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High resolution printers - marketing con?

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Anonymous
May 11, 2005 5:04:43 PM

Archived from groups: rec.photo.digital (More info?)

I have been wondering whether the higher and higher print resolutions
claimed by photo printer manufacturers are something of a con.

My latest printer claims a resolution of 9600x2400 dpi. As a software
developer, the first thing I tried to do was to drive the printer mysef,
directly from my own code. I was therefore a little surprised when the
device driver reported back a resolution of only 600dpi in each direction.
In other words, the printer may be capable of up to 9600 different dots in a
single inch but from software I can only specify 600 different colours to
use for those dots. To look at it another way, that line of 9600 coloured
dots actually comprises 600 segments each comprising 16 identically coloured
dots.

So in what sense is that 9600 dpi resolution? Have I missed something here?
Is there a different way of driving the printer other than through the
normal Windows API? If so, it is presumably proprietary so that means I
would only get 9600 dpi using the manufacturer's own software? Pity their
software's user interface is so poor.

It takes a significant amount of time to send a full A4 page worth of pixels
to the printer at 600 dpi. By my calculations, a whole page at 9600x2400
would take 64 times as long, yet the manufacturer's software is, if
anything, faster than mine. All of this leads me to wonder if there are
some porkies being told when these high resolutions are claimed.

I have joined the manufacturer's software developer program but even with
access to the extra documentation that this brings, I still can't see a way
of specifying more than 600 dpi.

Keith
Anonymous
May 11, 2005 5:18:16 PM

Archived from groups: rec.photo.digital (More info?)

"Keith Sheppard" <keith.sheppard@tesco.net> wrote in message
news:Lpnge.2909$V%.2798@newsfe1-gui.ntli.net...
>I have been wondering whether the higher and higher print resolutions
> claimed by photo printer manufacturers are something of a con.
>
> My latest printer claims a resolution of 9600x2400 dpi. As a software
> developer, the first thing I tried to do was to drive the printer mysef,
> directly from my own code. I was therefore a little surprised when the
> device driver reported back a resolution of only 600dpi in each direction.

Your confusing DPI with PPI - the image you send to the printer is 600PPI,
not 600DPI.


> In other words, the printer may be capable of up to 9600 different dots in
> a
> single inch but from software I can only specify 600 different colours to
> use for those dots.

600 colours? Were did that come from?

> To look at it another way, that line of 9600 coloured
> dots actually comprises 600 segments each comprising 16 identically
> coloured
> dots.
> So in what sense is that 9600 dpi resolution?

the 9600DPI is the resolution of the printer's output in DPI.
Anonymous
May 11, 2005 6:10:02 PM

Archived from groups: rec.photo.digital (More info?)

Keith Sheppard wrote:

> I have been wondering whether the higher and higher print resolutions
> claimed by photo printer manufacturers are something of a con.
>
> My latest printer claims a resolution of 9600x2400 dpi. As a software
> developer, the first thing I tried to do was to drive the printer mysef,
> directly from my own code. I was therefore a little surprised when the
> device driver reported back a resolution of only 600dpi in each direction.
> In other words, the printer may be capable of up to 9600 different dots in a
> single inch but from software I can only specify 600 different colours to
> use for those dots. To look at it another way, that line of 9600 coloured
> dots actually comprises 600 segments each comprising 16 identically coloured
> dots.
>
> So in what sense is that 9600 dpi resolution? Have I missed something here?
> Is there a different way of driving the printer other than through the
> normal Windows API? If so, it is presumably proprietary so that means I
> would only get 9600 dpi using the manufacturer's own software? Pity their
> software's user interface is so poor.
>
> It takes a significant amount of time to send a full A4 page worth of pixels
> to the printer at 600 dpi. By my calculations, a whole page at 9600x2400
> would take 64 times as long, yet the manufacturer's software is, if
> anything, faster than mine. All of this leads me to wonder if there are
> some porkies being told when these high resolutions are claimed.
>
> I have joined the manufacturer's software developer program but even with
> access to the extra documentation that this brings, I still can't see a way
> of specifying more than 600 dpi.
>
> Keith

Hi Keith...

I suspect that what's happening here is that you've
stumbled on the single greatest source of confusion
in the business; that of trying to compare dpi and ppi.

Apples and oranges, Keith. Don't even think of them in
the same breath and all will become much clearer.

