[filmscanners] RE: Genuine fractals?????

["Jawed Ashraf" <Jawed@cupidity.force9.co.uk>]

Put simply, you're confused by the way that certain software applications
(e.g. Photoshop or scanner software such as Nikon View) allow the user to
specify the pixel-dimensions of a destination image by specifying dpi and
linear dimensions (in units that are not pixels - e.g. by requesting an 8
inch picture on the longest dimension, at 300dpi).  The fact that these
applications allow the user to avoid thinking in terms of the number of
pixels per side in an image does not in any way alter the fact that the
quality settings of a digital camera do not include manipulation of the dpi
setting.  

Digital cameras' size/resolution quality is only determined by file format
(JPEG, TIFF, RAW etc.) and pixel-dimensions.  JPEG usually has a sliding
scale of "quality" values that the photographer can select, compromising
picture quality against storage card capacity.  The digital photographer
cannot directly manipulate dpi in the camera, and even if it was possible it
would be meaningless, since the pixel-dimensions of the file are what
determine resolution.

If you examine the Image Size dialog in Photoshop you will discover that it
is possible to arbitrarily alter the dpi setting of a picture and in doing
so, the pixel-dimensions of the picture will not change.  It is merely a
question of asking Photoshop not to resample the picture whilst altering the
dpi setting.  

This is often a handy first step in performing a re-size in order to take a
source picture and transform it into the correct number of pixels to
print/show on a device at a given size.  Photoshop allows the photographer
the chance to perform this sizing operation without having to calculate the
pixel-dimensions of the destination image.  The second step is to re-open
the Image Size dialog and turn on Resample Image, and then enter the
dimensions in the desired units (e.g. 8 inches).

Jawed

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