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From: Peabody on 20 Oct 2009 20:32
I took pictures of a friend's paintings with my superb Canon A590IS
at the camera's full 8mp. With mixed results.

Well, I thought it did ok except for the slight bowing of all the
edges. I guess I should have moved farther away and zoomed in to
reduce that.

Anyway, one of the pictures was a bit tilted, so I used a program
called Photo! Editor by VicMan Software to straighten the picture,
which seemed to go ok.

The resolution of the jpeg went from the original 3264x2488 to
3209x2406, with is about a 5% reduction in pixels as a result of
the straightening. But the file size went from the original 3296kb
down to 1191kb, a 64% reduction.

I'm hard pressed to see any visual difference. But I don't
understand why not, given the difference in file size. Can anyone
tell me what may be going on?





From: J�rgen Exner on 20 Oct 2009 21:15
Peabody <waybackNO784SPAM44(a)yahoo.com> wrote:
>Anyway, one of the pictures was a bit tilted, so I used a program
>called Photo! Editor by VicMan Software to straighten the picture,
>which seemed to go ok.
>
>The resolution of the jpeg went from the original 3264x2488 to
>3209x2406, with is about a 5% reduction in pixels as a result of
>the straightening.

5% difference as the result of some editing seems to be normal.

>But the file size went from the original 3296kb
>down to 1191kb, a 64% reduction.

Then you used a higher JPEG compression level when saving the edited
file.

>I'm hard pressed to see any visual difference. But I don't
>understand why not, given the difference in file size. Can anyone
>tell me what may be going on?

Look closely at a full-size version (there are no 3209x2406 monitors, so
you have to zoom in all the way) and you should be able to notice quite
a few more compression artifacts.
Of course, for a web page or even computer viewing it doesn't matter at
all because even high-resolution monitors are only 1/4 the size of the
picture. It only becomes relevant when you want to print a large print.

jue
From: sobriquet on 20 Oct 2009 21:19
On 21 okt, 02:32, Peabody <waybackNO784SPA...(a)yahoo.com> wrote:
> I took pictures of a friend's paintings with my superb Canon A590IS
> at the camera's full 8mp.  With mixed results.
>
> Well, I thought it did ok except for the slight bowing of all the
> edges.  I guess I should have moved farther away and zoomed in to
> reduce that.
>
> Anyway, one of the pictures was a bit tilted, so I used a program
> called Photo! Editor by VicMan Software to straighten the picture,
> which seemed to go ok.
>
> The resolution of the jpeg went from the original 3264x2488 to
> 3209x2406, with is about a 5% reduction in pixels as a result of
> the straightening.  But the file size went from the original 3296kb
> down to 1191kb, a 64% reduction.
>
> I'm hard pressed to see any visual difference.  But I don't
> understand why not, given the difference in file size.  Can anyone
> tell me what may be going on?

The quality settings for jpg compression can have a big impact on
filesize, despite
the fact that there is little or no apparent visual distinction
between the large and the smaller file.
From: Paul Furman on 20 Oct 2009 23:24
Peabody wrote:
> I took pictures of a friend's paintings with my superb Canon A590IS
> at the camera's full 8mp. With mixed results.
>
> Well, I thought it did ok except for the slight bowing of all the
> edges. I guess I should have moved farther away and zoomed in to
> reduce that.

Yep that usually helps. Barrel distortion can also be fixed with
software, I'm not sure which affordably or easily though.


> Anyway, one of the pictures was a bit tilted, so I used a program
> called Photo! Editor by VicMan Software to straighten the picture,
> which seemed to go ok.
>
> The resolution of the jpeg went from the original 3264x2488 to
> 3209x2406, with is about a 5% reduction in pixels as a result of
> the straightening. But the file size went from the original 3296kb
> down to 1191kb, a 64% reduction.
>
> I'm hard pressed to see any visual difference. But I don't
> understand why not, given the difference in file size. Can anyone
> tell me what may be going on?

Like others said, jpeg compression settings... zoom in ridiculously
close and look at smooth graded areas for blocky shapes of various sizes.

--
Paul Furman
www.edgehill.net
www.baynatives.com

all google groups messages filtered due to spam
From: More Info on 21 Oct 2009 00:06
On Tue, 20 Oct 2009 19:32:58 -0500, Peabody <waybackNO784SPAM44(a)yahoo.com>
wrote:

>I took pictures of a friend's paintings with my superb Canon A590IS
>at the camera's full 8mp. With mixed results.
>
>Well, I thought it did ok except for the slight bowing of all the
>edges. I guess I should have moved farther away and zoomed in to
>reduce that.
>
>Anyway, one of the pictures was a bit tilted, so I used a program
>called Photo! Editor by VicMan Software to straighten the picture,
>which seemed to go ok.
>
>The resolution of the jpeg went from the original 3264x2488 to
>3209x2406, with is about a 5% reduction in pixels as a result of
>the straightening. But the file size went from the original 3296kb
>down to 1191kb, a 64% reduction.
>
>I'm hard pressed to see any visual difference. But I don't
>understand why not, given the difference in file size. Can anyone
>tell me what may be going on?
>

It sounds like your editor auto-crops on rotations. Many editors have
options for this, crop or no crop on rotations. If you don't allow
auto-cropping, then long thin triangular slivers of black, white, or chosen
background color are filled-in at the edges to compensate for the now
rotated image. Filling in the gaps where the rotation can no longer match
the original file-dimension edges.

If this is an important project, I highly stress that you obtain any editor
that has Lanczos-8 (or lesser Lanczos-X versions) as a resampling algorithm
in its options. This prevents the image from losing detail during slight
rotations. Using bicubic resampling, as exists as the only option in all
versions of PhotoShop, (bicubic being the most common, fast, and acceptable
algorithm in popular use) during rotations or resizings will cause you to
lose as much as 50% of original image details due to its inherent softening
of all edge detail during resampling. I find it extremely odd that people
will easily pay more than $5000 for camera gear, then spend another $700
for an editor that causes them to lose all the details in their images,
reducing their cameras' image resolution to something they could have
bought in the toy-aisle. Some people aren't too bright.

Photoline <www.pl32.net> is an extremely good (more feature-rich and more
capable than PhotoShop in fact) inexpensive editor that has Lanczos-3 and
Lanczos-8 options for all rotations and resizings. It also includes other
algorithms (bicubic, linear, quick (whatever "quick" is)), which I
sometimes use if I intentionally want to soften image details. The
difference in retained details between a bicubic and Lanczos-8 resize or
rotation is very obvious when you have the two available to compare.

Filesize changes have already been explained to you by others.

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