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Mr.Will 10-22-2003 02:53 AM

resampling a digital image to make it bigger?
 
Recently I was asked to print several of my shots at a 10 x 8 size, and to
crop quite heavily (about a quarter of the original frame). I took this
image with a Canon d60, and was concerned about noise and pixellation etc.
The day after that I saw the same photograph on the cover of a UK paper
blown up even bigger - and without pixellation or any noise! I was surprised
to say the least.

I had always thought that all images should be printed at 300dpi - so if one
wanted a bigger image than the frame, a loss in DPI would be neccessary. Not
so according to the people at the press, they merely resampled it in
photoshop.

I tried this instantly with the picture I had been asked for, and indeed it
worked out very nicely at 10 x 8. I simply resampled and kept the resolution
at 300dpi. What I dont understand is, what has the computer and photoshop
done to actually create more "pixels" for want of a better term?

--
Mr.Will



Bob Hatch 10-22-2003 03:02 AM

Re: resampling a digital image to make it bigger?
 

"Mr.Will" <mr.will@ntlworld.com> wrote in message
news:fkmlb.1354$Sb2.317@newsfep3-gui.server.ntli.net...

>
> I tried this instantly with the picture I had been asked for, and indeed

it
> worked out very nicely at 10 x 8. I simply resampled and kept the

resolution
> at 300dpi. What I dont understand is, what has the computer and photoshop
> done to actually create more "pixels" for want of a better term?
>
> --

Yes, and you can print at 250 PPI and you'll never see the difference
between that and 300. Our pro lab wants all images at size at 250 PPI. I
print at 250 PPI on my Epson 7600.

You know by now that your computer did not blow up and by using these extra
pixels you have not created a warp in the fabric of the universe. :-)

--
"Your money does not cause my poverty. Refusal to believe
this is at the bottom of most bad economic thinking." --P. J. O'Rourke
http://www.bobhatch.com



MikeWhy 10-22-2003 05:48 AM

Re: resampling a digital image to make it bigger?
 
"Mr.Will" <mr.will@ntlworld.com> wrote in message
news:fkmlb.1354$Sb2.317@newsfep3-gui.server.ntli.net...
> I tried this instantly with the picture I had been asked for, and indeed

it
> worked out very nicely at 10 x 8. I simply resampled and kept the

resolution
> at 300dpi. What I dont understand is, what has the computer and photoshop
> done to actually create more "pixels" for want of a better term?


I have heard, but have not actually confirmed, that enlarging by repeated
steps of 110% each time is better than a single large blow-up. FWIW. Maybe
it's something to do with Photoshop's bicubic interpolation, but I don't
know any details.


Robert E. Williams 10-22-2003 05:53 AM

Re: resampling a digital image to make it bigger?
 



"Mr.Will" wrote:

> Recently I was asked to print several of my shots at a 10 x 8 size, and to
> crop quite heavily (about a quarter of the original frame). I took this
> image with a Canon d60, and was concerned about noise and pixellation etc.
> The day after that I saw the same photograph on the cover of a UK paper
> blown up even bigger - and without pixellation or any noise! I was surprised
> to say the least.
>
> I had always thought that all images should be printed at 300dpi - so if one
> wanted a bigger image than the frame, a loss in DPI would be neccessary. Not
> so according to the people at the press, they merely resampled it in
> photoshop.
>
> I tried this instantly with the picture I had been asked for, and indeed it
> worked out very nicely at 10 x 8. I simply resampled and kept the resolution
> at 300dpi. What I dont understand is, what has the computer and photoshop
> done to actually create more "pixels" for want of a better term?
>
> --
> Mr.Will


To create new pixels, PS invents them. But it does so in an intelligent manner.
Its bicubic resampling algorithm looks at every pixel as well its nearest
neighbor and their nearest neighbors......etc.
It then creates new pixels that that blend best with all the other pixels in
the neighborhood.
This helps to make the images look smooth rather than pixelated at high
enlargements.

The 300 pixels/inch (ppi) criterion is for making prints indistinguishable from
traditional wet chemical prints.
High quality Art Magazines may also request 300 dpi ( really ppi).
I usually try to print at 240 uninterpolated ppi. If I don't have enough native
pixels in my image to print at 240 ppi, I'll have PS invent them. At other
times I'll just print at 200 ppi and get very good results
Newspapers are such low resolution media, that they can get by with 100 ppi, or
less.
Bob Williams


Fraser Wright 10-22-2003 10:38 AM

Re: resampling a digital image to make it bigger?
 
On Wed, 22 Oct 2003, MikeWhy wrote:

> "Mr.Will" <mr.will@ntlworld.com> wrote in message
> news:fkmlb.1354$Sb2.317@newsfep3-gui.server.ntli.net...
> > I tried this instantly with the picture I had been asked for, and indeed

> it
> > worked out very nicely at 10 x 8. I simply resampled and kept the

> resolution
> > at 300dpi. What I dont understand is, what has the computer and photoshop
> > done to actually create more "pixels" for want of a better term?

>
> I have heard, but have not actually confirmed, that enlarging by repeated
> steps of 110% each time is better than a single large blow-up. FWIW. Maybe
> it's something to do with Photoshop's bicubic interpolation, but I don't
> know any details.
>
>


To me it would seem that doing it many small step would be bad for exactly
the same reason photocopying photocopies of photcopies is bad.

