Thanks for any info you can provide.


What you're doing is an unecesary step. Look at the two scenarios
shown below:

- Camera saves a first generation JPEG. 1. There is some data loss.
- You save the JPEG as a TIFF. 2. There is no data loss
- You save the TIFF as a JPEG. 3. There is some data loss

This is no different than:

- Camera saves a first generation JPEG. 1. There is some data loss.
- You edit the file and save as as JPEG. 2. There is some data loss.

Note that #2 makes no difference.. You're saving a JPEG twice no
matter how you look at it.

I can't see an advantage to doing the TIFF conversion. (Not unless you
edit it over several sessions saving each time). You can save a TIFF
as much as you want without data loss.

Just as a point.. Saving as JPEG twice isn't the end of the world.

Fine JPEG and even a second generation saves of fine JPEG files really
aren't that bad.. If you make sure you use maximum JPEG compression
each time, I doubt you could see the difference between an original TIFF
and a second generation JPEG.





 
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John A. Stovall
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      08-23-2005
On 23 Aug 2005 13:51:09 -0700, "Les" <(E-Mail Removed)> wrote:

>
>Thomas T. Veldhouse wrote:
>>
>> There are always small errors created when you save an image as JPEG, as
>> it is a lossy compression scheme .. which means you have lost data.
>> Now, when you convert to TIFF, you have lost nothing over the original
>> JPEG, so the original loss is simply maintained. You then save your
>> JPEG from the modified TIFF and you again apply a lossy algorithm and
>> get more loss. So, the answer is the new JPEG is of lower quality [as
>> far as dataloss is concerned] than the original. Having said that, if
>> you never modify your new JPEG images and always work from your original
>> TIFF, your loss can be considered neglible.
>>

>Thank you Thomas (and Mark).
>Extending this discussion one step further, it seems that the ideal
>situation would be to shoot in TIFF mode in the camera (to avoid the
>initial compression loss). Aside from the fact that my camera won't
>shoot in TIFF mode, considering the huge file sizes involved with TIFF,
>would shooting in RAW mode be of any benefit? RAW seems also to also
>be a compressed mode (much smaller file size than TIFF); is the RAW
>compression lossless?
>This is just a theoretical discussion at this point, as high quality
>JPEG seems adequate for my purposes.
>Thanks.


Shot RAW. It's a lossless compression (except for Nikon and Kodak) and
you can from PhotoShop save out to any format you want.

See the below article.

http://www.cambridgeincolour.com/tut...ile-format.htm

All you want to know about RAW and compression.
************************************************** ************

"There has always been war. War is raging throughout the world
at the present moment. And there is little reason to believe
that war will cease to exist in the future. As man has become
increasingly civilized, his means of destroying his fellow man
have become ever more efficient, cruel and devastating.
Is it possible to put an end to a form of human behavior which
has existed throughout history by means of photography?
The proportions of that notion seem ridiculously out of balance.
Yet, that very idea has motivated me.

James Nachtwey
War Photographer
http://www.jamesnachtwey.com/
 
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Les
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      08-23-2005

Jim Townsend wrote:
>...
> - Camera saves a first generation JPEG. 1. There is some data loss.
> - You edit the file and save as as JPEG. 2. There is some data loss.
>
> Note that #2 makes no difference.. You're saving a JPEG twice no
> matter how you look at it.
>
> I can't see an advantage to doing the TIFF conversion. (Not unless you
> edit it over several sessions saving each time). You can save a TIFF
> as much as you want without data loss.
> ...


Jim,
The reason I convert to TIFF is because sometimes I spend a long time
editing a picture, so I do intermediate saves in case I have to
interrupt the session. Also, after printing an edited file, I might
decide to do some additional tweaks based on how the print looks.
Les

 
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MarkČ
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      08-23-2005

"Les" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed) oups.com...
>
> Jim Townsend wrote:
>>...
>> - Camera saves a first generation JPEG. 1. There is some data loss.
>> - You edit the file and save as as JPEG. 2. There is some data loss.
>>
>> Note that #2 makes no difference.. You're saving a JPEG twice no
>> matter how you look at it.
>>
>> I can't see an advantage to doing the TIFF conversion. (Not unless you
>> edit it over several sessions saving each time). You can save a TIFF
>> as much as you want without data loss.
>> ...

>
> Jim,
> The reason I convert to TIFF is because sometimes I spend a long time
> editing a picture, so I do intermediate saves in case I have to
> interrupt the session. Also, after printing an edited file, I might
> decide to do some additional tweaks based on how the print looks.
> Les


Ah. Doing intermediate saves...that would give reason for it.



 
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kombi45@yahoo.com
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Posts: n/a
 
      08-23-2005

Les wrote:
> Jim Townsend wrote:
> >...
> > - Camera saves a first generation JPEG. 1. There is some data loss.
> > - You edit the file and save as as JPEG. 2. There is some data loss.
> >
> > Note that #2 makes no difference.. You're saving a JPEG twice no
> > matter how you look at it.
> >
> > I can't see an advantage to doing the TIFF conversion. (Not unless you
> > edit it over several sessions saving each time). You can save a TIFF
> > as much as you want without data loss.
> > ...

>
> Jim,
> The reason I convert to TIFF is because sometimes I spend a long time
> editing a picture, so I do intermediate saves in case I have to
> interrupt the session. Also, after printing an edited file, I might
> decide to do some additional tweaks based on how the print looks.


If you are spending considerable time editing pictures, you might as
well shoot RAW. The RAW post workflow literally takes less than a
couple of minutes or so per picture, at most. I use RawShooter
Essentials 2005, which is free at www.pixmantec.com. Do the quick
extra step, export it to TIFF and go wild.

Ben

 
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