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2 Pics Scanned @ width 1024 pixels, and DPI 72 and 300. What Is the Photographic Quality Difference?

 
 
Ubiquitous
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      12-23-2003

"Comancheros >" <<> wrote in message
news:(E-Mail Removed)...
> I have an Epson Expression 636 scanner. I scan
> an image at 72 dpi and then at 300 dpi. I keep the
> width to 1024. What is the actual photographic quality difference
> between the 2 pictures? Again, the pictures are scanned at width 1024
> pixels. They are NOT ENLARGED/CROPPED to 1024 pixels after the
> scanning.
> Thank you!


That doesn't really make a lot of sense, but I would have to assume that if
you scanned something and forced the width to be 1024 pixels wide, the one
scanned at 300 dpi would be a crop of the one scanned at 72 dpi due to more
pixels being scanned in for a given area. (in this case, approximately 3
inches). The one scanned in at 72 dpi would cover an area of approximately
13 inches.


 
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Jim Townsend
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      12-23-2003
Comancheros <<>> wrote:

> I have an Epson Expression 636 scanner. I scan
> an image at 72 dpi and then at 300 dpi. I keep the
> width to 1024.


?? How can you scan the same sized image at different resolutions and have the
same amount of pixels ??

dpi is 'dots per inch'. The dots are the samples and the inch is the physical
size of the document you are scanning.

If you have a 1 inch wide document and scan it at 300 dpi, you get an image
that's 300 pixels wide. If you scan a 1 inch wide document at 72 dpi, you get
an image that's 72 pixels across. A 2 inch image scanned at 72 dpi will be
2x72=144 pixels. It's simple math.

What size is the document you are scanning and how are you arriving at 1024 ?


> What is the actual photographic quality difference
> between the 2 pictures? Again, the pictures are scanned at width 1024
> pixels. They are NOT ENLARGED/CROPPED to 1024 pixels after the
> scanning.
> Thank you!
>
> phaethon


 
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Comancheros
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      12-23-2003
I have an Epson Expression 636 scanner. I scan
an image at 72 dpi and then at 300 dpi. I keep the
width to 1024. What is the actual photographic quality difference
between the 2 pictures? Again, the pictures are scanned at width 1024
pixels. They are NOT ENLARGED/CROPPED to 1024 pixels after the
scanning.
Thank you!

phaethon

 
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Christian
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      12-23-2003
Comancheros <<>> wrote:

> I have an Epson Expression 636 scanner. I scan
> an image at 72 dpi and then at 300 dpi. I keep the
> width to 1024. What is the actual photographic quality difference
> between the 2 pictures? Again, the pictures are scanned at width 1024
> pixels. They are NOT ENLARGED/CROPPED to 1024 pixels after the
> scanning.


As others have said, this isn't possible. When people talk about dpi/ppi
(different but similar enough for this discussion) this refers to an input
or output resolution. Digital images have no actual size other than their
"resolution" meaning the number of pixels on the x and y axes (i.e.,
1024x76. A pixel has no actual size, it's just a discrete dot. However,
when people talk about the "resolution" of scanners/printers/monitors
(i.e., input and output devices) and start talking about dpi/ppi then what
they are really saying is the density of those pixels. In the case of a
scanner it is how many pixels are formed in the digital image being
generated from a fixed size of the print etc. being scanned. So if you
scan at 300 dpi you get a lot more pixels (and thus a bigger, higher
quality image) than if you scan at 72 dpi. When it comes to printers and
monitors then a similar thing applies. You are taking the digital image
(which has no actual size, just x and y dimensions) and placing those
pixels on the page/screen at a given spacing. The most confusing thing
about this is that many image formats allow you to specify the output
resolution of the digital file in dpi. But this doesn't change the
inherent size or photographic quality of the image (all the same pixels are
still there), it just affects it when the image is output.
 
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BF
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      12-23-2003
The problem is people interchange and just don't understand the
difference between DPI (dots per inch), PPI (pixels per inch), scanner
resolution and printer resolution. It is not difficult to understand
once you sort it all out. It took me a long time to figure out that
most people were mixing the terms together, which is very confusing.
Printer DPI has nothing to do with scanner DPI. Printer PPI only has
to do with the size of the printed image.



"Christian" <(E-Mail Removed)> wrote in message
news:bs8dl6$6iq$(E-Mail Removed)...
> Comancheros <<>> wrote:
>
> > I have an Epson Expression 636 scanner. I scan
> > an image at 72 dpi and then at 300 dpi. I keep the
> > width to 1024. What is the actual photographic quality difference
> > between the 2 pictures? Again, the pictures are scanned at width

1024
> > pixels. They are NOT ENLARGED/CROPPED to 1024 pixels after the
> > scanning.

>
> As others have said, this isn't possible. When people talk about

dpi/ppi
> (different but similar enough for this discussion) this refers to an

input
> or output resolution. Digital images have no actual size other than

their
> "resolution" meaning the number of pixels on the x and y axes (i.e.,
> 1024x76. A pixel has no actual size, it's just a discrete dot.

However,
> when people talk about the "resolution" of

scanners/printers/monitors
> (i.e., input and output devices) and start talking about dpi/ppi

then what
> they are really saying is the density of those pixels. In the case

of a
> scanner it is how many pixels are formed in the digital image being
> generated from a fixed size of the print etc. being scanned. So if

you
> scan at 300 dpi you get a lot more pixels (and thus a bigger, higher
> quality image) than if you scan at 72 dpi. When it comes to

printers and
> monitors then a similar thing applies. You are taking the digital

image
> (which has no actual size, just x and y dimensions) and placing

those
> pixels on the page/screen at a given spacing. The most confusing

thing
> about this is that many image formats allow you to specify the

output
> resolution of the digital file in dpi. But this doesn't change the
> inherent size or photographic quality of the image (all the same

pixels are
> still there), it just affects it when the image is output.



