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better to compress the jpeg or reduce resolution or reduce pixel size?

 
 
Mr.Will
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      09-23-2004
Heya guys,

If anyone can offer me some science on the matter I'd be most grateful. I am
taking shots at high jpeg setting on my Canon d60. These files come out
between 3 and 4 Mb.

The people that want the photos want the size to be no bigger than 2mb so
that their server can handle each one. Problem is, with photoshop I arent
entirely sure what is the best way of achieving this file size, or how to
calculate it without saving as a different filename and previewing using the
"properties" of the image icon.

If I reduce resolution this brings down the file size, as does reducing the
image dimensions (pixels) as does compressing. Which would you reccomend as
the best method? I notice photoshop has THREE maximum settings (10,11,12).

Also I arent entirely sure how much of each does to the filesize. For
instance I started with a 3 mb file, I reduced it in size and saved it, and
the file, despite being smaller was now 3.5 mb!!!

Any light ANYONE can shed will be most appreciated.

Mr.Will


 
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Not Dick Daley
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      09-23-2004
If you decrease the resolution of the pictures via Photoshop, Paint Shop Pro
etc....you're losing picture image quality.

If you simply reduce the photo size in the camera, it will be more than
sufficient for viewing, unless you're going to blow these things up.

It's best likened to developing an 8X10 of a photo that was shot at 100 ISO,
to doing the same picture 8X10 of a photo using 800 ISO.

I use Paint Shop Pro's Photo Album sofware. It's GREAT for batch resizing
(or renaming) of photo's. I can do 50 12MB files into 50 500k files in
about 20 minutes. If you did them individually....it'd take all night!

Hope this helped you a bit.


"Mr.Will" <(E-Mail Removed)> wrote in message
news:V6I4d.226$(E-Mail Removed)...
> Heya guys,
>
> If anyone can offer me some science on the matter I'd be most grateful. I

am
> taking shots at high jpeg setting on my Canon d60. These files come out
> between 3 and 4 Mb.
>
> The people that want the photos want the size to be no bigger than 2mb so
> that their server can handle each one. Problem is, with photoshop I arent
> entirely sure what is the best way of achieving this file size, or how to
> calculate it without saving as a different filename and previewing using

the
> "properties" of the image icon.
>
> If I reduce resolution this brings down the file size, as does reducing

the
> image dimensions (pixels) as does compressing. Which would you reccomend

as
> the best method? I notice photoshop has THREE maximum settings (10,11,12).
>
> Also I arent entirely sure how much of each does to the filesize. For
> instance I started with a 3 mb file, I reduced it in size and saved it,

and
> the file, despite being smaller was now 3.5 mb!!!
>
> Any light ANYONE can shed will be most appreciated.
>
> Mr.Will
>
>



 
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Peter
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      09-23-2004
On Thu, 23 Sep 2004 22:29:09 GMT, Mr.Will wrote:

> If anyone can offer me some science on the matter I'd be most grateful. I am
> taking shots at high jpeg setting on my Canon d60. These files come out
> between 3 and 4 Mb.
>
> The people that want the photos want the size to be no bigger than 2mb so
> that their server can handle each one....


The pixel dimensions you want are primarily determined by how someone will
view your images. If they're always going to be viewed on a 800x600
computer screen, there is no point in making the image pixel size bigger
than that. On the other hand, if the images are going to be printed in high
quality, you should plan on 100-300 pixels per inch of printed size. (This
wide range reflects differing opinions on this).

Once you have determined the pixel dimensions, the file size will be
determined by the amount of detail in each image and by the JPEG
compression level (or inversely the quality setting).

[In tests I conducted on photo images with the same pixel dimensions and
the same JPEG compression level, file sizes vary over a range of more than
3-to-1, depending on the detail present in the images.]

Sounds like you could use a versatile image resizer that will automatically
figure out what JPEG compression level is needed to achieve your desired
file size. Suggest you try the link below.

