Message-Id: <mailto:199507140258.VAA23207@library.wustl.edu> Date: Thu, 13 Jul 1995 23:03:12 -0400 From: S Merrell <mailto:jaxon@PANIX.COM> Subject: Re: Scan Bits cvs dpi To: Multiple recipients of list IMAGELIB
On Tue, 11 Jul 1995, Reid McCallister <mailto:MCCALLISTER@IGS.CVIOG.UGA.EDU> asked:> Would someone explain the relationship between bit depth and dpi.
I'll try.
Bit depth and DPI really aren't related at all.
Bit depth refers to the number of levels of gray (or color) available to define discrete (different) tones in digital images. More is better, usually... especially in a scanner. It's called bit depth because, in order for an image to have more levels of gray, more bits of data per pixel are required to carry the wider range of tone definitions.
DPI (dots per inch) refers to the number of image pixels being mapped into two dimensional space. A higher DPI value means that a given # of pixels are being packed together more tightly - to produce more apparent image sharpness. The DPI value by itself is useless unless you know the dimensions of the area being covered at that given DPI. The absolute number of pixels in an image is the REAL telltale of image resolution. Again, the more pixels, the higher the resolution. Any number of pixels can be "mapped" to any DPI value. So, image resolution is really a matter of how many square inches are being covered by how many pixels.
>>Is the
>higher dpi with less bit depth preferable.
Depends on what you're trying to do. Greater bit depth will usually provide better scans. Higher DPI will produce higher-resolution scans (assuming the scanning bed is the same size on both scanner models.
Hope this helps.
Sam Merrell________________________________________ Synthetic Imaging, Inc/NYC - 212.684.6311 mailto:76702.1252@compuserve.com mailto:jaxon@panix.com