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post #31 of (permalink) Old 04-26-2008, 07:48 AM
High on the Mountain Top
 
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The pixel size of the image is responsible for the file size (within a given file type), and it's the file size that slows things down. Smaller pixels = more pixels per image = bigger file.
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post #32 of (permalink) Old 05-01-2008, 12:01 PM
High on the Mountain Top
 
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Quote:
quote:Originally posted by magnetite

The pixel size of the image is responsible for the file size (within a given file type), and it's the file size that slows things down. Smaller pixels = more pixels per image = bigger file.
Pixels have no size. They are just a "dot" of colour. Their physical size is determined by what kind of monitor you use... If you print the image then the "pixel" size is determined by the printer resolution.

Right, files with lots of pixels are slow to manipulate because it takes # pixels * colour depth per pixel bits of memory to load them. When they are saved in files various compression schemes can of course make them much smaller.
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post #33 of (permalink) Old 05-01-2008, 01:59 PM
High on the Mountain Top
 
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Interest: Mountain biking, hiking, nature photography, astronomy, music...
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Quote:
quote:Originally posted by swebster

Quote:
quote:Originally posted by magnetite

The pixel size of the image is responsible for the file size (within a given file type), and it's the file size that slows things down. Smaller pixels = more pixels per image = bigger file.
Pixels have no size. They are just a "dot" of colour. Their physical size is determined by what kind of monitor you use... If you print the image then the "pixel" size is determined by the printer resolution.

Right, files with lots of pixels are slow to manipulate because it takes # pixels * colour depth per pixel bits of memory to load them. When they are saved in files various compression schemes can of course make them much smaller.
When talking about spatially referenced imagery (maps, orthophotos, satellite images etc), pixels do have a size. If a 1:50,000 scale map is scanned at 150 dpi, each pixel in the resulting image represents roughly 8.5 x 8.5 metres on the ground. You can figure this out using the formula P=(1/Scale) x (0.0254/dpi).
For example P = 50,000 x (0.0254/150) = 8.46 metres per pixel. In the mapping industry that's what we call pixel size.
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post #34 of (permalink) Old 05-01-2008, 02:11 PM
High on the Mountain Top
 
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Location: New Westminster, BC, Canada.
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Quote:
quote:Originally posted by magnetite
When talking about spatially referenced imagery (maps, orthophotos, satellite images etc), pixels do have a size. If a 1:50,000 scale map is scanned at 150 dpi, each pixel in the resulting image represents roughly 8.5 x 8.5 metres on the ground. You can figure this out using the formula P=(1/Scale) x (0.0254/dpi).
For example P = 50,000 x (0.0254/150) = 8.46 metres per pixel. In the mapping industry that's what we call pixel size.
Ahh, I see what you mean now.
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