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Dots and Pixels

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Anonymous
March 14, 2005 3:01:07 AM

Archived from groups: comp.periphs.printers (More info?)

Anyone (who uses Photoshop) and has a good understanding of the
difference between pixels and dots per inch. I know that printers print
in dots per inch and monitors display in pixels per inch.

If you have a photo that has a resolution of 400 pixels per inch (using
1024x768) how can you tell the dots per inch that the printer will print at?

How can you tell and equate the levels of quality to dots per inch. My
printer can print a resolution of over 1200 dots per inch. Taking my
400 pixel photo, what will it really print out at and how do you
calculate it..

More about : dots pixels

Anonymous
March 14, 2005 4:25:29 AM

Archived from groups: comp.periphs.printers (More info?)

In article <7v4Zd.9934$C47.9877@newssvr14.news.prodigy.com>, measekite
<measekite@yahoo.com> writes
>Anyone (who uses Photoshop) and has a good understanding of the
>difference between pixels and dots per inch. I know that printers
>print in dots per inch and monitors display in pixels per inch.
>
And images are made from pixels.

>If you have a photo that has a resolution of 400 pixels per inch (using
>1024x768) how can you tell the dots per inch that the printer will
>print at?
>
It will print at whatever dots per inch you tell it to print at - it has
nothing at all to do with the pixels.

>How can you tell and equate the levels of quality to dots per inch.

The more dots per inch the better. The printer can only print a dot of
ink or not, and it only has ink in a few colours. So, when it tries to
reproduce a particular colour of, say, a pixel in an image it does this
by varying the number of dots it prints of each of the colours that it
has. This process is called dithering. Some inkjet printers might only
have 4 colours: cyan, magenta, yellow and black, others have more, such
as light cyan and light magenta. Printers with more ink colours require
less dithering, which means that they can either produce finer colour
variations or they require less dots per inch to achieve the same colour
variation.

To make this even more complicated, the dither pattern does not need to
occur entirely within an individual pixel. In other words, it doesn't
matter if the colour of each pixel is accurate - as long as the average
colour is. So the printer uses a complicated algorithm to print each
pixel on the image, measuring the actual colour that it creates from the
dots it prints and then calculating the difference between that and the
colour that the pixel should be. This colour error is then shared
between the adjacent pixels that have not been printed yet, so that they
compensate for the error. The process of error compensation continues
to the edge of the page.

The advantage of this is that for large areas with a specific colour or
a gradually changing colour, the actual colour is determined by the dots
of ink that are placed across the entire area, not just in the
individual pixel. So the colour can be controlled very precisely.
However, when there is a sudden change of colour between pixels, such as
on an edge, the same algorithm can reproduce that edge with pixel
accuracy.

Using some of these advance algorithms you can readily print an image
with a few colours of ink where only one or two dots of ink are placed
per pixel and still get both the fine colour tonality and the pixel
resolution in your image.

> My printer can print a resolution of over 1200 dots per inch. Taking
>my 400 pixel photo, what will it really print out at and how do you
>calculate it..
>
You don't - the printer driver does it all for you, completely
transparently. You just tell it what dpi you want it to place the ink
dots at, based on the printer's capabilities, and the printer driver
decides where the dots should be placed, how often and what colours. The
dpi you choose is determined by the media you are using and the quality
of the print you want - not the ppi of the image. With high quality
paper you should always use the highest dot resolution that the printer
offers. With poorer paper, the ink bleeds into the paper and spreads so
there is little advantage to using the finest dot resolution of the
printer and a lower resolution is likely to print faster - but it
probably won't save any ink, unless you printer offers a draft mode,
where the image can be lighter than the final version.

So, forget about the printer dpi other than matching it to your paper
stock. What you really need to worry about is your image ppi. To all
intents and purposes, you can't see a significant benefit by printing at
more than 300ppi unless you want to view the image under magnification
(and there are some cases where you might want to do that - such as a
sheet of "contact" prints). However if you get below about 200ppi then
the individual pixels in the image become quite visible, and by 100ppi
are quite objectionable even from a reasonable distance. So your
400pixel image would look as good as a photo booth print if you print it
no more than 1.5inches wide/high, and will progressively become more
visibly pixelated as you increase the size. Of course, if you view it
from a sufficient distance the pixelation will be less visible, but you
will see it close up with sizes of 3inch or more on a decent photo
quality printer. (This, of course, assumes you really mean a 400pixel
wide/high image, and not a 400ppi image as you referred to earlier - a
1024x768 pixel image can easily be printed at 5x3.5inches without too
much visible pixelation.)