Let me offer an "introduction to the ppi/dpi" source of
confusion - perhaps it will help the at least the newbies.
At a minimum it will demonstrate why pictures on your
monitor are so much easier than printing them on a
bubblejet. If I'm preaching to the choir, then let me
also apologize in advance.

Like you to look at your monitor with a magnifying glass.
You'll quickly see that each *pixel* is made up of a
triad of one red dot; one blue dot, and one green dot.
For simplicity let's assume that your monitor is an
analogue CRT type.

Now each of those dots - red, blue, and green, can be
set to (virtually) any level of intensity that we choose.

OK, your favorite child or grandchild is wearing an
outfit made up totally of red. (impossible of course,
but allow me, for the moment) Picture on screen will
look good, and if we examine the screen with the glass
almost every red dot will be of differing intensity.

Now let's change the outfit to a purple one. This time
we'll see that almost all the red dots will be different,
and almost all the blue dots will be different. Looks
good, so let's print the purple one with your bubblejet,
and examine the print with a good glass.

Wait a minute... this won't work. On the screen I have
varying intensities of red and blue dots all over the place,
but I forgot to put any purple ink in the printer. Not only
that, but I don't have any differing intensities of purple
ink :) 

So what's going to have to happen is that to print one pixels
worth of purple dress, I'll have to somehow "invent" purple,
right? The printer will do it, but only by dithering intermixed
dots of red and blue. (Please forgive me for simplifying by
giving you an rgb printer rather than cmy)

So, if the outfit is perfect purple one dot of red and one of
blue ad nauseum will give us the illusion of purple. But
each pixel will be shaded differently, so the printer will
mix patterns and repeated dots of same color to come as
close to the original purple pixel as it can. Two red dots,
one blue, repeated will give of course a redder purple, and
so on.

So - I'm an old stroke victim, but if I've explained this
at least well enough for others to understand you'll see
that "dithering" with 9600 dpi will give you far far far
more different colour capabilities than say 2400.

And add to that the fact that each individual dot being smaller
will make for a much smoother picture.

Hope this helps a bit...

Take care.

Ken
Related resources
Anonymous
May 11, 2005 6:36:55 PM

Archived from groups: rec.photo.digital (More info?)

Keith Sheppard wrote:

> I have been wondering whether the higher and higher print resolutions
> claimed by photo printer manufacturers are something of a con.
>
> My latest printer claims a resolution of 9600x2400 dpi. As a software
> developer, the first thing I tried to do was to drive the printer mysef,
> directly from my own code. I was therefore a little surprised when the
> device driver reported back a resolution of only 600dpi in each direction.
> In other words, the printer may be capable of up to 9600 different dots in a
> single inch but from software I can only specify 600 different colours to
> use for those dots. To look at it another way, that line of 9600 coloured
> dots actually comprises 600 segments each comprising 16 identically coloured
> dots.

What they are usually doing is using the addition dots per inch on the
paper to dither for intermediate colours using the available ink dots.

Concrete example
A 600dpi pixel rendered on a 9600x2400 dpi inkjet printer will contain
12x4 dots each of which in the simplest case can be CMYK. You
immediately have the potential to express 2^50 different dot patterns in
a single image pixel. It approximates the effect of continuous tone
colour more effectively. In practice they only use a fraction of the
possible dither patterns but it looks smoother even under magnification.

Regards,
Martin Brown
Anonymous
May 11, 2005 8:20:26 PM

Archived from groups: rec.photo.digital (More info?)

"Keith Sheppard" <keith.sheppard@tesco.net> wrote in message
news:Lpnge.2909$V%.2798@newsfe1-gui.ntli.net...
>I have been wondering whether the higher and higher print
> resolutions claimed by photo printer manufacturers are
> something of a con.
>
> My latest printer claims a resolution of 9600x2400 dpi. As a
> software developer, the first thing I tried to do was to drive the
> printer mysef, directly from my own code. I was therefore a
> little surprised when the device driver reported back a resolution
> of only 600dpi in each direction.

Correct. The printer driver resamples the image data to a fixed
600x600 pixel (!) per inch size, regardless what you send (assuming
high quality settings and photo paper). That data is further dithered
at higher resolution to represent intermediate colors. This allows to
represent more colors than possible with a few ink combinations on a
white(ish) background. The dithering is done by positioning variable
sized droplets of ink close to, or by mixing, or bleeding into, each
other. The dithering resolution is higher than human visual acuity can
resolve (so the color shades look like continuous tone prints), while
the 600 ppi resolution borders on (or exceeds) what human vision can
resolve (with the exception of particular patterns that trigger
Vernier acuity).