Peter
--

================================================== =======
Need to resize images for email attachments or web pages?
Try Jpeg Sizer at: http://www.tangotools.com?s=ng
================================================== =======
 
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Bob
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      09-24-2004
On Thu, 23 Sep 2004 22:29:09 GMT, "Mr.Will" <(E-Mail Removed)> wrote:

>Heya guys,
>
>If anyone can offer me some science on the matter I'd be most grateful. I am
>taking shots at high jpeg setting on my Canon d60. These files come out
>between 3 and 4 Mb.
>
>The people that want the photos want the size to be no bigger than 2mb so
>that their server can handle each one.


First - you need to know what dimensions are needed, not the file size...

Once you know that, you can worry about the file size...

But generally speaking, for the Internet, you decrease file size by increasing
the compression of the image. This is because Internet images are usually just
for viewing, and not blowing up or printing, therefore you can get away with
huge compressions.

On my own web site, I re-size to 1024x680 or so, to fit the biggest screen, and
then I compress to an average 125k bytes. The originals are 3m, 3000x2000....

I use Micrografx software but Photoshop has a 'quality' option in saving as
well.

You need to manipulate both the image size and image compression to achieve the
results you want.


>Problem is, with photoshop I arent
>entirely sure what is the best way of achieving this file size, or how to
>calculate it without saving as a different filename and previewing using the
>"properties" of the image icon.
>
>If I reduce resolution this brings down the file size, as does reducing the
>image dimensions (pixels) as does compressing. Which would you reccomend as
>the best method? I notice photoshop has THREE maximum settings (10,11,12).
>
>Also I arent entirely sure how much of each does to the filesize. For
>instance I started with a 3 mb file, I reduced it in size and saved it, and
>the file, despite being smaller was now 3.5 mb!!!
>
>Any light ANYONE can shed will be most appreciated.
>
>Mr.Will
>


 
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Tony Morgan
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Posts: n/a
 
      09-24-2004
In message <(E-Mail Removed)>, Not Dick Daley
<(E-Mail Removed)> writes
Snipped...

>It's best likened to developing an 8X10 of a photo that was shot at 100
>ISO, to doing the same picture 8X10 of a photo using 800 ISO.


Really? I always thought that the higher ISO introduced noise and not
artefacts, but that it did not reduce resolution.

In answer to the OP, I'd suggest that it's best to shoot at max
resolution (pixels) and minimum compression, then to resample to the
size that you require in your photo editing software.
--
Tony Morgan
http://www.camcord.info
 
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Tony Morgan
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Posts: n/a
 
      09-24-2004
In message <(E-Mail Removed)>, Bob
<(E-Mail Removed)> writes
>But generally speaking, for the Internet, you decrease file size by
>increasing the compression of the image.


Do so with great care. Increasing compression introduces artefacts. And
never resize (again it introduces artefacts), but rather resample to
size.
--
Tony Morgan
http://www.camcord.info
 
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Wouter Wessels
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Posts: n/a
 
      10-07-2004
In article <V6I4d.226$(E-Mail Removed)>,
"Mr.Will" <(E-Mail Removed)> wrote:

> Heya guys,
>
> If anyone can offer me some science on the matter I'd be most grateful. I am
> taking shots at high jpeg setting on my Canon d60. These files come out
> between 3 and 4 Mb.
>
> The people that want the photos want the size to be no bigger than 2mb so
> that their server can handle each one. Problem is, with photoshop I arent
> entirely sure what is the best way of achieving this file size, or how to
> calculate it without saving as a different filename and previewing using the
> "properties" of the image icon.
>
> If I reduce resolution this brings down the file size, as does reducing the
> image dimensions (pixels) as does compressing. Which would you reccomend as
> the best method? I notice photoshop has THREE maximum settings (10,11,12).
>
> Also I arent entirely sure how much of each does to the filesize. For
> instance I started with a 3 mb file, I reduced it in size and saved it, and
> the file, despite being smaller was now 3.5 mb!!!
>
> Any light ANYONE can shed will be most appreciated.
>
> Mr.Will


Mr.Will,

Because I had sorta the same question you have, I have done some tests.
I have a 5 Megapixel Canon S60 camera. I ever changed the resolution of
the images or the camera ... all images/files are, and will always be 5
MegaPixels.

