Multiple geometric transforms vs interpolation

I had a picture that was slightly off-vertical. To put it on the web
I wanted to first rotate it by a few degrees, then resize it to web
resolution (about 0.3x). I used GIMP and selected bicubic
interpolation for both transforms and the result still came out a
little bit blurry. I'm wondering if the interpolations (which by
definition computes each destination pixel from several source pixels)
get worse as they are compounded. Maybe photo editors should keep
track of these transformations as you do them on-screen, and combine
them into a single transformation matrix (or different matrices for
different regions of the picture as you cut and paste). Then at the
end you'd re-transform the picture (i.e. go from the initial to final
picture) in a single pass, without all the intermediate steps. In
that way you'd only be interpolating once instead of several times.

Do any editing programs do that? Is there a way to get GIMP to do it?
Does it make sense?

Paul Rubin wrote:
I had a picture that was slightly off-vertical. To put it on the web
I wanted to first rotate it by a few degrees, then resize it to web
resolution (about 0.3x). I used GIMP and selected bicubic
interpolation for both transforms and the result still came out a
little bit blurry. I'm wondering if the interpolations (which by
definition computes each destination pixel from several source pixels)
get worse as they are compounded. Maybe photo editors should keep
track of these transformations as you do them on-screen, and combine
them into a single transformation matrix (or different matrices for
different regions of the picture as you cut and paste). Then at the
end you'd re-transform the picture (i.e. go from the initial to final
picture) in a single pass, without all the intermediate steps. In
that way you'd only be interpolating once instead of several times.

Do any editing programs do that? Is there a way to get GIMP to do it?
Does it make sense?
What you are saying makes sense on a theoretical basis but on a
practical level it normally will not have that much effect.

In Photoshop Elements III I can do a rotate and resize at the same time
using the crop tool, I don't know if gimp can do this.

Scott

"Scott W" wrote in message
oups.com...
Paul Rubin wrote:
I had a picture that was slightly off-vertical. To put it on the web
I wanted to first rotate it by a few degrees, then resize it to web
resolution (about 0.3x). I used GIMP and selected bicubic
interpolation for both transforms and the result still came out a
little bit blurry. I'm wondering if the interpolations (which by
definition computes each destination pixel from several source pixels)
get worse as they are compounded. Maybe photo editors should keep
track of these transformations as you do them on-screen, and combine
them into a single transformation matrix (or different matrices for
different regions of the picture as you cut and paste). Then at the
end you'd re-transform the picture (i.e. go from the initial to final
picture) in a single pass, without all the intermediate steps. In
that way you'd only be interpolating once instead of several times.

Do any editing programs do that? Is there a way to get GIMP to do it?
Does it make sense?
What you are saying makes sense on a theoretical basis but on a
practical level it normally will not have that much effect.

In Photoshop Elements III I can do a rotate and resize at the same time
using the crop tool, I don't know if gimp can do this.

Scott


Photoshop and Elements can also do it by using the Crop Tool, and in less
clicks.

The real answer is to use a non lossy format (Tiff ) for Edits which affect
pixels. But it is actually the "Saves" following the Edits which cause most
of the problem.

If it was an image from a Digital Camera, it could also be that the Camera
was set to apply too much sharpening to the Jpeg. Sharpening is almost
always best kept to the very end of the workflow.

Roy G

"Tesco News" writes:
In Photoshop Elements III I can do a rotate and resize at the same time
using the crop tool, I don't know if gimp can do this.
Photoshop and Elements can also do it by using the Crop Tool, and in less
clicks.
The real answer is to use a non lossy format (Tiff ) for Edits which affect
pixels. But it is actually the "Saves" following the Edits which cause most
of the problem.

I'm talking about doing multiple edits in one session, not saving
between the edits. Question is whether the multiple interpolations
messes up the image.

Fancier editing might mean an even longer chain of interpolations:

- rotate image
- adjust perspective using grid lines in in editor
- rotate post-perspective-adjusted image
- scale image and paste a selection from it into a composite image
- do similar steps with some other image, pasting into same composite
- scale the composite image for the web

Also, when editing it's nice to be able to see all the intermediate steps.

The original pic was a fine-resolution jpeg, if that matters.

BEEN DREAMING OF LIVING THE GOOD LIFE, ON YOUR TERMS? YOU CAN DO
THIS!


You will now become part of a Mail Order business. In this business
the
product is not solid or tangible, it's a service. You are in the
business
of developing Mailing Lists. You deal with information, and
information is
power. Many large corporations are happy to pay vast amounts for
quality
lists. However, the money made from the mailing lists is secondary to
the
income which is made from people like you and me asking to be included
on
such a list.


I used to work my butt off for someone else, but not any more. Getting
on
to the internet changed everything. I came across an article that said
you
could make thousands of dollars within weeks with a once only
investment of
$6.00! "Yeah, right, what a scam," is what I thought. I was skeptical
to
say the least. Still, I was curious. I figured I could stand to lose
six
bucks, so I kept reading.


