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Jpeg question....

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Anonymous
January 21, 2005 3:04:33 AM

Archived from groups: rec.photo.digital (More info?)

Hi all,

Newbie question, I've googled to no avail.

I'm having difficulty figuring out the whole jpegs, compression and
resolution thing. I'm trying to cut down my images to a max of 50kb (for
ebay incidently) keeping as much quality as possible. When I re-crop and
save or reduce image size slightly, the resorting file ends up larger than
it was in the first place. I can't understand it.

Is there a program that allows you to set a maximum file size before
adjusting the image characteristics.

Any advice welcome.

Cheers,

Paul

More about : jpeg question

Anonymous
January 21, 2005 3:04:34 AM

Archived from groups: rec.photo.digital (More info?)

>I'm having difficulty figuring out the whole jpegs, compression and
>resolution thing. I'm trying to cut down my images to a max of 50kb (for
>ebay incidently) keeping as much quality as possible. When I re-crop and
>save or reduce image size slightly, the resorting file ends up larger than
>it was in the first place. I can't understand it.
>
>Is there a program that allows you to set a maximum file size before
>adjusting the image characteristics.


For most photos suitable for ebay, a 50kb file will be plenty of
resolution. This is usually a two step process, first you have to
resize the file, this isn't just cropping but changing the actual
dimensions of the photo. Every software package will have a feature
that resizes the photo. I would think that dimensions somewhere in
the area of 600X400 more or less will work pretty well. After you
have resized, which will take you a long way toward your goal you
then need to compress the file. Normally this is accomplished by just
saving it as a JPG and then choosing a percentage of compression.
Where the larger the number up to 100% will yield the best resolution
and the largest file. I find that 93% works pretty well for web pages
and probably will work pretty well for Ebay. From there you can make
minor adjustments as needed to get a good trade off between quality
and the size of the file. Once you have done this once or twice it
will become very easy for you.

I hope this helps.

Thanks
Barry
Anonymous
January 21, 2005 3:04:34 AM

Archived from groups: rec.photo.digital (More info?)

B&B Musmon wrote:
> >I'm having difficulty figuring out the whole jpegs, compression and
> >resolution thing. I'm trying to cut down my images to a max of 50kb
(for
> >ebay incidently) keeping as much quality as possible. When I re-crop
and
> >save or reduce image size slightly, the resorting file ends up
larger than
> >it was in the first place. I can't understand it.
> >
> >Is there a program that allows you to set a maximum file size before
> >adjusting the image characteristics.
>
> ... After you
> have resized, which will take you a long way toward your goal you
> then need to compress the file. Normally this is accomplished by
just
> saving it as a JPG and then choosing a percentage of compression.
> Where the larger the number up to 100% will yield the best resolution
> and the largest file. I find that 93% works pretty well.

Very good, free software to do what you need is Irfanview. Google for
it and download it from the Internet. Notice the Ebay checkboxes in
the install which may or may not be desirable for you to leave checked.

As Barry suggested, your first task is to resize/resample the image.
That reduces the dimensions of the image - making the same picture
smaller.

Then you need to write it out with "Save As", setting the "quality"
setting. One qualification to what Barry said is that the
"percentages" aren't physical size percentages. 100 doesn't means no
change in the byte count, and 50 doesn't mean half as many bytes. The
numbers in all JPEG applications are arbitrary quality settings and
you'll need to experiment with them to get the tradeoff of size and
quality that you want. If someone used, say, "90" in one application,
that may actually translate to 95, 85, or even 60 in some other
application. So you have to experiment.

Also, if your image came from a digital camera, be sure to tell
Irfanview to NOT include the EXIF data in the Save As file. The EXIF
can add 8-10K bytes that is of no use for an Ebay picture.

To my knowledge, none of the JPEG compression programs allow you to set
a maximum output size, and they couldn't easily do it because the JPEG
algorithms don't know what the output size will be until they've
actually compressed the data. So I repeat, you've got to experiment.
Alan
Related resources
Anonymous
January 21, 2005 3:04:35 AM

Archived from groups: rec.photo.digital (More info?)

Alan Meyer commented courteously ...

> To my knowledge, none of the JPEG compression
> programs allow you to set a maximum output size,
> and they couldn't easily do it because the JPEG
> algorithms don't know what the output size will be
> until they've actually compressed the data.

Not really. Paint Shop Pro's JPEG Optimizer will show you
the compressed file size in real time as you adjust the 1-
100 compression factor.

--
ATM, aka Jerry
Anonymous
January 21, 2005 3:04:35 AM

Archived from groups: rec.photo.digital (More info?)

"Alan Meyer" <ameyer2@yahoo.com> schrieb
> To my knowledge, none of the JPEG compression programs allow you to set
> a maximum output size, and they couldn't easily do it because the JPEG
> algorithms don't know what the output size will be until they've
> actually compressed the data. So I repeat, you've got to experiment.

