Re: How much should I compress Jpegs?
- From: Albert Ross <spam@xxxxxxxxxxxxxxxxxxx>
- Date: Fri, 05 Mar 2010 22:47:27 +0000
On Thu, 4 Mar 2010 08:40:36 +0000, Surfer! <surfer@xxxxxxxxx> wrote:
In message <fasto5l9pnboiorq2a7vsqbovmqfldj1gk@xxxxxxx>, Scotius
On Mon, 29 Jun 2009 20:06:36 -0700, "Walter R." <wr@xxxxxxxxxxx>
I am scanning a few family photoalbums, nothing critical or important.
Rather than scan to tiff and then to convert to jpg, I decided to scan
directly to jpg in order to save a step.
I set the compression to 15% and cannot tell the difference between the tiff
and the jpg on my computer screen. The file for a tiff is about 4 MB, for
the same compressed jpg about 400 kb (10%), a substantial saving in file
size. It adds up if you scan 1000 photos.
I've noticed that you can't really tell much difference on
screen between TIFFs and JPG photos. I think the main difference is
when they get used in print material.
TIFF exhibits millions of colors, which is why the photo is so
much larger. JPG doesn't, but you probably won't notice much
difference on the screen. Then again, there are people now who are
saying that with cameras getting so advanced, JPGs are good enough to
use in print. I'm sure to some degree this is true, but if you work
with Photoshop, it's probably easier to select out certain areas of a
photo (just the ones you want) if the colors are better defined, which
in a TIFF they would be.
What % compression do most people use for scanning to jpgs? I know, it is a
compromise between quality and file size. How do most people compromise?
The big difference between TIFF and JPG is that JPG is a losey format -
you can't ever get back to the original - and if you keep altering and
resaving a JPG the quality can go downhill. How much varies. You are
right that a TIFF *can also contain more colours than a JPG, but we
don't know what colour depth the OP was saving TIFFs with.
Agreed, I've made some A2 prints from ex-camera jpgs which are pretty
competent, but I edited them in one hit, didn't do any large
adjustments and only saved them once.
Once you start to re-work and resave them the quality breaks down. You
can see the same effect on screen when you enlarge them - it makes the
artifacts more noticeable, blockiness and loss of detail being most
obvious. But for general web/screen use it's surprising how much
compression you hardly notice.
Same for mpegs and digital TV, up to a point the quality looks fine
but go one more step in compression and the quality falls off
dramatically. A nature programme on BBC can look quite amazing but CSI
on Channel 5 at half the bitrate looks like crap with the actors' skin
texture going missing while they're in motion and appearing like a
crop of pimples when their faces are still.
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