Your printer may offer a special mode of printing which reduces the
visibility of the pixels by interpolating between them, but you will
have to enable this in the driver option page. On Epson printers it is
usually called "DCC" or "digital camera correction" or something
similar. If the printer does not have this option then you can upsample
the original image in Photoshop or other software to get sufficient
pixels to make them indiscernable on the page - aim for 200ppi as a
minimum with a photo quality printer. This is exactly the same as the
printer is doing in its special, low resolution image, mode but it is a
little slower because you are sending the printer more data. The upside
is that most software packages offer several upsampling interpolation
algorithms, some of which are likely to be better quality than the
printer's simple version.

A final issue is the printer's native image resolution. This is not the
ink dots per inch, but the pixels per inch that the printer driver uses
when the image is rasterised. For all Epson desktop printers this is
currently 720ppi, but other manufacturers vary - and it is not a number
that they generally publish, you either get it from someone who knows or
work it out using devious test images, like I did! ;-)

The optimum image resolution to sent to the printer should *never*
exceed this native resolution (because the driver will just ignore the
extra pixels and you have no control over how it does that) and should
be an integer division of it, so that each pixel in the image is
resampled to the same number of pixels in the printer driver
rasterisation. So, while the optimum for HP printers is often quoted as
being 300ppi, the optimum for Epson is 360ppi or, the next one down,
240ppi. In practice, the degradation caused by being off optimum is
negligible for most photographic images, but for certain images with a
lot of repetitive fine detail, for example, a picket fence or bricks in
a wall, it can be quite noticeable.

Hope that helps.
--
Kennedy
Yes, Socrates himself is particularly missed;
A lovely little thinker, but a bugger when he's pissed.
Python Philosophers (replace 'nospam' with 'kennedym' when replying)
March 14, 2005 5:56:26 AM

Archived from groups: comp.periphs.printers (More info?)

"measekite" <measekite@yahoo.com> wrote in message
news:7v4Zd.9934$C47.9877@newssvr14.news.prodigy.com...
> Anyone (who uses Photoshop) and has a good understanding of the
> difference between pixels and dots per inch. I know that printers print
> in dots per inch and monitors display in pixels per inch.
>
> If you have a photo that has a resolution of 400 pixels per inch (using
> 1024x768) how can you tell the dots per inch that the printer will print
at?
>
You tell the printer the number of dots per inch. A good starting place is
3 dots per pixel, but you might find that you like more than that.
FYI, 400 pixels per inch is an overkill. I can't see any difference between
300 and anything higher.
> How can you tell and equate the levels of quality to dots per inch. My
> printer can print a resolution of over 1200 dots per inch. Taking my
> 400 pixel photo, what will it really print out at and how do you
> calculate it..
This is controlled by the printer driver software. You set the number.
Jim
>
Related resources
Anonymous
March 14, 2005 6:42:05 AM

Archived from groups: comp.periphs.printers (More info?)

No printer prints better than the digital equivalent of 360 dpi. Many people
think even this degree of resolution is a fantasy of printer manufacturers
and there is no clear way to objectively verify the spec. No consumer
publication has ever conducted a clear objective study of this issue because
it is impossible to do so. Paper surfaces, local humidity and other factors
impact on this specification anyway.

In practice photographers claim that they get high quality prints at
settings ranging from 200dpi to that theoretical maximum of 360 dpi. Subject
matter in the print, as well as the size of the print, are important issues
in concealing banding, dithering and other artifacts that may really reside
in the print or only in the imagination of the viewer. These newsgroups are
filled by imaginative people.

As a practical matter, in Photoshop you can specify a dpi, in which case
there is never a point in setting a printer dpi greater than 360 dpi, or let
the printer driver do it for you. If the dpi you specify in the image size
function of Photoshop exceeds what the printer can produce, or the image can
be scaled to, the printer driver will arbitrarily scale the image to
whatever it is able to produce anyway. The driver gives you no information
on this subject and you can exercise no control over the process.

Somewhat but related off-topic (because it deals with the immutable
algorithms that control printer drivers): if you have the fantasy that
working in 16 bit color gives you more complete control over the final
printed image than working in 8 bit color I urge you to research this issue.
What happens when 16 bit color is outside the gamut of 8 bit color? Do you
think your printer can reproduce the entire 8 bit color gamut anyway?
Anonymous
March 14, 2005 1:46:01 PM

Archived from groups: comp.periphs.printers (More info?)

measekite wrote:
> Anyone (who uses Photoshop) and has a good understanding of the
> difference between pixels and dots per inch. I know that printers print
> in dots per inch and monitors display in pixels per inch.
>
> If you have a photo that has a resolution of 400 pixels per inch (using
> 1024x768) how can you tell the dots per inch that the printer will print
> at?