Bart
Anonymous
May 11, 2005 8:20:27 PM

Archived from groups: rec.photo.digital (More info?)

On Wed, 11 May 2005 16:20:26 +0200, "Bart van der Wolf"
<bvdwolf@no.spam> wrote:

>
>"Keith Sheppard" <keith.sheppard@tesco.net> wrote in message
>news:Lpnge.2909$V%.2798@newsfe1-gui.ntli.net...
>>I have been wondering whether the higher and higher print
>> resolutions claimed by photo printer manufacturers are
>> something of a con.
>>
>> My latest printer claims a resolution of 9600x2400 dpi. As a
>> software developer, the first thing I tried to do was to drive the
>> printer mysef, directly from my own code. I was therefore a
>> little surprised when the device driver reported back a resolution
>> of only 600dpi in each direction.
>
>Correct. The printer driver resamples the image data to a fixed
>600x600 pixel (!) per inch size, regardless what you send (assuming
>high quality settings and photo paper). That data is further dithered
>at higher resolution to represent intermediate colors. This allows to
>represent more colors than possible with a few ink combinations on a
>white(ish) background. The dithering is done by positioning variable
>sized droplets of ink close to, or by mixing, or bleeding into, each
>other. The dithering resolution is higher than human visual acuity can
>resolve (so the color shades look like continuous tone prints), while
>the 600 ppi resolution borders on (or exceeds) what human vision can
>resolve (with the exception of particular patterns that trigger
>Vernier acuity).

All true.

There is however, still a scam of sorts. That is; unless the dot is
small enough to be uniquely identifiable when printed at 9600x2400,
the quoted 'dithering' resolution can't be achieved. Paper obviously
has a big part to play in this equation. To the printer's advantage,
variable droplet size technology puts another mathematical spanner in
the works when trying to argue with numbers.

--
Owamanga!
http://www.pbase.com/owamanga
Anonymous
May 12, 2005 2:01:27 AM

Archived from groups: rec.photo.digital (More info?)

"Keith Sheppard" <keith.sheppard@tesco.net> schreef in
bericht news:Lpnge.2909$V%.2798@newsfe1-gui.ntli.net...
> I have been wondering whether the higher and higher print
resolutions
> claimed by photo printer manufacturers are something of a
con.
>
> My latest printer claims a resolution of 9600x2400 dpi.
As a software
> developer, the first thing I tried to do was to drive the
printer mysef,
> directly from my own code. I was therefore a little
surprised when the
> device driver reported back a resolution of only 600dpi in
each direction.
> In other words, the printer may be capable of up to 9600
different dots in a
> single inch but from software I can only specify 600
different colours to
> use for those dots. To look at it another way, that line
of 9600 coloured
> dots actually comprises 600 segments each comprising 16
identically coloured
> dots.
>

600 segments of 16 identically coloured dots make up 9600
dots.
The printer delivers the 9600 dpi.
So where is the - marketing con ?
Anonymous
May 12, 2005 6:03:19 AM

Archived from groups: rec.photo.digital (More info?)

"Owamanga" <owamanga(not-this-bit)@hotmail.com> wrote in message
news:4k54815k67v45stjbtsvnslitf2npqkt4u@4ax.com...
> On Wed, 11 May 2005 16:20:26 +0200, "Bart van der Wolf"
> <bvdwolf@no.spam> wrote:
>
>>
>>"Keith Sheppard" <keith.sheppard@tesco.net> wrote in message
>>news:Lpnge.2909$V%.2798@newsfe1-gui.ntli.net...
>>>I have been wondering whether the higher and higher print
>>> resolutions claimed by photo printer manufacturers are
>>> something of a con.
>>>
>>> My latest printer claims a resolution of 9600x2400 dpi. As a
>>> software developer, the first thing I tried to do was to drive the
>>> printer mysef, directly from my own code. I was therefore a
>>> little surprised when the device driver reported back a resolution
>>> of only 600dpi in each direction.
>>
>>Correct. The printer driver resamples the image data to a fixed
>>600x600 pixel (!) per inch size, regardless what you send (assuming
>>high quality settings and photo paper). That data is further
>>dithered
>>at higher resolution to represent intermediate colors. This allows
>>to
>>represent more colors than possible with a few ink combinations on a
>>white(ish) background. The dithering is done by positioning variable
>>sized droplets of ink close to, or by mixing, or bleeding into, each
>>other. The dithering resolution is higher than human visual acuity
>>can
>>resolve (so the color shades look like continuous tone prints),
>>while
>>the 600 ppi resolution borders on (or exceeds) what human vision can
>>resolve (with the exception of particular patterns that trigger
>>Vernier acuity).
>
> All true.
>
> There is however, still a scam of sorts. That is; unless the dot is
> small enough to be uniquely identifiable when printed at 9600x2400,
> the quoted 'dithering' resolution can't be achieved. Paper obviously
> has a big part to play in this equation. To the printer's advantage,
> variable droplet size technology puts another mathematical spanner
> in
> the works when trying to argue with numbers.

