Re: Another resize/image quality question

On Mon, 26 Dec 2005 17:19:44 GMT, tacit wrote:

> In article <13g426sms1hj3.oiva6340g1ik$.dlg@xxxxxxxxxx>,
> Jim Hargan <contactATharganonlineDOTcom@xxxxxxxxxx> wrote:
>
>> Be sure to tell your people to NOT use jpeg to capture the images. Use tiff
>> or raw. Jpeg damages resolution -- tiff and raw do not.
>
> JPEG does not damage *resolution*. That is a misunderstanding of JPEG
> compression.
>
> JPEG damages image information, and degrades image detail, but this
> process has nothing to do with resolution. A 300 pixel per inch image
> saved as JPEG is still 300 pixels per inch; the resolution is undamaged.
> However, the image is degraded because artifacts are introduced around
> sharp edges and areas of high contrast, and areas of solid color show
> patterns such as "blocking."

Yes, but ...

Jpeg reduces the information in order to simplify, and therefore shrink,
the image. Less information = blurrier print.

We may be making a verbal argument over "resolution". Here's a thought
experiment: Let's say I pick up a lightweight amateur 6 megapix camera,
hold it in my hands, and shoot an overcast landscape. Now I do the same
with an $8,000 pro 12 megapix model. Which picture has more "resolution"?

By your definition, the 12 megapix image will always have double the
resolution. *But* the 6 megapix camera is substantially lighter, and so my
hands would shake less during the long exposure. For this reason, my 6
megapix image would probably be sharper and more detailed than my 12
megapix image. This is what I meant when I used the term, "resolution".

I would call your concept, "maximum resolution" or "maximum resolving
power". To see the difference, imagine that I am taking the picture of a
resolution target instead of a cloudy landscape. My 'low resolution' 6
megapix image, with less shutter shake, would resolve a closer line pattern
than my 12 megapix image with more shutter shake.

True story: About 15+ years ago, two friends of mine went to London for a
week. One purchased a top of the line pro camera with a big zoom lens. The
other used a $75 point and shoot with a fixed lens and leaf shutter. The
sun never shown once, the entire week. Guess who had dramatically clearer
pictures? The point and shooter, of course.


--
Jim Hargan
Freelance Photographer and Writer
www.harganonline.com
.

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