Do not confuse the pixels/inch of the monitor and the pixels/inch of the
image. They are different things. Check the EXIF data to see pixels per
inch of the image itself. For example, a nominallly 4"x6" photograph at
400 pixels/inch will be 1600x2400 on the monitor, not 768x1024. But a
400 pixel/inch image of 1024x768 size is only about 2-1/2"x2".

Suppose, 1200 dpi is the maximum dpi the printer is capable of; it will
print at this pitch when set for highest quality printing. At lower
qualities, it will print at lower dpi; this is why draft mode saves ink.
However, the printing software will adjust the image information for the
size and quality of the printed image. Hence pixels/inch and dpi have no
obvious relation to each other. See below.

> How can you tell and equate the levels of quality to dots per inch. My
> printer can print a resolution of over 1200 dots per inch. Taking my
> 400 pixel photo, what will it really print out at and how do you
> calculate it.

The printer resolution of 1200 dpi is equal to 300 dpi for each colour,
so the resolution in pixels is about 300 pixels/inch, more or less. The
actual pixel resolution depends on how the ink dots are clustered, which
may be a reason that printer manufacturers don't specify pixels. A more
likely reaon is that dpi gives you bigger numbers, and bigger is better,
right? :-) Anyhow, it means that means a 1200x800 pixel image will print
out at at about 4"x2.3" when printed to "fit resolution."

But it's not that simple. You have to understand pixels, resolution, dot
pitch, dots per inch, and their relationship. I hope my explanation
below is clear enough (and correct - if anyone finds errors, kindly set
them right.)

If your printer panel lets you to select modes, print the same image in
fit-pixels, fit-resolution, and fit-to-page mode. By fiddling with the
margins, you can print all three on the same page, in three passes
through the printer. Set the fit-to-page so the image is about 6-7" wide.
Print a series of images of different sizes, ie, 480x320. 640x480,
800x600, 1200x800, etc. (These must be image size, _not_ monitor
resolutions.) This will show you how image size and mode relate to each
other, and how both affect quality. It's an eye-opener. Most
importantly, it will show you that the smaller the original image, the
more pronounced the "jaggies" when you print it large.

Be careful not to confuse the smoothed out image on the screen with
what's actually sent to the printer. If you have set the software to
display an image "fit to window", or "fit to screen", it will display a
smoothed out image, but this smoothed out image will _not_ be sent to
the printer. The printer will get the original image, and the printing
software will enlarge or reduce that image to fit the specified size on
the page. Hence the jaggies. (This is why it's a bad idea to set a
digital camera to low resolution. You get more pictures on the card, but
they will be small.) To smoothe out the jaggies, you must resize the
image (which may blur it somewhat, too.)

Pixels, dot pitch, and dots per inch. This information may help you
understand why dpi, pixels, and print quality have such a complicated
relationship. But you can skip it. If so, go directly to Bottom Line. :-)
A "pixel" on screen is a cluster of three colured dots. The monitor
lights up each one differently, which produces the different colours. A
monitor is specified in:
a) maximum "resolution", which tells you the number of pixels
horizontally and vertically. Generally, you should run the monitor at
maxiumum resolution for the sharpest displayed images.
b) "dot pitch" which tells you the size of the dots (as a fraction of a
mm, eg 0.26mm, 0.28mm, etc.) Two different sized monitors with the same
dot pitch will have different maximum resolutions. But electronics also
plays a role in maximum resolution, so a larger monitor will often have
a larger dot pitch than a small monitor. At normal viewing distance, the
larger monitor will look less sharp.

A printer is specified in "dots per inch". But in order to get different
colours, a cluster of different coloured dots must be laid down. Thus, a
printer actually prints pixels, too. But -- there's a couple of catches:
1) On different papers, the ink soaks in and spreads differently.
2) Pigment and dye inks mix differently to produce any given colour.
3) When you print at different qualities, there will be more or less of
the paper's own colour showing through, which affects the colour, too.
Eg, in draft mode, there will be lots of white space between the dots.
4) The chemistry of the paper (pH, mostly, but that's not the only
factor) may change the colour of the inks.
So, the printer must control
a) the placement of the ink drops; and
b) the amount of ink actually deposited.
It must do so for different types of paper, different modes, and
different qualities of printing. Hence so-called "colour profiles",
among other things. Each manufacturer tries to match inka and paper
chemistry, too, which is why their own branded papers often give the
better results than 3rd party papers.

Bottom Line:
To get the sharpest large prints, you must use the largest images
(2048x1768 is minimum IMO), and use the correct quality + paper
combination. A 2048 by 1768 image printed at fit-resolution on a
1200dpi (=300 pixel/inch) printer will be about 7"x6".