Sure, and I reluctantly tend to agree (consumer purchase decision
statistics apparently prove the manufacturers right), higher DPI (not
PPI) numbers sell better (to the uninitiated). However, discerning
600x600 PPI pixels still borders on the human visual acuity limit.
Different sources indicate that 8 lp/mm (=16 pixels/mm, or 406
pixels/inch), represents the average (I do better due to correction)
human visual resolution limit (assuming "normal" viewing distance of
about 10 inches and adequate luminance level) for continuous tone
images. Since diagonal resolution in a square grid is a factor of
Sqrt(2) higher (=575 PPI) in the diagonal dimension, 600 PPI for
Canon/HP printers (or 720 PPI for Epsons) seems adequate.

Bart
Anonymous
May 12, 2005 1:45:48 PM

Archived from groups: rec.photo.digital (More info?)

>>600 segments of 16 identically coloured dots make up 9600 dots.
>>The printer delivers the 9600 dpi.
>>So where is the - marketing con ?

The "con", or "misunderstanding", depending upon your point of view, is that
many people will automatically assume that higher dpi numbers mean a better
resolution of photograph. The average "man on the Clapham Omnibus" is
likely to assume that a 9600 dpi printer could, if asked politely by
software, render a line 1/9600" wide. I now see that ain't what it means.

I would like to thank the various respondents who have clarified the
difference between PPI and DPI. I now understand that the resolution
(applying the layman's loose definition of the term) of the printer and
associated drivers is actually 600 ppi. As Bart pointed out, this is almost
certainly adequate for my purposes.

To put it another way, the image which the software communicates to the
printer is at 600 pixels per inch resolution. Any detail which is smaller
than 1/600th of an inch (at the chosen image size) won't be visible in the
print, no matter what dpi figure the printer is capable of.

What I now realise is that the excess of dpi over ppi is not to improve
resolution, it is to improve the gamut of colours that can be rendered. I
know that not all dot patterns are used but it they were then, assuming 4
colour options (c/m/b/bk) per dot, that would give 16x16x4 different
"colours" for each pixel.

Now I understand what the salesman said when he told me that the higher
resolution of the newer printers obviates the need for Photo-cyan and
Photo-magenta ink cartridges.

Does that just about sum it up?

Keith
Anonymous
May 12, 2005 1:45:49 PM

Archived from groups: rec.photo.digital (More info?)

>>> In other words, the printer may be capable of up to 9600 different dots
in
>>> a
>>> single inch but from software I can only specify 600 different colours
to
>>> use for those dots.
>>
>>600 colours? Were did that come from?
Sorry, I am expressing myself badly. I don't mean a palette of 600
different colours. What I mean is that I can only send 600 different RGB
combinations to the driver to be reproduced in any one linear inch.

Thanks for the clarification on dpi vs. ppi. It took my dinosaur brain
several posts to get my head round it but I think it has now sunk in - see
my response to Ben Brugman.

Keith
Anonymous
May 12, 2005 1:45:50 PM

Archived from groups: rec.photo.digital (More info?)

Ken

Thanks for your detailed description which was extremely useful. It has
finally sunk in and I won't fall into that trap again. Unfortunately I
suspect that many further generations of naive users will fall into the same
trap, so keep that text for the next one!

I don't even think of myself as a newbie. I'm a software developer with
years of experience in what we used to call multimedia. I fully understand
colour rendition on a monitor - I just never stopped to think about
printers. I suppose my brain sort of assumed they were a bit like monitors
with streams of ink droplets replacing "cathode rays" (whatever they are - I
never understood hardware). It never occurred to me that the printer
couldn't vary the intensity of a drop.

