Re: How does one obtain the resolution of an image in PHP?

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Hi!

On Thu, 16 Mar 2006 14:31:38 -0500
John Hinton <webmaster@xxxxxxxx> wrote:

> Simon M. Campden-Main wrote:
> >
> > Well, there's the meat of it, isn't it?  I wonder how Paint
> > Shop Pro comes up with PPI (Image - Image information). 
> > I have several thousand scanned images with resolution
> > ranging from 72 PPI up to 1200 PPI (As reported by Paint
> > Shop Pro) and want to discard, or more likely tag as
> > rejected, any that suffer a resolution of less than 150
> > PPI.  As you might imagine, I find the thought of
> > doing it manually with Paint Shop Pro repugnant.

Okay, if it was scanned at 72ppi then you can't really print
it out again even with a near-similar quality. However, having
an image with a 72ppi does NOT necessarily mean that you
have an image unsuitable for printing.

> PPI or pixels per inch is a printing term.

Last time I checked, "dpi" is the printing term. (^_^)

  dpi (dots per inch) -> printer
  ppi (pixels per inch) -> monitor/screen

> It has nothing to do with viewing on a monitor as a 
> monitor's pixel setting is your set resolution, as in
> 800x600, 1024x768, 1600x1200.. etc. This is a 
> constantly debated urban legend. A pixel on a monitor
> is a pixel...

True.

> Pixels per inch are used in the printing world and relates to
> how many pixels are used to provide one inch of printed
> space. Obviously, at least up to the limits of the printer
> being used, a high PPI setting produces a higher quality
> 'printed' image.

This really depends on how big the image is to be printed.
Besides, an image/photo taken using a digital camera (at
least mine) always defaults to 72ppi. BUT that does not
mean that it will come out badly printed at 300 dpi -- it
all depends on how big is the size (setting) of the picture
when I first took it.

> If you don't believe me, use your paint program, change the
> PPI of an image and notice how the image doesn't change size
> on the screen. Also, do this and switch the image size
> display back and forth between inches and pixels.. the pixel
> count doesn't change, only the inches change.. but again...
> that's the printing world and has nothing to do with display
> on a monitor or webbrowser.

True. This is basically because most monitors/screens are
actually at or near 72 ppi. "screen" !== "printer" (^_-)

> So, an image 10,000pixels by 10,000pixels will be huge on
> screen. If set to a resolution of 1000ppi, the image would be
> printed at 10" x 10", but you still can't view the whole
> image on a monitor without zooming out. If resolution we set
> to 10,000dpi, the image would print as 1" x 1", but you still
> wouldn't be able to view it on a monitor (unless you have an

I think you meant, "... but you still would be able ... "

> awesome multi-display setup that can reach 10,000 pixels wide
> and tall). That's the bottom line.
> 
> So, I keep seeing 'display size' when I'm thinking the term
> should be 'printed size'.
> 
> John Hinton

HTH & HAND,

- Edwin -

-- 
"A capable wife is a crown to her owner." - Proverbs 12:4

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