Nathan ...
What you say I understand fully, but what I think is missing is the fact
that a print is a piece of paper covered in ink and that, other things being
equal, more ink within reason will make a better print.
The printer is driven by a digital image whose length and breadth is
measured in pixels. The print size is largely or wholly dictated by the
image's pixel resolution. As the pixels per inch increase the physical size
of the final print deacreases and vice versa.
Thus, an image with few pixels per inch being printed by a printer capable
of only a few dots per inch of ink delivery will result in a poor quality
print.
As the image's pixel resolution increases [more concentration of colour /
tone / contrast, etc information] coupled with a printer that can deliver
more dots per inch of ink must result in a better print because [1] there is
more image information for every inch of digital image, and [2] more ink per
inch is being put on the paper.
Thus, in my mind the key issue is optimizing the combination of [1] the
image's pixels per inch resolution and [2] the rate per inch at which the
printer can deliver dots of ink to the paper. If [1] and [2] are optimized
one gets an ideal print or so I think. If there is an imbalance between [1]
and [2] there is either too much image information [too many pixels per
inch] for the printer to cope with or not enough image information leaving
the printer to underperform.
Is there a formula or rule of thumb for optimizing the combination of pixel
resolution and the dot rate per inch at which the ink is put on the photo
paper.
John Hudson
ps: Both of these pieces are interesting reading
http://desktoppub.about.com/cs/intermediate/a/measure_dpi.htm
http://en.wikipedia.org/wiki/Dots_per_inch
----- Original Message -----
From: "Nathan Wajsman" <>
To: "Olympus Camera Discussion" <>
Sent: Tuesday, January 13, 2009 12:04 PM
Subject: Re: [OM] dots and pixels per inch
> John,
>
> This is one of the most misunderstood aspects of digital photography,
> and the amount of confusion out there is actually very simple. An
> image, whether scanned or captured digitally, has a size, measured in
> pixels. For example, 4000x3000 pixels (from a 12 MP camera, to use
> round numbers). You can print such an image in various sizes, each of
> which will have a different resolution. For example, if you print it
> as 10x8 inches, the resultion will be 400 pixels per inch (measured on
> the long side).
>
> When your photo lab asks for images with at least 300 pixels per inch,
> what they mean is that you should provide an image of sufficient pixel
> dimensions to yield a resolution of 300 ppi. In the above example, if
> you ask them to make a 10x8 inch print or smaller, you are fine. If
> you ask them to make a print that is 2 feet on the long side, then
> your resolution will be only 4000/24=167 ppi, and the print will not
> have sufficient definition according to their standards.
>
> So, in a nutshell, it is misleading of an image having a resolution of
> x. It has pixel dimensions of x by z, and the resolution dependes
> entirely on the size of the print you wish to make from it.
>
> Nathan
>
> Nathan Wajsman
> Alicante, Spain
> http://www.frozenlight.eu
> http://www.greatpix.eu
> http://www.nathanfoto.com
>
> Books: http://www.blurb.com/bookstore/search?search=wajsman&x=0&y=0
> PICTURE OF THE WEEK: http://www.fotocycle.dk/paws
> Blog: http://www.fotocycle.dk/blog
>
>
>
> On Jan 13, 2009, at 3:56 PM, John Hudson wrote:
>
>> To quote www.NetLingo.com
>>
>> "Resolution
>> "A common computing term, it refers to several things. On a computer
>> monitor, it is the number of pixels (horizontally) and lines
>> (vertically) on
>> the screen. For printers, resolution is a measurement expressed in
>> dpi that
>> describes the sharpness of a printed image. With sound boards, it is
>> the
>> number of bits used to encode sounds. And in business, it describes
>> some
>> form of mutual agreement."
>>
>>
>>
>> My printer will work at the following print resolutions; draft,
>> 360d[ots]
>> per inch through various steps to 2880 d[ots] per inch
>>
>> Whenever I get prints done out of the house the photo lab asks for
>> images at
>> no less than 300 p[ixels] per inch.
>>
>> Is anyone able to provide a clear explanation of the relationship
>> between
>> pixels per inch and dots per inch ?
>>
>> Does an increase in pixels per inch generate an increase in dots per
>> inch or
>> are the two mutally exclusive ?
>>
>> If a printer's technology can only deliver a maximum or so many dots
>> per
>> inch is there a formula to show that an image resolution beyond so
>> many
>> pixels an inch is un-necessary ?
>>
>> If this question has already been flogged to death I apologise for
>> asking
>> again.
>>
>> John Hudson
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>> --
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