1) Take photo in factory default 'Fine' 5MPixel.
2) Take photo in 'Super Fine' 5 MPixel (probably default on D60)
3) Take photo in RAW

Here are the sizes:
1) 1500 KBytes
2) 2500 KBytes
3) 5200 KBytes

Then I lokked at the cmpression I could get:
1) Save the RAW image as JPG with 100% quality
2) Save the RAW image as JPG with 90% quality
3) Save the RAW image as JPG with 80% quality

This gave the following sizes:
1) 3600 KBytes
2) 1000 KBytes
3) 800 KBytes

Here was the amazing part:
When comparing the follwing photos:
- RAW
- the 100% compressed jpeg (3600 KByte)
- the 90% jpeg (1000 KByte)
- the 'Fine' photo (1500 KByte)

I could barely see the difference between the first 3, and the Fine
photo showed much more compression artifacts than the rest.

My conclusion was that the camera does a bad job at compressing: It
compresses to a larger file, with more damage to the photo. That is not
a big surprise, because the camera has to be optimised for SPEED, while
the computer that compresses the image is probably way faster, and is
optimized for quality!

So ... From now on, I take all photos in RAW 'Super Fine' and when I
need the files smaller, I compress them on my computer ...

Translating that to your 6.3 MPixels ... the file sizes would be
somewhat bigger, but probably only by about 20% ... I guess if you do
the same tests, you'd come to more or less the same answers.
Please do those tests yourself ... do not believe everything you read
here ...

Have fun with it,

Wouter


--

Wouter F. Wessels
Gouda, the Netherlands
http://www.wwessels.cistron.nl/picofday.shtml
(E-Mail Removed)
 
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Pete
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      10-08-2004

I always capture photos in the camera with the highest available JPEG
quality (although some perfectionists use TIFF or RAW). These are the only
ways to ensure that the images will be suitable for any future purpose you
might encounter.

For Internet images, I agree with others here: figure out the pixel
dimensions first, then the JPEG compression level.

If an image is going to be displayed on a computer screen, there's no point
in delivering more pixels than will fit without scaling, and there are
still a lot of 800x600 monitors out there. 640x480 images are good, because
task bars etc consume screen real estate.

When it comes to compressing, most programs only let you specify the JPEG
quality (or compression) level. The file size you get is unpredictable, and
varies over a range of at least 3-to-1, depending on the amount of detail
in each photo.

JpegSizer is a batch resizing utility that will let you specify the file
size you want, and it figures out automatically what compression is needed
to achieve that file size. You can find it at

http://www.tangotools.com/jpegsizer/?s=ng

It's a little unusual to post images as large as 2MB. PhotoSIG for example
has a limit of 300KB, and there are plenty of superb images on there. IMO,
anything more than that is only needed if the recipient will output large
high-quality prints, in which case the pixel dimensions should also be
higher. In these situations, I'd recommend that you keep the original pixel
dimensions, and simply compress down to the desired file size.

Hope this helps

Pete
 
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John McWilliams
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      10-08-2004
Pete wrote:

> I always capture photos in the camera with the highest available JPEG
> quality (although some perfectionists use TIFF or RAW). These are the only
> ways to ensure that the images will be suitable for any future purpose you
> might encounter.
>
> For Internet images, I agree with others here: figure out the pixel
> dimensions first, then the JPEG compression level.
>
> If an image is going to be displayed on a computer screen, there's no point
> in delivering more pixels than will fit without scaling, and there are
> still a lot of 800x600 monitors out there. 640x480 images are good, because
> task bars etc consume screen real estate.
>

Since the OP said he had Photoshop, here is a fool proof method (until
we can create better fools.....)

Go to Edit menu, Save for Web. In right hand dialogue, lower box, change
width of image to 640 pixels, leaving "constrain proportions" checked.
Then choose jpeg above, and save at medium quality. Now send the result
to a friend, cc to yourself.

And the original image is untouched so you can keep the higher
resolution to print later.

--
John McWilliams
 
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