Things don't get better as you interpolate on top of interpolation.

Xiaoding 10-22-2003 12:21 PM

Re: resampling a digital image to make it bigger?
 
>
> The 300 pixels/inch (ppi) criterion is for making prints indistinguishable from
> traditional wet chemical prints."



GASP! Surley you jest! INDISTINGUISHABLE? I think not! 300 crappy
pixels per inch does not make a Cibachrome print, sir. Please!!

HRosita 10-22-2003 12:51 PM

Re: resampling a digital image to make it bigger?
 
Hi,

There are additional algorithms for resampling. I use Genuine Fractals )a
Photoshop plugin).
Irfan view uses Lanczos.

Whatever you can always experiment and do your own evaluation at which one is
best.
Rosita



Bart van der Wolf 10-22-2003 12:53 PM

Re: resampling a digital image to make it bigger?
 

"Fraser Wright" <s358801@student.uq.edu.au> wrote in message
news:Pine.OSF.4.58.0310222034460.25588@student.uq. edu.au...
SNIP
> To me it would seem that doing it many small step would be bad
> for exactly the same reason photocopying photocopies of
> photcopies is bad.


That would intuitively seem what to expect, degradation with each next
generation. However, it's different with Bi-Cubic interpolation.

> Things don't get better as you interpolate on top of interpolation.


In a way they don't. However, when you interpolate/resize to a larger
dimension, Photoshop can add a little edge contrast at sharp brightness
transitions, depending on the surrounding pixels. Typically, edges (which
are most important for our impression of sharpness) will thus gain some
contrast. When repeated, this results in (visually) better (but slightly
exaggerated) edge contrast and less pixellation with extreme enlargements.
It offers a benefit over one step resampling which averages the edge
transitions but exaggerates individual pixel edges.

Bart



Mike Brodbelt 10-22-2003 01:34 PM

Re: resampling a digital image to make it bigger?
 
On Wed, 22 Oct 2003 05:48:04 +0000, MikeWhy wrote:

> "Mr.Will" <mr.will@ntlworld.com> wrote in message
> news:fkmlb.1354$Sb2.317@newsfep3-gui.server.ntli.net...
>> I tried this instantly with the picture I had been asked for, and indeed

> it
>> worked out very nicely at 10 x 8. I simply resampled and kept the

> resolution
>> at 300dpi. What I dont understand is, what has the computer and
>> photoshop done to actually create more "pixels" for want of a better
>> term?

>
> I have heard, but have not actually confirmed, that enlarging by repeated
> steps of 110% each time is better than a single large blow-up. FWIW. Maybe
> it's something to do with Photoshop's bicubic interpolation, but I don't
> know any details.


AFAIK, Lanczos interpolation is considered to be the best available
interpolation method by those who are supposed to know about such things.
Photoshop doesn't do Lanczos, but ImageMagick (which is free) does. I'd be
interested to see a comparison of the two sometime, and to know whether
the difference in quality between the algorithms is visible.

Mike.

/\\BratMan/\\ 10-22-2003 02:59 PM

Re: resampling a digital image to make it bigger?
 

"Mr.Will" <mr.will@ntlworld.com> wrote in message
news:fkmlb.1354$Sb2.317@newsfep3-gui.server.ntli.net...
> Recently I was asked to print several of my shots at a 10 x 8 size, and to
> crop quite heavily (about a quarter of the original frame). I took this
> image with a Canon d60, and was concerned about noise and pixellation etc.
> The day after that I saw the same photograph on the cover of a UK paper
> blown up even bigger - and without pixellation or any noise! I was

surprised
> to say the least.
>
> I had always thought that all images should be printed at 300dpi - so if

one
> wanted a bigger image than the frame, a loss in DPI would be neccessary.

Not
> so according to the people at the press, they merely resampled it in
> photoshop.
>
> I tried this instantly with the picture I had been asked for, and indeed

it
> worked out very nicely at 10 x 8. I simply resampled and kept the

resolution
> at 300dpi. What I dont understand is, what has the computer and photoshop
> done to actually create more "pixels" for want of a better term?
>
> --
> Mr.Will
>
>

Make a Photoshop Action to do it for you!


Open an image you want res up.

Open the Actions palette and select "New Set".

Name it "Creeping Increase" or whatever you like.

Now select New Action and call it "1.5 Increase"

Next go to Image/Size and put a check in "Resample" and "Constrain
Proportions"

with Bicubic and change the width drop down to "percent" and enter 110.

Now go to "Image Size" do the same 3 more times.

Then "Stop Recording"



Next "New Action" Name it "2.0 Increase"

Now "Edit/Purge All"

Next select the "1.5 Increase" in the Actions Palette

and press the Play button.

select the "1.5 Increase" again,

press the Play button again.

Stop Recording.



"New Action" Name it 3.0 Increase.

"Edit/Purge All"

Select and play the "2.0 Increase"

Select and play the "1.5 Increase"

Stop Recording.



"New Action" Name it 4.0 Increase.

"Edit/Purge All"

Select and play the "3.0 Increase"

Now "Image Size" 110 percent.

And again "Image Size" 110 percent.

Stop Recording.



Save the Action.




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