HTH&GL
Anonymous
March 14, 2005 4:19:55 PM

Archived from groups: comp.periphs.printers (More info?)

In article <hK7Zd.21473$OU1.12732@newssvr21.news.prodigy.com>, bmoag
<apquilts@pacbell.net> writes
>No printer prints better than the digital equivalent of 360 dpi.

I disagree with that and have the evidence to disprove it.

> Many people
>think even this degree of resolution is a fantasy of printer manufacturers
>and there is no clear way to objectively verify the spec.

There certainly is! I have a print here in front of me, made several
years ago, which has various test patterns printed on it at a range of
resolutions and 720ppi is clearly distinguished in all colours and
densities under x10 magnification. There is certainly more bleed than
at lower resolutions, but there is no question that 720ppi is resolved.
And before anyone suggests that test patterns are not real images, they
are images designed to measure the capabilities of equipment in a
quantifiable form.
--
Kennedy
Yes, Socrates himself is particularly missed;
A lovely little thinker, but a bugger when he's pissed.
Python Philosophers (replace 'nospam' with 'kennedym' when replying)
Anonymous
March 14, 2005 6:54:48 PM

Archived from groups: comp.periphs.printers (More info?)

Jim wrote:

>"measekite" <measekite@yahoo.com> wrote in message
>news:7v4Zd.9934$C47.9877@newssvr14.news.prodigy.com...
>
>
>>Anyone (who uses Photoshop) and has a good understanding of the
>>difference between pixels and dots per inch. I know that printers print
>>in dots per inch and monitors display in pixels per inch.
>>
>>If you have a photo that has a resolution of 400 pixels per inch (using
>>1024x768) how can you tell the dots per inch that the printer will print
>>
>>
>at?
>
>
>You tell the printer the number of dots per inch. A good starting place is
>3 dots per pixel, but you might find that you like more than that.
>FYI, 400 pixels per inch is an overkill. I can't see any difference between
>300 and anything higher.
>
>
Are you saying that in Photoshop after you crop and look at the image
size dialog box; if the total resolution is over 300 PIXELS per inch -
that is all you need? You mean that there is no need to increase the
Pixels in Photoshop? Does the Canon automatically print at is full
capability of 1200 dots per inch? At 300 Pixels times 3 is the printer
printing at 900 dots per inch in this case? A little confused!

>>How can you tell and equate the levels of quality to dots per inch. My
>>printer can print a resolution of over 1200 dots per inch. Taking my
>>400 pixel photo, what will it really print out at and how do you
>>calculate it..
>>
>>
>This is controlled by the printer driver software. You set the number.
>Jim
>
>
>
>
>
How?
Anonymous
March 14, 2005 6:59:24 PM

Archived from groups: comp.periphs.printers (More info?)

bmoag wrote:

>No printer prints better than the digital equivalent of 360 dpi.
>

In PIXELS, what is the pixel equivalent of 360 dots per inch? And why
does my Canon printer claim to print at 1200 dpi? Do they take RGB and
claim 1200 that reduces to 300 dpi for each color?

>Many people
>think even this degree of resolution is a fantasy of printer manufacturers
>and there is no clear way to objectively verify the spec. No consumer
>publication has ever conducted a clear objective study of this issue because
>it is impossible to do so. Paper surfaces, local humidity and other factors
>impact on this specification anyway.
>
>In practice photographers claim that they get high quality prints at
>settings ranging from 200dpi to that theoretical maximum of 360 dpi.
>
Photoshop resolution does not measure in DPI but PPI(pixels per inch)
What is the formular to convert any DPI to PPI or PPI to DPI?


>Subject
>matter in the print, as well as the size of the print, are important issues
>in concealing banding, dithering and other artifacts that may really reside
>in the print or only in the imagination of the viewer. These newsgroups are
>filled by imaginative people.
>
>As a practical matter, in Photoshop you can specify a dpi, in which case
>there is never a point in setting a printer dpi greater than 360 dpi, or let
>the printer driver do it for you. If the dpi you specify in the image size
>function of Photoshop exceeds what the printer can produce, or the image can
>be scaled to, the printer driver will arbitrarily scale the image to
>whatever it is able to produce anyway. The driver gives you no information
>on this subject and you can exercise no control over the process.
>
>Somewhat but related off-topic (because it deals with the immutable
>algorithms that control printer drivers): if you have the fantasy that
>working in 16 bit color gives you more complete control over the final
>printed image than working in 8 bit color I urge you to research this issue.
>What happens when 16 bit color is outside the gamut of 8 bit color? Do you
>think your printer can reproduce the entire 8 bit color gamut anyway?
>
>
>
>
Anonymous
March 14, 2005 7:07:05 PM

