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

Discussion in 'Digital Photography' started by Ubiquitous, Dec 23, 2003.

  1. Ubiquitous

    Ubiquitous Guest

    "Comancheros >" <<> wrote in message
    news:...
    > 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.
     
    Ubiquitous, Dec 23, 2003
    #1
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  2. Ubiquitous

    Jim Townsend Guest

    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 Townsend, Dec 23, 2003
    #2
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  3. Ubiquitous

    Comancheros Guest

    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
     
    Comancheros, Dec 23, 2003
    #3
  4. Ubiquitous

    Christian Guest

    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.,
    1024x768). 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.
     
    Christian, Dec 23, 2003
    #4
  5. Ubiquitous

    BF Guest

    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" <> wrote in message
    news:bs8dl6$6iq$...
    > 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.,
    > 1024x768). 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.
     
    BF, Dec 23, 2003
    #5
  6. Ubiquitous

    hydra Guest

    On Mon, 22 Dec 2003 20:05:27 -0600, Jim Townsend <>
    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
     
    hydra, Dec 23, 2003
    #6
  7. Ubiquitous

    hydra Guest

    On Mon, 22 Dec 2003 20:05:27 -0600, Jim Townsend <>
    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.
     
    hydra, Dec 23, 2003
    #7
  8. Ubiquitous

    hydra Guest

    On Mon, 22 Dec 2003 20:05:27 -0600, Jim Townsend <>
    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.
     
    hydra, Dec 23, 2003
    #8
  9. Ubiquitous

    Jim Townsend Guest

    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
     
    Jim Townsend, Dec 24, 2003
    #9
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