down resizing

T
Posted By
Tim923
Sep 25, 2004
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322
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7
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Does down resizing to 50% (1/2) make a better picture than fractions not based on multiples of 1/2?

http://mysite.verizon.net/vze8adrh/ –Tim923
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down resize

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Mike Russell
Sep 26, 2004
Tim923 wrote:
Does down resizing to 50% (1/2) make a better picture than fractions not based on multiples of 1/2?

http://mysite.verizon.net/vze8adrh/ –Tim923

The short answer is no. Provided have specified Bicubic resize in your prefs, the mathmatics PhotoShop uses generally work well at any fractional multiple of the original size. The exceptions are artificially generated images, such as line art, and, more rarely, photographs with certain patterns in them.

Standard operating procedure after a resize is to to do an unsharp mask operation to restore the sharpness every so slightly. This is generally done as a last step, or at least when the image is at its final viewing size.
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Mike Russell
www.curvemeister.com
www.geigy.2y.net
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Tim923
Sep 26, 2004
It seems that sometimes when Internet Explorer downsizes JPEGs to fit on the screen, the facial expression seems different.

http://mysite.verizon.net/vze8adrh/ –Tim923
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bagal
Sep 26, 2004
Similar effect on PDAs too

but I suppose there has to be a loss somewhere along the line as a consequence of digital image processing

Unlike light driven effect us using lenses to squish or enlarge an image digital images use algorithms to invent or guess new pixel values (enlarging) or may even ditch particular pixels when downsizing an image

Guessing: if a component in an image has (say) 16 pixels in one row – then reducing the image to half size MAY ditch half the pixels

Maybe a smarted algorithm could work along the lines of: what is the best way to optimise image fidelity during a downsize? (I guess the answer may be to convert it to another JPEG file of reduced image size?)

Artie

ps – my intuition is that it is digital component loss – a feature that may not be apparent when using lenses to resize images

A

"Tim923" wrote in message
It seems that sometimes when Internet Explorer downsizes JPEGs to fit on the screen, the facial expression seems different.

http://mysite.verizon.net/vze8adrh/ –Tim923
EG
Eric Gill
Sep 26, 2004
Tim923 wrote in
news::

It seems that sometimes when Internet Explorer downsizes JPEGs to fit on the screen, the facial expression seems different.

I’d imagine, since it simply squashes the image instead of actually resampling it.

What does this have to do with Photoshop?
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Tim923
Sep 26, 2004
What does this have to do with Photoshop?

I was concerned that if I downsized a JPEG in Photoshop, I would get similar distortions as with Internet Explorer if I didn’t use certain nice fractions like 1/2, 1/4.

http://mysite.verizon.net/vze8adrh/ –Tim923
EG
Eric Gill
Sep 27, 2004
Tim923 wrote in
news::

What does this have to do with Photoshop?

I was concerned that if I downsized a JPEG in Photoshop, I would get similar distortions as with Internet Explorer if I didn’t use certain nice fractions like 1/2, 1/4.

Good god- why?
B
bagal
Oct 3, 2004
I suppose there is a general image processing point though

Discrete math and all that. I expect the algorithms cater very well for resizing of non-integer multiples, divisors and all that

A good question perhaps?

I bet it was sorted in PS verion 1 or 2?

Arty

"Eric Gill" wrote in message
Tim923 wrote in
news::

What does this have to do with Photoshop?

I was concerned that if I downsized a JPEG in Photoshop, I would get similar distortions as with Internet Explorer if I didn’t use certain nice fractions like 1/2, 1/4.

Good god- why?

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