Re: Resolution of graphics for printed docs

Subject: Re: Resolution of graphics for printed docs
From: Bill Swallow <techcommdood -at- gmail -dot- com>
To: "TECHWR-L" <techwr-l -at- lists -dot- techwr-l -dot- com>
Date: Wed, 5 Oct 2005 14:05:30 -0400

> A 72 ppi image means there's 72 pixels per inch.

That is correct.

> So with a 504-pixel-wide
> image, if you divide 504 by 72, you get 7 inches, which is how Photoshop
> comes up with that value.

Correct, if you're planning to output at 72 ppi, then yes, it's 7 inches wide.

> Now here's the important bit: Photoshop calls
> this the "Print size" because that's the size it will be output from a
> printer.

You're absolutely right, if you don't adjust the ppi value that's the
"print size".

> You don't have to believe me, just print out a web page and see
> how it fills the page (unless you've set a reduction percentage).

I think you're missing a fundamental point, and that is that ppi is an
arbitrary value assigned to an image for output and has no hard impact
on the physical size or quality of an electronic image.

> Crude as in a printed 72-ppi image looks huge, and photos printed at that
> resolution have compression artifacts that make the images look blurry.

Well, now you're mixing fruit, and again you're missing the
fundamental point that ppi is a scalability value for printed output
and nothing more. If you want a smaller image, increase the ppi.
Unless you have all of Photoshop's nasty little constraints tied
together, adjusting ppi in Photoshop will not increase file size,
increase physical size, or otherwise distort the original file. It's
just a numeric data point in the image file's metadata.

> If you double the ppi with resampling turned on in Photoshop, the file
> size doubles. If you do the same with no resampling the file size stays
> the same, but the image's print size is reduced by 50%.

Ahhh... you're actively choosing to turn on resampling... that's the
crux of your issue, then. Don't do that. It's not necessary for images
being used within DTP applications. Apps such as Word and FM use ppi
scaling to adjust image size, so resampling and physical resizing in
Photoshop or another image editor is unneccessary (and detrimental to
image integrity).

> That's enough, I think the rest of what I wrote in that post stands well
> enough.

For the benefit of the list, the information you have been posting is
incorrect. It might look OK to you, but it is in fact incorrect and is
suggesting that distorting images in a graphic-editing tool is the
ideal way of increasing image clarity, which couldn't be further from
the truth. Once you start adding or deleting pixels in your image, you
have distorted it, and there's no way to revert back to the original,
best clarity without reverting to a saved original copy of the image
before it was tweaked.

Bill Swallow
HATT List Owner
WWP-Users List Owner


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