Photo Quality to Web Quality

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    Can some of you who are good with graphics tell me any
standards I need to consider in converting photo quality (4.1
megapixel or better) images into images that are suitable for Web

    I have a number of photos that I want to use on the Web.  I'm
sure there are some 'rules of thumb' to follow to achieve a high
degree of picture quality without creating enormous download files.  

    Any feedback or links to this type of information would be
greatly appreciated.  



Re: Photo Quality to Web Quality

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Set the .jpg quality to 100% then resize to the exact size you want. Some
resizer programmes are better than others.
Never rely on the browser to resize as it will take far too much bandwidth
and look horrible.

Re: Photo Quality to Web Quality

Mark Hewitt wrote:
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I would add that _after_ the resize, _then_ reset the .jpg quality
to as low as it will go without your being able to easily see
the difference with your eye.  (You might want to recheck
on another monitor if you have one.)

This will often allow you to cut the download time
for that particular .jpg image in half or better.

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Re: Photo Quality to Web Quality

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Funny you should say this!

As you may remember, I was required by circumstance to switch from
film SLR to digital SLR recently, and at the time was completely naive
about digital photography - though not digital imaging.

From my own experiences....

Digital cameras quote their resolution as "megapixels", such as
perhaps 6.1 mega pixels or 10 mega pixels etc.

This resolution only has bearing on the physical size of the developed
image (whether that be on screen or paper).

Professional printed images need to be printed at 300dpi, ergo a
photograph on paper ten inches wide needs to be 300 x 10 = 3000 pixels

VDU screens work at much lower resolution, and we normally only
display images at a maximum of perhaps 1024 or 1600 pixels wide.

As such, the DSLR resolution is not highly relevant for web
publishing. UNLESS one is taking long range photographs, and the
subject is very small within the image. The photo is then cropped, and
obviously higher resolution is required.

With film one encounters the ASA or ISO rating, such as 100, 200, 400
or 800 etc. With digital this equates to sensitivity (sensitivity to
light), and applies itself in practical terms in graininess of the
image. Quality photographs are those taken with as low sensitivity
(ISO setting) as possible - don't even consider 800 or higher unless
you like salt and pepper dusted all over your pictures.

There are two basic types of digital image: compressed and
uncompressed (also known as RAW).

In theory, uncompressed, such as BMP, will give better quality than
compressed, such as Jpeg. However, the Jpeg compression algorithm is
so good that even at perhaps 10 or 15% compression many people will
not notice a degradation in quality, and at 0% compression the image
will be as good as an uncompressed version, but far smaller.

The best thing is to experiment with the level of compression for you
own particular image - different images will accept varying levels of
compression before quality degradation sets in.

As for me, I usually use Jpeg with a 15% compression factor for web
photos and Jpeg with 0% compresson for storage of images I wish to

Naturally, the physical size of the image, width and height in pixels,
has a noticeable effect upon the file size.


The Probert Encyclopaedia

Re: Photo Quality to Web Quality

Matt Probert wrote:
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True to a certain extent.  But this is completely dependent on the
resolution of the display/print device.

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That depends entirely on the printer you're using.  Professionals use
cameras with 16Mb or more, and printers with a resolution of 2400dpi or
higher.  300 dpi doesn't work for them.

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Again, it depends on what you need.  Even though I'm not a professional,
I've used ASA 800 a fair amount in the past.  It's great for low-light
situations; it also has less blur on moving subjects.  However, you
can't blow it up that much.  It used to be even an 8x10 would be grainy,
but that's not true any more, at least to the inexperienced eye.  Of
course, a professional could tell the difference immediately.

<snip other stuff which I have no comment on :-)>

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Remove the "x" from my email address
Jerry Stuckle
JDS Computer Training Corp.

Re: Photo Quality to Web Quality

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It is not the answer to your question,
but just to remind you, in case you will need
some photo gallery index page with lots of thumbnails,
that usually it is quite easy to retrieve
the thumbnail image embedded in digital camera images
from the EXIF data. As an example for PHP,
there is the exif_thumbnail function

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