Archived from groups: comp.periphs.printers (More info?)

bmoag wrote:

>No printer prints better than the digital equivalent of 360 dpi. Many people
>think even this degree of resolution is a fantasy of printer manufacturers
>and there is no clear way to objectively verify the spec. No consumer
>publication has ever conducted a clear objective study of this issue because
>it is impossible to do so. Paper surfaces, local humidity and other factors
>impact on this specification anyway.
>
>In practice photographers claim that they get high quality prints at
>settings ranging from 200dpi to that theoretical maximum of 360 dpi. Subject
>matter in the print, as well as the size of the print, are important issues
>in concealing banding, dithering and other artifacts that may really reside
>in the print or only in the imagination of the viewer. These newsgroups are
>filled by imaginative people.
>
>
>
What your brain sees (not your eyes) is really there regardless of
whether it is there?

>As a practical matter, in Photoshop you can specify a dpi, in which case
>there is never a point in setting a printer dpi greater than 360 dpi, or let
>the printer driver do it for you. If the dpi you specify in the image size
>function of Photoshop exceeds what the printer can produce, or the image can
>be scaled to, the printer driver will arbitrarily scale the image to
>whatever it is able to produce anyway. The driver gives you no information
>on this subject and you can exercise no control over the process.
>
>
>
I findwith the Canon IP4000 that if the Pixels (wide) and the Pixels
(long) exceed what the printer can produce, part of the image will not
be there. In other word if the print is 4" wide and the printer is at
1200 DPI than you will get 4800 across. If the photo is 6000 across,
1200 pixels of the photo will not be there.


>Somewhat but related off-topic (because it deals with the immutable
>algorithms that control printer drivers): if you have the fantasy that
>working in 16 bit color gives you more complete control over the final
>printed image than working in 8 bit color I urge you to research this issue.
>What happens when 16 bit color is outside the gamut of 8 bit color? Do you
>think your printer can reproduce the entire 8 bit color gamut anyway?
>
>
>
>
Anonymous
March 14, 2005 7:43:19 PM

Archived from groups: comp.periphs.printers (More info?)

Kennedy McEwen wrote:

> In article <hK7Zd.21473$OU1.12732@newssvr21.news.prodigy.com>, bmoag
> <apquilts@pacbell.net> writes
>
>> No printer prints better than the digital equivalent of 360 dpi.
>
>
> I disagree with that and have the evidence to disprove it.


Please explain. I would like to understand this and would like to know
how to set up Photoshop and the Printer to achieve the best.

>
>> Many people
>> think even this degree of resolution is a fantasy of printer
>> manufacturers
>> and there is no clear way to objectively verify the spec.
>
>
> There certainly is! I have a print here in front of me, made several
> years ago, which has various test patterns printed on it at a range of
> resolutions and 720ppi is clearly distinguished in all colours and
> densities under x10 magnification. There is certainly more bleed than
> at lower resolutions, but there is no question that 720ppi is resolved.
> And before anyone suggests that test patterns are not real images,
> they are images designed to measure the capabilities of equipment in a
> quantifiable form.
Anonymous
March 15, 2005 3:07:13 AM

Archived from groups: comp.periphs.printers (More info?)

In article <HajZd.21634$OU1.9261@newssvr21.news.prodigy.com>, measekite
<measekite@yahoo.com> writes
>
>
>Kennedy McEwen wrote:
>
>> In article <hK7Zd.21473$OU1.12732@newssvr21.news.prodigy.com>, bmoag
>><apquilts@pacbell.net> writes
>>
>>> No printer prints better than the digital equivalent of 360 dpi.
>>
>>
>> I disagree with that and have the evidence to disprove it.
>
>
>Please explain. I would like to understand this and would like to know
>how to set up Photoshop and the Printer to achieve the best.
>
I think that the loose terminology used by bmoag, which I had ignored
because the context implied it was in error, has confused you somewhat.
Bmoag is actually claiming that the printer cannot achieve better than
360ppi - every inkjet printer on the market today does better than
360dpi.

I was disputing the suggestion that 360ppi is a resolution limit - I
have images which clearly demonstrate much higher resolution test
patterns, even at relatively low contrast, and regularly print sheets of
"contacts" at the full 720ppi of my Epson - and more information is
certainly there than on a 360ppi print, although I do need a lupe to see
it.
--
Kennedy
Yes, Socrates himself is particularly missed;
A lovely little thinker, but a bugger when he's pissed.
Python Philosophers (replace 'nospam' with 'kennedym' when replying)
Anonymous
March 15, 2005 4:25:07 PM

Archived from groups: comp.periphs.printers (More info?)