I shall now think of my monitor as a piano and my printer as a harpsichord
(sorry - esoteric simile for the musicians) and I can't go wrong ;) 

Keith
Anonymous
May 12, 2005 2:30:33 PM

Archived from groups: rec.photo.digital (More info?)

In article <gBFge.1680$RJ6.868@newsfe1-win.ntli.net>,
keith.sheppard@tesco.net (Keith Sheppard) wrote:

> Does that just about sum it up?
Yes but you're not supposed to behave like this on Usenet. You're supposed
to call everyone idiots, claim you're right and everyone else is wrong,
threaten a lawsuit on the printer makers and then blame it all on
terrorists.

Reasoned responses succinctly summarising the responses and noting your
new found knowledge are simply not acceptable.


Iain
Anonymous
May 12, 2005 3:08:09 PM

Archived from groups: rec.photo.digital (More info?)

Bart van der Wolf wrote:
>
>
> Sure, and I reluctantly tend to agree (consumer purchase decision
> statistics apparently prove the manufacturers right), higher DPI (not
> PPI) numbers sell better (to the uninitiated). However, discerning
> 600x600 PPI pixels still borders on the human visual acuity limit.
> Different sources indicate that 8 lp/mm (=16 pixels/mm, or 406
> pixels/inch), represents the average (I do better due to correction)
> human visual resolution limit (assuming "normal" viewing distance of
> about 10 inches and adequate luminance level) for continuous tone
> images. Since diagonal resolution in a square grid is a factor of
> Sqrt(2) higher (=575 PPI) in the diagonal dimension, 600 PPI for
> Canon/HP printers (or 720 PPI for Epsons) seems adequate.
>
> Bart

Seems to me that the greater the ratio between dpi and ppi, the more
shades the printer can print, improving quality. Yeah, having more than
three or four inks helps, but ratio of dpi to ppi should help too.

That is, for real full-toned photography, not line drawings or 256 color
graphics. With most formats today allowing millions of colors, seems to
me we want the dither cell to have as many dots in it as possible,
without making the cell dimensions so large that we reduce ppi.
Anonymous
May 12, 2005 3:15:16 PM

Archived from groups: rec.photo.digital (More info?)

Keith Sheppard wrote:
> I would like to thank the various respondents who have clarified the
> difference between PPI and DPI. I now understand that the resolution
> (applying the layman's loose definition of the term) of the printer and
> associated drivers is actually 600 ppi. As Bart pointed out, this is almost
> certainly adequate for my purposes.
>
> To put it another way, the image which the software communicates to the
> printer is at 600 pixels per inch resolution. Any detail which is smaller
> than 1/600th of an inch (at the chosen image size) won't be visible in the
> print, no matter what dpi figure the printer is capable of.
>
> What I now realise is that the excess of dpi over ppi is not to improve
> resolution, it is to improve the gamut of colours that can be rendered. I
> know that not all dot patterns are used but it they were then, assuming 4
> colour options (c/m/b/bk) per dot, that would give 16x16x4 different
> "colours" for each pixel.
>
> Now I understand what the salesman said when he told me that the higher
> resolution of the newer printers obviates the need for Photo-cyan and
> Photo-magenta ink cartridges.
>
> Does that just about sum it up?
>
> Keith
>
>
It sums it up as long as we don't go further into defining resolution.
I used to get on a soap box about resolution meaning more than, or
something other than just the pixel pitch. I now find it okay to
consider pixel pitch (ppi) as ONE form of resolution.

However, coming from the film photo world and analog TV world, I still
prefer a definition of resolution that is a true, measured test of
visibility of detail- but that is a whole 'nother subject :-)
Anonymous
May 12, 2005 7:03:21 PM

Archived from groups: rec.photo.digital (More info?)

"Keith Sheppard" <keith.sheppard@tesco.net> wrote in message
news:iBFge.1682$RJ6.541@newsfe1-win.ntli.net...
SNIP
> Unfortunately I suspect that many further generations of naive users
> will fall into the same trap, so keep that text for the next one!

Not only the naive ones. There are many heated debates in various
forums/fora about the highest attainable resolution (and thus optimal
image input size with sharpening to the pixel) on inkjet printers. As
you have found out, the printer driver gets feedback about the optimal
PPI to send, given the choice of paper and quality settings.