In cPicture you can set the final file size in KB.
You either set the quality levels or the pixel size to a fixed value.
For web pictures you can also set the chrominance level to about 50 and the
luminance level to 80-90.
Anonymous
January 21, 2005 4:30:12 AM

Archived from groups: rec.photo.digital (More info?)

Paul Laup wrote:
> Hi all,
>
> Newbie question, I've googled to no avail.
>
> I'm having difficulty figuring out the whole jpegs, compression and
> resolution thing. I'm trying to cut down my images to a max of 50kb (for
> ebay incidently) keeping as much quality as possible. When I re-crop and
> save or reduce image size slightly, the resorting file ends up larger than
> it was in the first place. I can't understand it.
>
> Is there a program that allows you to set a maximum file size before
> adjusting the image characteristics.
>
> Any advice welcome.
>
> Cheers,
>
> Paul
>
>

You want to set the dimensions (pixels wide x pixels high) based on the amount
of screen space you want to use for the image, then set the compression to get
the file down to the size you want. A big image will be 800x600, and thumbnails
might be 120x90. 80% quality will look as good as 100% quality, but may still
result in 200k files. Try 50% or 60% quality.

--
--
Ben Thomas - Software Engineer - Melbourne, Australia

My Digital World:
Kodak DX6490, Canon i9950, Pioneer A05;
Hitachi 37" HD plasma display, DGTEC 2000A,
Denon 2800, H/K AVR4500, Whatmough Encore;
Sony Ericsson K700i, Palm Tungsten T.

Disclaimer:
Opinions, conclusions, and other information in this message that do not
relate to the official business of my employer shall be understood as neither
given nor endorsed by it.
January 21, 2005 5:35:28 AM

Archived from groups: rec.photo.digital (More info?)

In article <cbt0v0ptcnsprm6paiertrbrlnrqb0podp@4ax.com>, barrym@tdstelme.net
says...
>
>>I'm having difficulty figuring out the whole jpegs, compression and
>>resolution thing. I'm trying to cut down my images to a max of 50kb (for
>>ebay incidently) keeping as much quality as possible. When I re-crop and
>>save or reduce image size slightly, the resorting file ends up larger than
>>it was in the first place. I can't understand it.
>>
>>Is there a program that allows you to set a maximum file size before
>>adjusting the image characteristics.
>
>
>For most photos suitable for ebay, a 50kb file will be plenty of
>resolution. This is usually a two step process, first you have to
>resize the file, this isn't just cropping but changing the actual
>dimensions of the photo. Every software package will have a feature
>that resizes the photo. I would think that dimensions somewhere in
>the area of 600X400 more or less will work pretty well. After you
>have resized, which will take you a long way toward your goal you
>then need to compress the file. Normally this is accomplished by just
>saving it as a JPG and then choosing a percentage of compression.
>Where the larger the number up to 100% will yield the best resolution
>and the largest file. I find that 93% works pretty well for web pages
>and probably will work pretty well for Ebay. From there you can make
>minor adjustments as needed to get a good trade off between quality
>and the size of the file. Once you have done this once or twice it
>will become very easy for you.
>
>I hope this helps.
>
>Thanks
>Barry

One adjunct to Barry's suggestion. When doing the re-sizing, monitors can not
deal with much beyond 120ppi, so you don't want your 600x400 to have a ppi of
300, or more, 120 will be better than most monitors can handle, though that
figure is creeping up.

Hunt
Anonymous
January 21, 2005 2:44:09 PM

Archived from groups: rec.photo.digital (More info?)

Paul Laup wrote:

> Hi all,
>
> Newbie question, I've googled to no avail.
>
> I'm having difficulty figuring out the whole jpegs, compression and
> resolution thing. I'm trying to cut down my images to a max of 50kb (for
> ebay incidently) keeping as much quality as possible. When I re-crop and
> save or reduce image size slightly, the resorting file ends up larger than
> it was in the first place. I can't understand it.
>
> Is there a program that allows you to set a maximum file size before
> adjusting the image characteristics.

You tend to get poor results by aiming for a fixed file size. JPEG
compression is very data dependent. Several JPEG optimisers will show
you in realtime what the JPEG file would look like and how long it would
take to download on a 56k dialup.

I quite like JPEG Optimiser for this since it also allows regions of
interest to be less compressed than the flat backgrounds.

PSPro 8+ also has a realtime image optimiser wizard but is not as good.

Be sure to size the picture for the destination rectangle. No point
having an 800x600 image displayed in an 80x60 box!

A rough JPEG quality setting of either 20 or 80 out of 100 depending on
the convention used by your software is a fair starting point.