You are mixing up two different related but not equivalent concepts.

The dots referred to regarding your printer are addressable dot
locations. They do not equal a pixel. As you likely know, a pixel can
be any of 16.8 million colors with a 24 bit display (8 bits per color
RGB). However, even if your printer was capable of reproducing 16.8
million colors (it's not, it has a much more limited gamut) there is no
way any one dot could be any one of those shades of colors.

Instead, printers use a number of colors and placement of dots to
represent a pixel or a specific color. Usually, a cluster of colored
dots from different colored inks, plus some background white coming
through makes up the illusion of a pixel color.

Therefore, as far as PPI (pixels per inch), and the often misused dpi
(dots per inch) they are an equal number, in the seen that when you
print from Photoshop, at 400 ppi, the printed result is indeed 400 "dpi"
or ppi output, at the same size from the source file.

Most drug store prints are at about 200 ppi, while custom photos are up
to 300 ppi.

I am not further confounding this with actual pip versus interpolated or
upsampled ppi.

Further still, inkjet printer spoolers actually usually spool to one or
two resolutions only, so the Photoshop resolution, nor likely the
selected printer resolution is the resolution the printer creates the
spooled file in.

Art

measekite wrote:

> Anyone (who uses Photoshop) and has a good understanding of the
> difference between pixels and dots per inch. I know that printers print
> in dots per inch and monitors display in pixels per inch.
>
> If you have a photo that has a resolution of 400 pixels per inch (using
> 1024x768) how can you tell the dots per inch that the printer will print
> at?
>
> How can you tell and equate the levels of quality to dots per inch. My
> printer can print a resolution of over 1200 dots per inch. Taking my
> 400 pixel photo, what will it really print out at and how do you
> calculate it..
>
Anonymous
March 15, 2005 4:36:09 PM

Archived from groups: comp.periphs.printers (More info?)

I just noted that Kennedy responded to your post in a great deal more
detail than I did. His explanation provides you with a more complete
answer to your question.

Art

Arthur Entlich wrote:

> You are mixing up two different related but not equivalent concepts.
>
> The dots referred to regarding your printer are addressable dot
> locations. They do not equal a pixel. As you likely know, a pixel can
> be any of 16.8 million colors with a 24 bit display (8 bits per color
> RGB). However, even if your printer was capable of reproducing 16.8
> million colors (it's not, it has a much more limited gamut) there is no
> way any one dot could be any one of those shades of colors.
>
> Instead, printers use a number of colors and placement of dots to
> represent a pixel or a specific color. Usually, a cluster of colored
> dots from different colored inks, plus some background white coming
> through makes up the illusion of a pixel color.
>
> Therefore, as far as PPI (pixels per inch), and the often misused dpi
> (dots per inch) they are an equal number, in the seen that when you
> print from Photoshop, at 400 ppi, the printed result is indeed 400 "dpi"
> or ppi output, at the same size from the source file.
>
> Most drug store prints are at about 200 ppi, while custom photos are up
> to 300 ppi.
>
> I am not further confounding this with actual pip versus interpolated or
> upsampled ppi.
>
> Further still, inkjet printer spoolers actually usually spool to one or
> two resolutions only, so the Photoshop resolution, nor likely the
> selected printer resolution is the resolution the printer creates the
> spooled file in.
>
> Art
>
> measekite wrote:
>
>> Anyone (who uses Photoshop) and has a good understanding of the
>> difference between pixels and dots per inch. I know that printers
>> print in dots per inch and monitors display in pixels per inch.
>>
>> If you have a photo that has a resolution of 400 pixels per inch
>> (using 1024x768) how can you tell the dots per inch that the printer
>> will print at?
>>
>> How can you tell and equate the levels of quality to dots per inch.
>> My printer can print a resolution of over 1200 dots per inch. Taking
>> my 400 pixel photo, what will it really print out at and how do you
>> calculate it..
>>
Anonymous
March 16, 2005 2:07:58 AM

Archived from groups: comp.periphs.printers (More info?)

