[Gimp-user] problems with understand how to resize images properly

[Amira_Cervantes <forums gimpusers com>]

> Hi menglor,
>
> The process you describe will give you images of different sizes if
> the
> originals have different DPI values, because when you scale an image
> to
> be a certain number of inches in size, the GIMP looks at the DPI
> resolution of the image first, then scales the image to be X number of
> pixels wide/tall based on that DPI and the physical dimensions you
> specify.
>
> Example:  A 300 DPI image scaled to 1" x 1" will come out 300 pixels
> wide.  A 150 DPI image scaled to 1" x 1" will come out 150 pixels wide
> -
> half "size" of the 300 DPI one.
>
> Scaling images by adjusting their size in inches (or centimeters,
> etc.)
> is rarely done.  Useful results require resetting the DPI of images as
> necessary, so a set of images of the same size in inches, cm or etc.
> will also be the same size in pixels.
>
> Or can multiply the size in inches of the output images you want by
> the
> DPI you want, to get the correct dimensions in pixels for /all/ the
> images intended to be the same size when printed.  From that point on,
> you can just scale your whole batch of images to the same size in
> pixels
> and ignore the size "in inches."
>
> The DPI setting in an image is only a number recorded in the file
> header; changing the DPI of an image changes nothing but that one
> number, and as far as I know it does not affect the actual or
> displayed
> / printed size of the image, except when scaling the image in an
> editor
> like the GIMP.
>
> Typical DPI values:
>
> 300 DPI for high quality print
> 150 DPI for office documents etc. where "good enough is good enough"
> 96 DPI for on-screen display
> 72 DPI - a legacy default setting based on printers' "point" size
>
> Note that doubling the DPI of an image while maintaining the same
> print
> size when scaling, multiplies the size of the resulting file on disk
> by
> about 4x.  Exporting images in lossless PNG format (vs. lossy JPG) for
> maximum print quality also creates much larger file sizes on disk.  So
> big, high quality print jobs can take up a lot of space in storage or
> time in transit across the network.
>
> You also mentioned printing via a Word document, and that the sizes
> you
> get are a little off.  I think that's to be expected, because word
> processors were not intended for "pre-press" work, a.k.a. printing
> images with high accuracy.
>
> I use Scribus, a Free desktop publishing application, for pre-press
> work.  Make your images, put them on the page exactly where you want
> them, export the file as PDF and print that:  Viola, accurate results.
>
> For really precise positioning on page, i.e. when printing on peel and
> stick label stock or etc., it may be necessary to print a test page,
> measure any placement errors, and adjust the Scribus master document
> to
> get your required results from that particular printer.
>
> https://www.scribus.net/
>
> :o)




Thanks. Seems like learned some  new things today. :D

-- 
Amira_Cervantes (via www.gimpusers.com/forums)