Regards,
Martin Brown
Anonymous
January 21, 2005 2:44:10 PM

Archived from groups: rec.photo.digital (More info?)

Martin Brown commented courteously ...

[snip]
> I quite like JPEG Optimiser for this since it also
> allows regions of interest to be less compressed than
> the flat backgrounds.
>
> PSPro 8+ also has a realtime image optimiser wizard
> but is not as good.
[snip]

I've found PSP 8 and 9's JPEG Optimizer an extremely
valuable asset, and one that I've never had a problem with
so long as I keep the compression factor reasonable.

> A rough JPEG quality setting of either 20 or 80 out
> of 100 depending on the convention used by your
> software is a fair starting point.

I always re-open my just-saved JPEGs to be sure there're
no artifacts or any other kind of image degradation. And,
for all of my pictures, I find that 15 is about the
highest compression I can go without seeing artifacts.
Sometimes I have to go to 18 or so to get the file size
reasonable, but seldom

--
ATM, aka Jerry
Anonymous
January 21, 2005 4:38:30 PM

Archived from groups: rec.photo.digital (More info?)

Hi,

In Irfanview, (a free image viewer that you can download from
www.irfanview.com)
you can specify the picture size you ultimately want like 1024x768, 800x600,
etc. Just go to Image > Resize/Resample and choose your size.
Just don't forget to save the picture.
Rosita
Anonymous
January 21, 2005 4:47:03 PM

Archived from groups: rec.photo.digital (More info?)

On Thu, 20 Jan 2005 19:52:19 -0600, All Things Mopar
<usenetMAPS123@comcast.net> wrote:

>Alan Meyer commented courteously ...
>
>> To my knowledge, none of the JPEG compression
>> programs allow you to set a maximum output size,
>> and they couldn't easily do it because the JPEG
>> algorithms don't know what the output size will be
>> until they've actually compressed the data.
>
>Not really. Paint Shop Pro's JPEG Optimizer will show you
>the compressed file size in real time as you adjust the 1-
>100 compression factor.

It will either (a) be guessing at the size, in which case it will sometimes
get it wrong, or (b) performing the compression and then telling you the
size.

Regards,
Graham Holden (g-holden AT dircon DOT co DOT uk)
--
There are 10 types of people in the world;
those that understand binary and those that don't.
January 21, 2005 6:41:01 PM

Archived from groups: rec.photo.digital (More info?)

"Alan Meyer" <ameyer2@yahoo.com> wrote in news:1106270539.188098.325190
@f14g2000cwb.googlegroups.com:

> To my knowledge, none of the JPEG compression programs allow you to set
> a maximum output size, and they couldn't easily do it because the JPEG
> algorithms don't know what the output size will be until they've
> actually compressed the data. So I repeat, you've got to experiment.
>

Photoshop's "Save for Web" will go ahead and calculate the compression
and give you the final file size, along with side-by-side comparisons. It
also has an "Optimize to File Size" option, where you can tell it how
many K to make the final file. It will only go so far though. If you have
a 5 mp image and tell it to make it 50k, even the lowest quality settings
result in a 142K image (for the specific image I'm looking at right now).

For the purpose of Ebay, you don't really need to resample, because Ebay
will do that anyway (making them much smaller than 640x480). It does save
on upload time if you have a slow connection though.

Bob
Anonymous
January 21, 2005 11:55:13 PM

Archived from groups: rec.photo.digital (More info?)

In article <1106270539.188098.325190@f14g2000cwb.googlegroups.com>,
Alan Meyer <ameyer2@yahoo.com> wrote:
> [clip]
>
>To my knowledge, none of the JPEG compression programs allow you to set
>a maximum output size, and they couldn't easily do it because the JPEG
>algorithms don't know what the output size will be until they've
>actually compressed the data. So I repeat, you've got to experiment.
>Alan
>

Photoshop CS has an "Optimize to File Size" option in its "Save For
Web". You enter the desired file size in "K" bytes. The "Optimize
To File Size" window is found from the "Save For Web" window by
clicking the round, right-pointing arrow to the right of the
'Preset' pulldown. After entering the value, Photoshop CS tells you
how big the file is and what compression quality value it chose.
Anonymous
January 22, 2005 12:24:39 PM

Archived from groups: rec.photo.digital (More info?)

On 20 Jan 2005 17:22:19 -0800, "Alan Meyer" <ameyer2@yahoo.com> wrote:

>To my knowledge, none of the JPEG compression programs allow you to set
>a maximum output size, and they couldn't easily do it because the JPEG
>algorithms don't know what the output size will be until they've
>actually compressed the data. So I repeat, you've got to experiment.

Why couldn't the program do the experimenting for you? jpegsizer allows
you to set the size wanted; I assume it does it by trial and error.

--
Stephen Poley
!