I'm pretty glad I did. All you had to do was send $1.00 to the 6 names
at
the addresses listed in the article. Then, you placed your name and
address
at the bottom of the list at position #6, and posted the article to at
least
200 newsgroups.


I felt pretty silly after I'd sent the letters, and it took a bit of
time to
post the message to all those newsgroups. To be honest, I pretty much
forget about the whole deal there and then. "It's only six dollars. No
big
deal."


Was I in for a surprise. GUESS WHAT! Within 7 days, I started getting
money
in the mail! It was amazing! I figured it would end, but it didn't.
The
money just kept rolling in. I made about $18.00 in the first week. By
the
end of the second week I'd made a total of over $980. $10,328 in week
three, and it just went on and on. This is now my fifth month and I'm
sitting on about $273,000. Needless to say I quit my job a while back.
(I
used to work as a computer software manager)


It was certainly worth the $6.00 and change for the stamps. I've spent
more
than that on the lottery, without a cent to show for it!!


Print a copy of this article, so you can refer back to it, or cut and
paste
it to Notepad or Word. The process is very simple and is comprised of
3
easy steps. If you're wondering why I'm letting you in on this, I'll
explain it to you shortly. Bear with me. This works.


STEP 1: Get 6 separate sheets of paper and write the following on each;

"PLEASE PUT ME ON YOUR MAILING LIST."


Get 6 US$1.00 bills (or the equivalent in your local currency) and
place a
dollar and a note in each of the 6 envelopes. Fold the bill into the
paper
in order to prevent it from being seen, and possibly stolen.


You should now have 6 sealed envelopes, each containing a dollar and
the
note. Don't forget to add your name and address.


Mail the 6 envelopes to the following addresses:


#1 R. Arambasic, 9 Ashmore St, Brunswick, VIC, Australia 3056
#2 S. Vouge, P.O. Box 5173, New York, N.Y. 10163, USA
#3 R. Dumancic, Mlinarska 22A, Zagreb, 10000, Croatia
#4 D. Lozina, 128 Nicholson St, Fitzroy, VIC, Australia 3065
#5 B. Spaleta, 39 Stewart Gve, Campbellfield, VIC, Australia 3061
#6 J. Wurdemann, P.O. Box 912, North Branch, MN. 55056, USA


STEP 2: Take name #1 off the list above, move the other names up (6
becomes
5, 5 becomes 4, etc...) and add YOUR name as number 6 on the list.
STEP 3: Post your amended article to at least 200 newsgroups. (There's
heaps
out there) All you need is 200, but the more you post, the more money
you
make!


********* HOW TO POST TO NEWSGROUPS (It's easy) *********


1. You don't need to re-type this entire letter to do your own posting.
Cut
and paste this letter to your Notepad. 2. Remember to eliminate the #1

position, move everyone up a spot (re-number everyone else's
positions),
and add yourself as #6. 3. Save your new notepad file as a .txt file.
If
you want to do your postings in different sittings, you'll always have
this
file to go back to.


*** NETSCAPE USERS ***


Step 4. Within the Netscape program, go to the pull down window
entitled
'Window' select 'NetscapeNews'. Then from the pull down menu
'Options',
select 'Show all Newsgroups'. After a few moments a list of all the
Newsgroups on your server will show up. Click on any newsgroup you
desire.
From within this newsgroup, click on the 'TO NEWS' button, which should
be
in the top left corner of the newsgroups page. This will bring up a
message
box.


Step 5. Fill in the Subject. This will be the header that everyone sees
as
they scroll through the list of postings in a particular group.


Step 6. Highlight the entire contents of your .txt file, and cut and
paste
it the letter into the body of your posting.


Step 7. Hit the 'Send' Button in the upper left corner. You're done
with your
first post! Congratulations...


*** INTERNET EXPLORER USERS ***


Step 4. Go to newsgroups and select 'Post an Article'.
Step 5. Fill in the subject.
Step 6. Same as #6 above
Step 7. Hit the 'Post' button.


Alternatively, you can use a program like Forte Agent, which you can
find on
the Web.


THAT'S IT! All you have to do is jump to different newsgroups and post
away,
after you get the hang of it. It takes about 30 seconds for each
newsgroup!


**REMEMBER, THE MORE NEWSGROUPS YOU POST TO, THE MORE MONEY YOU'LL
MAKE!!
POST A MINIMUM OF 200**


There you go! You'll begin receiving money from around the world
within
days! You may eventually even want to rent a P.O. Box due to the large

amount of mail you'll receive. Should you wish to stay anonymous, you
may
use a pseudonym, as the postman will deliver it just the same.


**MAKE SURE ALL THE ADDRESSES ARE CORRECT.**


So, why am I letting you in on this. Let me explain.


