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Re-sizing high res pictures



 
 
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  #1  
Old July 28th 06, 03:51 PM posted to rec.photo.digital
[email protected]
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Posts: 2
Default Re-sizing high res pictures

I am taking pictures for a website at 2560x1920 px, and then re-sizing
them to 448x336 px before uploading them to the website so they do not
take up a customer's entire screen when viewed on the site. Am I
losing quality in the photos? Also, is this just a waste of card space?

  #5  
Old July 29th 06, 01:34 AM posted to rec.photo.digital
k-man
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Posts: 106
Default Re-sizing high res pictures

If you plan on doing any editing, I'd say take them at full res, edit
and then shrink rather than trying to edit the smaller versions.

By losing quality, what do you mean... are you asking whether the
smaller photos will be of lesser quality such that they simply don't
look as good on the web site in their smaller form as they do in full
size on your computer screen? Or are you not talking about looks but
rather attributes such as pixel count and print size? When you shrink
a photo, you will loose both the total number of available pixels and
print size (print size will still exist, but it will be smaller). In
terms of looks, I think it depends on the image in your picture. If
your image is busy, then sometimes you'll wish the pic were larger so
that you can more clearly see the detail. For cleaner shots, like
portraits, smaller pics can look quite good.

It can depend also on what you're going to do with the pics. Look at
the news sites, like CNN. Even if the pics are taken at full res, most
of the time the pics are cropped and/or just slapped up to the web site
as-is.

Kevin






wrote:
I am taking pictures for a website at 2560x1920 px, and then re-sizing
them to 448x336 px before uploading them to the website so they do not
take up a customer's entire screen when viewed on the site. Am I
losing quality in the photos? Also, is this just a waste of card space?


  #7  
Old July 29th 06, 03:03 AM posted to rec.photo.digital
k-man
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Posts: 106
Default Re-sizing high res pictures

And by "as-is" I mean without editing, not without resizing.

Thanks.
Kevin


k-man wrote:
If you plan on doing any editing, I'd say take them at full res, edit
and then shrink rather than trying to edit the smaller versions.

By losing quality, what do you mean... are you asking whether the
smaller photos will be of lesser quality such that they simply don't
look as good on the web site in their smaller form as they do in full
size on your computer screen? Or are you not talking about looks but
rather attributes such as pixel count and print size? When you shrink
a photo, you will loose both the total number of available pixels and
print size (print size will still exist, but it will be smaller). In
terms of looks, I think it depends on the image in your picture. If
your image is busy, then sometimes you'll wish the pic were larger so
that you can more clearly see the detail. For cleaner shots, like
portraits, smaller pics can look quite good.

It can depend also on what you're going to do with the pics. Look at
the news sites, like CNN. Even if the pics are taken at full res, most
of the time the pics are cropped and/or just slapped up to the web site
as-is.

Kevin






wrote:
I am taking pictures for a website at 2560x1920 px, and then re-sizing
them to 448x336 px before uploading them to the website so they do not
take up a customer's entire screen when viewed on the site. Am I
losing quality in the photos? Also, is this just a waste of card space?


  #8  
Old July 29th 06, 06:55 PM posted to rec.photo.digital
y_p_w
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Posts: 43
Default Re-sizing high res pictures



Bob Williams wrote:


wrote:

I am taking pictures for a website at 2560x1920 px, and then re-sizing
them to 448x336 px before uploading them to the website so they do not
take up a customer's entire screen when viewed on the site. Am I
losing quality in the photos? Also, is this just a waste of card space?

Most cameras have the ability to capture images at different sizes.
If you KNOW that a particular image will be uploaded to a website, you
can save card space by shooting at a reduced size. However you will
still lose image quality by doing so.
Your camera captures all images at 2560x1920 pixels. Only when you SAVE
the image to the memory card is the size reduced (Resampled)
Your photo editor may use a better resampling algorithm than the camera,
but I doubt that anyone could tell the difference when displayed at
448x336 pixels.


I like having a choice in which algorithm to use. My tool of
choice is Graphic Converter for OSX. It has several algorithms
available. I like the "Smooth" algorithm, although some
combinations of downsizing produce a grid-like pattern in areas
of blue sky. Some simple downsizing (especially MS Paint) will
produce "jaggies" on diagonal edges.

I'm not 100% sure what a camera might use, although most of
what I've seen is going to require some sort of conversion
that's more complicated than combining four pixels into one.

Here are two versions of the same picture (Dennis Eckersley
in celebration of his Baseball Hall of Fame induction). The
original was 2048x1536, and the downsized versions are 25%
reduced in each dimension (512x384) using Smooth and Bicubic.
Each was then sharpened 15% (normal) and saved at 80% as
suggested by another poster.

Here's the "Smooth" version. I think it has the appearance
of less sharpness and detail, but the edges of the Corvette
look straight.

http://img205.imageshack.us/my.php?image=ecksmoothdv2.jpg

With Bicubic, the overall look is sharper, but there's a
very noticeable "jaggie" along the back end and trunk line
of the Corvette.

http://img205.imageshack.us/my.php?image=eckbicubictk7.jpg

  #9  
Old July 30th 06, 12:38 AM posted to rec.photo.digital
Bart van der Wolf
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Posts: 314
Default Re-sizing high res pictures


wrote in message
oups.com...
I am taking pictures for a website at 2560x1920 px, and then
re-sizing
them to 448x336 px before uploading them to the website so they do
not
take up a customer's entire screen when viewed on the site. Am I
losing quality in the photos? Also, is this just a waste of card
space?


You are obviously losing information by tossing out pixels, just make
sure you don't add degrading (aliasing) artifacts and lose quality as
well, by using the wrong down-sampling algorithm:
http://www.xs4all.nl/~bvdwolf/main/foto/down_sample/down_sample.htm
and
http://www.xs4all.nl/~bvdwolf/main/foto/down_sample/example1.htm

--
Bart

 




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