Re: [APML] Photoshop image scaling; was: Dumb question time

["Bert Katzung" <katzung1@attbi.com>]

George, Matt, Jerry, and Scott:
A very interesting series of answers to George's question! Made me go back
to the drawing board and run some tests on some ordinary CCD and film
images. The ccd images were native ST-10 fit files (2184 x 1472 pixels) and
the film was regular 35 mm scanned at the max of my Polaroid 35+ (2700 or
2750). I assume we all agree that with resizing we can never add
information, we can only try to avoid losing information while making the
final result as pleasing as possible.

I cropped a small section of a CCD image and tried printing with no
resampling (72 ppi, resulting in a 4+ x 6+ inch image; 72 ppi is the native
Photoshop res for my fit images), resampling to 288 ppi (4x multiple of
native, same 4x6 size) and resampling to 300 ppi, same 4x6 size, and made a
print of each. Naked eye they all looked similar (except for text I had
added to the image at the original size). Under a 10x loupe I could see no
difference between the 288 and 300 ppi prints  but the 72 ppi print was
definitely coarser. I wasn't surprised by the latter result.

Matt, maybe I'm missing something, but unless I start with a resolution that
permits Photoshop's Scale to Fit Media to reach the paper dimensions without
dropping much below 200 to 300 ppi, I get a very blocky result. Example,
trying to enlarge a 1/3 crop of a 35 mm scan (2700 ppi, left with 900+
pixels) up to 8x10. On the other hand, if I resample, I avoid the blockiness
and visually the enlargement looks good.
There are some further extensions of this question in the ccd processing
arena, where up-sampling seems to be helpful, but that's a subject for
another list.
Bert

Bert Katzung
katzung1@attbi.com
www.astronomy-images.com

----- Original Message -----
From: "Matt BenDaniel" <matt@starmatt.com>
To: <astro-photo@seds.org>
Sent: Monday, December 09, 2002 10:49 PM
Subject: Re: [APML] Photoshop Dumb question time


> George,
>
> Do not resample your image in order to print. Keep the image at full
resolution.
>
> First use Photoshop Page Setup to set the page size and orientation.
>
> Then use Print Options and select Scale to Fit Media (or manually set the
height or width).
>
> Then print.
>
> Matt
>
> At 23:31 09-12-02 -0500, George Anderson wrote:
> >I finally have a printer capable of colour work (Epson photo 820).
> >When I print from photoshop and I resize the picture to fit the paper do
> >I reduce the pixels per inch to match the increase in size of the image
> >thus maintaining the number of pixels along the dimensions? Or do I
> >resize and set the number of pixels to match the resolution of the
> >printer and allow photoshop to interpolate the data (really big file)?
>
> --
> Matt BenDaniel
> matt@starmatt.com
> http://starmatt.com
>
>
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