On Tue, 15 Mar 2005 00:07:13 +0000, Kennedy McEwen
<rkm@nospam.demon.co.uk> wrote:

>In article <HajZd.21634$OU1.9261@newssvr21.news.prodigy.com>, measekite
><measekite@yahoo.com> writes
>>
>>
>>Kennedy McEwen wrote:
>>
>>> In article <hK7Zd.21473$OU1.12732@newssvr21.news.prodigy.com>, bmoag
>>><apquilts@pacbell.net> writes
>>>
>>>> No printer prints better than the digital equivalent of 360 dpi.
>>>
>>>
>>> I disagree with that and have the evidence to disprove it.
>>
>>
>>Please explain. I would like to understand this and would like to know
>>how to set up Photoshop and the Printer to achieve the best.
>>
>I think that the loose terminology used by bmoag, which I had ignored
>because the context implied it was in error, has confused you somewhat.
>Bmoag is actually claiming that the printer cannot achieve better than
>360ppi - every inkjet printer on the market today does better than
>360dpi.
>
>I was disputing the suggestion that 360ppi is a resolution limit - I
>have images which clearly demonstrate much higher resolution test
>patterns, even at relatively low contrast, and regularly print sheets of
>"contacts" at the full 720ppi of my Epson - and more information is
>certainly there than on a 360ppi print, although I do need a lupe to see
>it.

I have seen the same, and again at 1440dpi, though I can't see any
difference at all at 2880dpi.

--

Hecate - The Real One
Hecate@newsguy.com
veni, vidi, reliqui
Anonymous
March 16, 2005 5:01:13 AM

Archived from groups: comp.periphs.printers (More info?)

In article <4lqe31l29803qe2km4r8gr8v7jbi9fmd1o@4ax.com>, Hecate
<hecate@newsguy.com> writes
>
>I have seen the same, and again at 1440dpi, though I can't see any
>difference at all at 2880dpi.
>
Just to be clear on this Hecate, I am talking about printing an image at
720ppi, not selecting 720dpi on the print driver.

Obviously you need at least, and preferably more, than 720dpi to print a
720ppi image.

However the Epson printers will not produce more resolution than 720ppi
because the driver resamples everything to 720ppi before half-toning the
image. So if you send it a 1440ppi test image with 720cy/in patterns,
it just prints solid colour with no detail. Anything above 720ppi is
just aliased by the crude downsampling algorithm of the print driver.

It is a combination of this driver native resolution and the maximum
pixel sizes supported by Photoshop and similar programs that results in
the 44" print length limit. 32000 pixels at 720ppi is 44.4".

With the wide format professional printers, such as the 7600 and 9600,
the resolution is restricted to 360ppi, so that they can produce twice
as large images with the same restrictions.
--
Kennedy
Yes, Socrates himself is particularly missed;
A lovely little thinker, but a bugger when he's pissed.
Python Philosophers (replace 'nospam' with 'kennedym' when replying)
Anonymous
March 17, 2005 2:21:52 AM

Archived from groups: comp.periphs.printers (More info?)

On Wed, 16 Mar 2005 02:01:13 +0000, Kennedy McEwen
<rkm@nospam.demon.co.uk> wrote:

>In article <4lqe31l29803qe2km4r8gr8v7jbi9fmd1o@4ax.com>, Hecate
><hecate@newsguy.com> writes
>>
>>I have seen the same, and again at 1440dpi, though I can't see any
>>difference at all at 2880dpi.
>>
>Just to be clear on this Hecate, I am talking about printing an image at
>720ppi, not selecting 720dpi on the print driver.
>
>Obviously you need at least, and preferably more, than 720dpi to print a
>720ppi image.

Ah, it's the old ppi/dpi thing. Yes, I assumed when you said dpi you
were referring to print. Me, a pedant? ;-)

>However the Epson printers will not produce more resolution than 720ppi
>because the driver resamples everything to 720ppi before half-toning the
>image. So if you send it a 1440ppi test image with 720cy/in patterns,
>it just prints solid colour with no detail. Anything above 720ppi is
>just aliased by the crude downsampling algorithm of the print driver.

Interesting. It must be a case of perception then as it has always
seemed to me that the 1440 dpi setting has produced better prints.
I'm, quite happy to accept what you say though as I know you've done a
lot of research in this area and you undoubtedly know more about it
than I do.

>It is a combination of this driver native resolution and the maximum
>pixel sizes supported by Photoshop and similar programs that results in
>the 44" print length limit. 32000 pixels at 720ppi is 44.4".

Useful info.

>With the wide format professional printers, such as the 7600 and 9600,
>the resolution is restricted to 360ppi, so that they can produce twice
>as large images with the same restrictions.

Didn't know that and I was looking at a larger printer so I'll
remember that.

--

Hecate - The Real One
Hecate@newsguy.com
Fashion: Buying things you don't need, with money
you don't have, to impress people you don't like...
Anonymous
March 17, 2005 4:46:54 AM

Archived from groups: comp.periphs.printers (More info?)