Bart
Anonymous
May 12, 2005 11:50:55 PM

Archived from groups: rec.photo.digital (More info?)

[A complimentary Cc of this posting was sent to
Bart van der Wolf
<bvdwolf@no.spam>], who wrote in article <42829dd1$0$64739$e4fe514c@news.xs4all.nl>:
> Different sources indicate that 8 lp/mm (=16 pixels/mm, or 406
> pixels/inch), represents the average (I do better due to correction)
> human visual resolution limit (assuming "normal" viewing distance of
> about 10 inches and adequate luminance level) for continuous tone
> images. Since diagonal resolution in a square grid is a factor of
> Sqrt(2) higher (=575 PPI) in the diagonal dimension, 600 PPI for
> Canon/HP printers (or 720 PPI for Epsons) seems adequate.

My impression is that you got your sqrt(2) in a wrong place. If you
want to achieve 8 lp/mm in diagonal direction, you need to have the
square grid of 11 pixels/mm. So to cover the diagonal direction, you
need only 300 ppi. So 400 ppi covers both "orhtogonal" and "diagonal"
directions.

There ARE some flaws in my argument: e.g., it is "hard" to distinguish
*which* of two diagonal directions a checkerboard pattern represents.
;-) Anyway, *multiplying* by sqrt(2) is definitely wrong...

Hope this helps,
Ilya
Anonymous
May 13, 2005 12:03:58 AM

Archived from groups: rec.photo.digital (More info?)

[A complimentary Cc of this posting was sent to
Keith Sheppard
<keith.sheppard@tesco.net>], who wrote in article <gBFge.1680$RJ6.868@newsfe1-win.ntli.net>:
> What I now realise is that the excess of dpi over ppi is not to improve
> resolution, it is to improve the gamut of colours that can be rendered.

I think "gamut" is used in another sense (approximately: how close to
boundary of the "color triangle" can you get); this is more like
"color resolution": the resolution inside the gamut inside the "color
triangle".

> I know that not all dot patterns are used but it they were then,
> assuming 4 colour options (c/m/b/bk) per dot, that would give
> 16x16x4 different "colours" for each pixel.

I do not know how you got this value. Assuming that different color
dots can overlap, but no black, one gets 16 shades of each color, so
16*16*16. If they cannot overlap, then it is of order of magnitude
16*16*16/6 (actually more, binom(19,3)=969). I have no idea how black
is mixed into this...

Hope this helps,
Ilya
Anonymous
May 13, 2005 5:42:42 AM

Archived from groups: rec.photo.digital (More info?)

"Ilya Zakharevich" <nospam-abuse@ilyaz.org> wrote in message
news:D 60c2v$2cjf$1@agate.berkeley.edu...
SNIP
> My impression is that you got your sqrt(2) in a wrong place.

Try drawing a diagonal black and white pattern (like
http://www.xs4all.nl/~bvdwolf/temp/DiagRes.gif , zoom in to see the
diagonal lines), the densest diagonal pattern will have a sqrt(2)
cycle spacing, while in the horizontal or vertical direction it would
have a 2 pixel cycle spacing. The difference is a factor of sqrt(2)
higher density for the diagonal cycle pattern, or 1/sqrt(2) depending
on what you want to express (density or distance).

Bart
Anonymous
May 13, 2005 1:13:54 PM

Archived from groups: rec.photo.digital (More info?)

>>I think "gamut" is used in another sense (approximately: how close to
>>boundary of the "color triangle" can you get); this is more like
>>"color resolution": the resolution inside the gamut inside the "color
>>triangle".
There you go, you see. As a layman you try to use a perfectly ordinary
English word and some darned techie has hijacked it as a technical term with
a very specific meaning. My Pocket Oxford defines "gamut" as the "entire
range" - that's what I meant.

>>> I know that not all dot patterns are used but it they were then,
>>> assuming 4 colour options (c/m/b/bk) per dot, that would give
>>> 16x16x4 different "colours" for each pixel.

>>I do not know how you got this value.

It was based on the fact that if you have a 16x16 array of dots (it never
occurred to me that they might overlap), each of which can have one of four
different colour values, there are 16x16x4 different combinations. I put
the word "colours" in quotes because clearly many patterns will be perceived
as identical. For example, alternating cyan and magenta dots will probably
look much the same irrespective of whether you start with cyan or start with
magenta. Again, I am applying layman's logic to the situation and freely
admit to a total lack of detailed technical knowledge of the issues.