 
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hydra
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      12-23-2003
On Mon, 22 Dec 2003 20:05:27 -0600, Jim Townsend <(E-Mail Removed)>
wrote:

>Comancheros <<>> wrote:
>
>> I have an Epson Expression 636 scanner. I scan
>> an image at 72 dpi and then at 300 dpi. I keep the
>> width to 1024.

>
>?? How can you scan the same sized image at different resolutions and have the
>same amount of pixels ??
>
>dpi is 'dots per inch'. The dots are the samples and the inch is the physical
>size of the document you are scanning.
>
>If you have a 1 inch wide document and scan it at 300 dpi, you get an image
>that's 300 pixels wide. If you scan a 1 inch wide document at 72 dpi, you get
>an image that's 72 pixels across. A 2 inch image scanned at 72 dpi will be
>2x72=144 pixels. It's simple math.
>
>What size is the document you are scanning and how are you arriving at 1024 ?
>
>
>> What is the actual photographic quality difference
>> between the 2 pictures? Again, the pictures are scanned at width 1024
>> pixels. They are NOT ENLARGED/CROPPED to 1024 pixels after the
>> scanning.
>> Thank you!
>>
>> phaethon



 
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hydra
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      12-23-2003
On Mon, 22 Dec 2003 20:05:27 -0600, Jim Townsend <(E-Mail Removed)>
wrote:

>Comancheros <<>> wrote:
>
>> I have an Epson Expression 636 scanner. I scan
>> an image at 72 dpi and then at 300 dpi. I keep the
>> width to 1024.

>
>?? How can you scan the same sized image at different resolutions and have the
>same amount of pixels ??
>
>dpi is 'dots per inch'. The dots are the samples and the inch is the physical
>size of the document you are scanning.
>
>If you have a 1 inch wide document and scan it at 300 dpi, you get an image
>that's 300 pixels wide. If you scan a 1 inch wide document at 72 dpi, you get
>an image that's 72 pixels across. A 2 inch image scanned at 72 dpi will be
>2x72=144 pixels. It's simple math.
>
>What size is the document you are scanning and how are you arriving at 1024 ?
>
>
>> What is the actual photographic quality difference
>> between the 2 pictures? Again, the pictures are scanned at width 1024
>> pixels. They are NOT ENLARGED/CROPPED to 1024 pixels after the
>> scanning.
>> Thank you!
>>
>> phaethon


Jim,

1024 is a power of 2 and a possible HIRES horizontal screen dimension.
The scanner scales the picture to 1024 automatically, or to something
very close to 1024, and gives it to you back in 300dpi. This is what
the epson Expression 636 does if you first save it as a .ORG file
and then change the name to a .BMP one. You can do it for any
resolution all the way up to 4800dpi. My original question
is still valid and has gotten no answer whatsoever.

 
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hydra
Guest
Posts: n/a
 
      12-23-2003
On Mon, 22 Dec 2003 20:05:27 -0600, Jim Townsend <(E-Mail Removed)>
wrote:

>Comancheros <<>> wrote:
>
>> I have an Epson Expression 636 scanner. I scan
>> an image at 72 dpi and then at 300 dpi. I keep the
>> width to 1024.

>
>?? How can you scan the same sized image at different resolutions and have the
>same amount of pixels ??
>
>dpi is 'dots per inch'. The dots are the samples and the inch is the physical
>size of the document you are scanning.
>
>If you have a 1 inch wide document and scan it at 300 dpi, you get an image
>that's 300 pixels wide. If you scan a 1 inch wide document at 72 dpi, you get
>an image that's 72 pixels across. A 2 inch image scanned at 72 dpi will be
>2x72=144 pixels. It's simple math.
>
>What size is the document you are scanning and how are you arriving at 1024 ?
>
>
>> What is the actual photographic quality difference
>> between the 2 pictures? Again, the pictures are scanned at width 1024
>> pixels. They are NOT ENLARGED/CROPPED to 1024 pixels after the
>> scanning.
>> Thank you!
>>
>> phaethon


Jim,

1024 is a power of 2 and a possible HIRES horizontal screen dimension.
The scanner scales the picture to 1024 automatically, or to something
very close to 1024, and gives it to you back in 300dpi. This is what
the epson Expression 636 does if you first save it as a .ORG file
and then change the name to a .BMP one. You can do it for any
resolution all the way up to 4800dpi. My original question
is still valid and has gotten no answer whatsoever.

 
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Jim Townsend
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Posts: n/a
 
      12-24-2003
hydra <> wrote:


> Jim,
>
> 1024 is a power of 2 and a possible HIRES horizontal screen dimension.
> The scanner scales the picture to 1024 automatically, or to something
> very close to 1024, and gives it to you back in 300dpi. This is what
> the epson Expression 636 does if you first save it as a .ORG file
> and then change the name to a .BMP one. You can do it for any
> resolution all the way up to 4800dpi. My original question
> is still valid and has gotten no answer whatsoever.


Your scanner scales the picture to 1024 and gives it back at 300dpi if you save
it as an .ORG file then convert it to a .BMP ???

Now I see.. It appears you're very lost

Try this site.. It goes into scanning in *great* detail and should provide
answers your questions..

http://www.scantips.com/basics01.html


 
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