In article <pmfh31d0vft04ghj03rf5026qb65o5li1p@4ax.com>, Hecate
<hecate@newsguy.com> writes
>On Wed, 16 Mar 2005 02:01:13 +0000, Kennedy McEwen
><rkm@nospam.demon.co.uk> wrote:
>>Just to be clear on this Hecate, I am talking about printing an image at
>>720ppi, not selecting 720dpi on the print driver.
>>
>>Obviously you need at least, and preferably more, than 720dpi to print a
>>720ppi image.
>
>Ah, it's the old ppi/dpi thing. Yes, I assumed when you said dpi you
>were referring to print. Me, a pedant? ;-)
>
That's why I said ppi! ;-)
>
>Interesting. It must be a case of perception then as it has always
>seemed to me that the 1440 dpi setting has produced better prints.

Yes 1440dpi certainly produces better prints, as does 2880dpi, but that
is because the driver is using a finer dither to reproduce each pixel -
you are getting more dots per pixel. But since there are no more than
720 pixels per inch, you are not getting better resolution. There is
more to good prints than resolution. ;-)

>I'm, quite happy to accept what you say though as I know you've done a
>lot of research in this area and you undoubtedly know more about it
>than I do.
>
Its easy enough to prove for yourself. Create a pattern of lines that
are one pixel wide and one pixel apart in each of the ink colours. Then
print this at a few ppi off of the likely optimum - you know its 720ppi
because I told you, but I had to run a lot of tests first. ;-) What
you will see is alias patterns of broad bands. The spatial frequency of
the bands is just the difference between the input (half the ppi that
you are printing at) and the Nyquist of the native resolution
(360cy/in). Some quick measurements and checks at higher and lower
harmonics of this confirm that 720 is the native resolution.
>
>>With the wide format professional printers, such as the 7600 and 9600,
>>the resolution is restricted to 360ppi, so that they can produce twice
>>as large images with the same restrictions.
>
>Didn't know that and I was looking at a larger printer so I'll
>remember that.
>
Yes - its a pity they don't use a dynamic driver that only selects the
lower native resolution if the print size justifies it. But it really
only makes a difference if you are printing things that you will look at
under magnification - and I doubt that many large format printers are
put to that task.
--
Kennedy
Yes, Socrates himself is particularly missed;
A lovely little thinker, but a bugger when he's pissed.
Python Philosophers (replace 'nospam' with 'kennedym' when replying)
Anonymous
March 18, 2005 1:43:11 AM

Archived from groups: comp.periphs.printers (More info?)

On Thu, 17 Mar 2005 01:46:54 +0000, Kennedy McEwen
<rkm@nospam.demon.co.uk> wrote:


>>Interesting. It must be a case of perception then as it has always
>>seemed to me that the 1440 dpi setting has produced better prints.
>
>Yes 1440dpi certainly produces better prints, as does 2880dpi, but that
>is because the driver is using a finer dither to reproduce each pixel -
>you are getting more dots per pixel. But since there are no more than
>720 pixels per inch, you are not getting better resolution. There is
>more to good prints than resolution. ;-)

Of course. There's also times when I don't think things through
clearly and it appears this is one of them :) 

>>I'm, quite happy to accept what you say though as I know you've done a
>>lot of research in this area and you undoubtedly know more about it
>>than I do.
>>
>Its easy enough to prove for yourself. Create a pattern of lines that
>are one pixel wide and one pixel apart in each of the ink colours. Then
>print this at a few ppi off of the likely optimum - you know its 720ppi
>because I told you, but I had to run a lot of tests first. ;-) What
>you will see is alias patterns of broad bands. The spatial frequency of
>the bands is just the difference between the input (half the ppi that
>you are printing at) and the Nyquist of the native resolution
>(360cy/in). Some quick measurements and checks at higher and lower
>harmonics of this confirm that 720 is the native resolution.

I'll try that at the weekend - if nothing else it'll be educational :) 

>>>With the wide format professional printers, such as the 7600 and 9600,
>>>the resolution is restricted to 360ppi, so that they can produce twice
>>>as large images with the same restrictions.
>>
>>Didn't know that and I was looking at a larger printer so I'll
>>remember that.
>>
>Yes - its a pity they don't use a dynamic driver that only selects the
>lower native resolution if the print size justifies it. But it really
>only makes a difference if you are printing things that you will look at
>under magnification - and I doubt that many large format printers are
>put to that task.

Yes, right. I was looking at a larger printer of course, so that I
could, well, print larger <g> And at larger sizes you're printing
using lower dpi anyway, generally. :) 

--

Hecate - The Real One
Hecate@newsguy.com
Fashion: Buying things you don't need, with money
you don't have, to impress people you don't like...
!