Keith
Anonymous
May 16, 2005 2:00:03 AM

Archived from groups: rec.photo.digital (More info?)

[A complimentary Cc of this posting was sent to
Bart van der Wolf
<bvdwolf@no.spam>], who wrote in article <4283e9f5$0$64738$e4fe514c@news.xs4all.nl>:
> > My impression is that you got your sqrt(2) in a wrong place.

> Try drawing a diagonal black and white pattern (like
....
> have a 2 pixel cycle spacing. The difference is a factor of sqrt(2)
> higher density for the diagonal cycle pattern

??? Eh? This is exactly what I said; but this contradicts what you
said in the grandparent (that you need sqrt(2) higher ppi value to
express the same cycles/mm in diagonal direction).

Hope this helps,
Ilya
Anonymous
May 16, 2005 2:05:46 AM

Archived from groups: rec.photo.digital (More info?)

[A complimentary Cc of this posting was sent to
Keith Sheppard
<keith.sheppard@tesco.net>], who wrote in article <md_ge.4914$he1.4215@newsfe6-gui.ntli.net>:
> >>I do not know how you got this value.

> It was based on the fact that if you have a 16x16 array of dots (it never
> occurred to me that they might overlap), each of which can have one of four
> different colour values, there are 16x16x4 different combinations.

Nope, it would be 4^(16*16) (which is a couple of hundreds of orders
of magnitude higher ;-). But actually, I think the array is 4x4, not
16x16, right? And there are *5* possible colors, not 4 (you forgot
about white ;-).

> magenta. Again, I am applying layman's logic to the situation and freely
> admit to a total lack of detailed technical knowledge of the issues.

Some of my estimates were also not good (but the binomial one is
fine). E.g., on a 4x4 square you can have 17 levels of a particular
color, not 16. (Those from 0 to 16.)

Yours,
Ilya
Anonymous
May 16, 2005 5:09:57 AM

Archived from groups: rec.photo.digital (More info?)

"Ilya Zakharevich" <nospam-abuse@ilyaz.org> wrote in message
news:D 68gp3$2u5k$1@agate.berkeley.edu...
> [A complimentary Cc of this posting was sent to
> Bart van der Wolf
> <bvdwolf@no.spam>], who wrote in article
> <4283e9f5$0$64738$e4fe514c@news.xs4all.nl>:
>> Try drawing a diagonal black and white pattern (like
>> ...
>> have a 2 pixel cycle spacing. The difference is a factor of
>> sqrt(2) higher density for the diagonal cycle pattern
>
> ??? Eh? This is exactly what I said;

Not really, but since you agee with me, why quibble.

> but this contradicts what you said in the grandparent (that
> you need sqrt(2) higher ppi value to express the same
> cycles/mm in diagonal direction).

No, I didn't say that, you get sqrt(2) higher PPI value in the
diagonal (asuming square pixels) dimension, whether you like it or
not.

> Hope this helps,

Not really, but as long as you agree, I guess yes.

Bart
Anonymous
May 16, 2005 7:45:21 AM

Archived from groups: rec.photo.digital (More info?)

[A complimentary Cc of this posting was sent to
Bart van der Wolf
<bvdwolf@no.spam>], who wrote in article <4287d6c4$0$64748$e4fe514c@news.xs4all.nl>:
> > you need sqrt(2) higher ppi value to express the same
> > cycles/mm in diagonal direction).
>
> No, I didn't say that, you get sqrt(2) higher PPI value in the
> diagonal (asuming square pixels) dimension, whether you like it or
> not.

I see: you think that when you look at your 2400 dpi printer with a
tilted head, it becomes 3000 dpi printer. ;-) If this assumption
holds, then what you say is indeed consistent.

But the ppi and dpi values I discussed are related to resolution in
horizontal/vertical direction.

Thanks,
Ilya
Anonymous
May 17, 2005 1:43:22 AM

Archived from groups: rec.photo.digital (More info?)

"Ilya Zakharevich" <nospam-abuse@ilyaz.org> wrote in message
news:D 6950h$5sd$1@agate.berkeley.edu...
SNIP
> But the ppi and dpi values I discussed are related to resolution in
> horizontal/vertical direction.

Then we seem to be talking about different diagonal resolution ...

Bart
!