Out of 200 postings, say I receive only 5 replies. I make $5.00 with
my
name at #6 on the letter. Now, if each of the 5 individuals who sent
me
$1.00 make the minimum 200 postings, with my name at #5, and only 5
people
respond to each of the original 5, that's another $25.00 for me. Now
those
25 each make 200 posts with my name at #4, and with 5 replies each, I
earn
an additional $125.00! Those 125 turn around and post the minimum 200
with
my name at #3 and receive 5 replies each, I make $626.00 more! Get the
picture? Five responses is actually a below norm response rate. The
average is about 15 to 25. For example, here's what you can expect to
earn from 15 responses:


at #6 $15.00 at #5 $225.00 at #4 $3,375.00 at #3 $50,625.00 at
#2
$759,375.00 at #1 $11,390,625.00


When your name is no longer on the list, you just take the latest
posting in
the newsgroups, and send out your $6.00 to names on the list, putting
your
name at number 6 again (which is what I'm doing), and start posting
again.


The thing to remember is that thousands of people all over the world
are
joining the internet and reading these articles everyday, just as you
are
now!!


Can you afford $6.00? I believe so. (I just didn't buy lunch that day)



People have said, "what if the plan is played out and no one sends you
the
money? Doesn't matter. There are tons of new honest users and new
honest
people who are joining the internet and newsgroups everyday, willing to
give
it a try? Estimates are at 20,000 to 50,000 new users daily.


This will work for you. Be honest, be fair. Remember, what goes around

comes around.

Paul Rubin wrote:
I had a picture that was slightly off-vertical. To put it on the web
I wanted to first rotate it by a few degrees, then resize it to web
resolution (about 0.3x). I used GIMP and selected bicubic
interpolation for both transforms and the result still came out a
little bit blurry. I'm wondering if the interpolations (which by
definition computes each destination pixel from several source pixels)
get worse as they are compounded. Maybe photo editors should keep
track of these transformations as you do them on-screen, and combine
them into a single transformation matrix (or different matrices for
different regions of the picture as you cut and paste). Then at the
end you'd re-transform the picture (i.e. go from the initial to final
picture) in a single pass, without all the intermediate steps. In
that way you'd only be interpolating once instead of several times.

Do any editing programs do that? Is there a way to get GIMP to do it?
Does it make sense?
In most cases, it is better to crop than rotate as cropping will not
markedly degrade the image, just discards a few pixels.

Paul Rubin wrote:
I had a picture that was slightly off-vertical. To put it on the web
I wanted to first rotate it by a few degrees, then resize it to web
resolution (about 0.3x). I used GIMP and selected bicubic
interpolation for both transforms and the result still came out a
little bit blurry.

Since it is downsized a lot, 3x, the rotate degrading should be
neglectable. The blurry probably resulted from the bicubic resampling.

I'm wondering if the interpolations (which by
definition computes each destination pixel from several source pixels)
get worse as they are compounded. Maybe photo editors should keep
track of these transformations as you do them on-screen, and combine
them into a single transformation matrix (or different matrices for
different regions of the picture as you cut and paste). Then at the
end you'd re-transform the picture (i.e. go from the initial to final
picture) in a single pass, without all the intermediate steps. In
that way you'd only be interpolating once instead of several times.

Do any editing programs do that?

Photoshop layers are supposed to work this way. Every editing is in a
separate layer. You collapse the layers to get the end result.

I am not sure whether these particular editings can be layers in the
latest version of Photoshop.

http://digitcamera.tripod.com/#slr

wrote:
Paul Rubin wrote:
I had a picture that was slightly off-vertical. To put it on the web
I wanted to first rotate it by a few degrees, then resize it to web
resolution (about 0.3x). I used GIMP and selected bicubic
interpolation for both transforms and the result still came out a
little bit blurry.

Since it is downsized a lot, 3x, the rotate degrading should be
neglectable. The blurry probably resulted from the bicubic resampling.

I'm wondering if the interpolations (which by
definition computes each destination pixel from several source pixels)
get worse as they are compounded. Maybe photo editors should keep
track of these transformations as you do them on-screen, and combine
them into a single transformation matrix (or different matrices for
different regions of the picture as you cut and paste). Then at the
end you'd re-transform the picture (i.e. go from the initial to final
picture) in a single pass, without all the intermediate steps. In
that way you'd only be interpolating once instead of several times.

Do any editing programs do that?

Photoshop layers are supposed to work this way. Every editing is in a
separate layer. You collapse the layers to get the end result.

I am not sure whether these particular editings can be layers in the
latest version of Photoshop.

http://digitcamera.tripod.com/#slr

Irfanview has a somewhat more sophisticated Lanczos filter
for doing shrinking. It uses more points and, I think, can
detect sharp edges. I've used it and like it.

Since Irfanview is free, why not give it a try?

----- Paul J. Gans