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Manipulate the DPI with cfimage?
Author: Mark Kruger
Short Link: http://www.houseoffusion.com/groups/cf-talk/thread.cfm/threadid:54696#295791
Claude,
Thanks for an enlightening foray into the world of graphics. I especially
like the part about a virtual object having no size..fascinating. It made me
think to myself... If a virtual tree falls in the woods... (ha).
In any case, excellent stuff. I feel edicated enough to be able to say now
with certainty that I know next to nothing about working with graphics :)
-Mark
>>Visually DPI represents "dots per inch" - it's a measure of "density" in
printing. The higher the DPI the better the quality of printing - right?
Exact. It's a density. The definition of a "resolution" is "the size of the
smallest element the instrument can measure,
-- if the instrument sees or measures things -- or generate, if the
instrument creates things.
It is closely related to the density, of course, but it is not formerly the
same thing.
Thus, the unit of resolution for instruments like printers, monitors or
scanners would be in inches, or 1/1000 In. For instance, a printer with a
density of 1000 DPI has a density of 1/1000 In.
Note that on some optical instruments like cameras, or human eye, the
resolution is measured in angle units. The human eye has a resolution of
about 1 minute angle.
>>On a monitor the "pixel" is in one way a measurement of size - as in
"how
many pixels can I get on the screen".
Ok, now "how many pixels", this is called the "definition". This is the
maximum number of different elements the instrument can measure or genrate
(ie: lines in TV transmission) Of course, the more pixels you have to
represent an image, the better the quality will be.
Note that:
density = definition / size of the working area resolution = size of the
working area / definition then density = 1 / resolution
>>When I look at an image in Fireworks I get a measurement of pixels at
the
bottom - 800 by 600 for example - 96 "pixels per inch". That's a size
measurement.
For the pixels, yes, but one should never should forget that it is a virtual
image.
Normally, a virtual object has no size.
Now, if you make a physical representation of your virtual image, it becomes
a real image, and its size will be nb.pixels * resolution of the printer, or
nb.pixels / density of the printer.
Talking of pixels per inch in a virtual image just does not make sense.
Where are the inches we are talking about ?
>>This setting (as I understand it) is really related to the lossy
compression that is used and dictates how aggressively the file is to be
compressed.
Exact, and it has nothing to do with pixels, or density.
>>But this is where non-imagy folks like me get confused. I DPI is not the
same as "resolution" what is the proper term?
In my book it is "density".
>> Is it "bit depth" or the number of colors used or what.
Yes, it is the numbers of bits used to express color, thus the magnitude of
the numbers that can be used to express the color. Then one should finally
call it the "color definition".
>>How do you reference the quality of the image on the screen without
using
the word "resolution"? And if resolution IS the proper term for the
"quality" of an image, then doesn't it have at least some correlation to
DPI?
You cannot express the quality in DPI or any other kind of unit.
The quality depends on many factors like the pixel definition, the color
definition, the compression level the precision and fidelity of the display
or printing equipment, and finally, the quality of your own eye !
The overall quality is a chain of elements, DPI is only one of them.
>>I need education on this point. What is the proper way of referring to
the "quality" of a digital image?
There is no really a unit to measure "quality", one only can take in account
the quality of each element in the chain.
Just like in a old analogic sound equipment, the overall quality depends on
many element, from the musical instrument to the auditor's ear, including
the recording system, the vinyl record pressing, the piezzo pick-up, the
speaker system, etc.
Author: Claude Schneegans
Short Link: http://www.houseoffusion.com/groups/cf-talk/thread.cfm/threadid:54696#295771
>>Ok.... So "compression" is the best measure of quality?
... except that it is a reverse measure: the higher the compression is,
the lower the quality.
Some softwares use % compression, some others % in quality.
A 10% compressed image is equivalent to a 90% quality, etc.
--
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Thanks.
Author: Claude Schneegans
Short Link: http://www.houseoffusion.com/groups/cf-talk/thread.cfm/threadid:54696#295770
>>I think Claude's usage of the term "density" is an excellent choice.
Humbly, it's not really my choice, this is the way I learned it when I
was student in physics.
I just hope the translation is correct, in French, we call it "densité" ;-)
--
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Thanks.
Author: Claude Schneegans
Short Link: http://www.houseoffusion.com/groups/cf-talk/thread.cfm/threadid:54696#295769
>>Visually DPI represents "dots per inch" - it's a measure of "density" in
printing. The higher the DPI the better the quality of printing - right?
Exact. It's a density. The definition of a "resolution" is "the size of
the smallest element the instrument can measure,
-- if the instrument sees or measures things -- or generate, if the
instrument creates things.
It is closely related to the density, of course, but it is not formerly
the same thing.
Thus, the unit of resolution for instruments like printers, monitors or
scanners would be in inches,
or 1/1000 In. For instance, a printer with a density of 1000 DPI has a
density of 1/1000 In.
Note that on some optical instruments like cameras, or human eye, the
resolution is measured
in angle units. The human eye has a resolution of about 1 minute angle.
>>On a monitor the "pixel" is in one way a measurement of size - as in
"how
many pixels can I get on the screen".
Ok, now "how many pixels", this is called the "definition". This is the
maximum number of different elements
the instrument can measure or genrate (ie: lines in TV transmission)
Of course, the more pixels you have to represent an image, the better
the quality will be.
Note that:
density = definition / size of the working area
resolution = size of the working area / definition
then density = 1 / resolution
>>When I look at an image in Fireworks I
get a measurement of pixels at the bottom - 800 by 600 for example - 96
"pixels per inch". That's a size measurement.
For the pixels, yes, but one should never should forget that it is a
virtual image.
Normally, a virtual object has no size.
Now, if you make a physical representation of your virtual image, it
becomes a real image,
and its size will be nb.pixels * resolution of the printer,
or nb.pixels / density of the printer.
Talking of pixels per inch in a virtual image just does not make sense.
Where are the inches we are talking about ?
>>This setting (as I understand it) is really
related to the lossy compression that is used and dictates how aggressively
the file is to be compressed.
Exact, and it has nothing to do with pixels, or density.
>>But this is where non-imagy folks like me get confused. I DPI is not the
same as "resolution" what is the proper term?
In my book it is "density".
>> Is it "bit depth" or the number of colors used or what.
Yes, it is the numbers of bits used to express color, thus the magnitude
of the numbers that can be used
to express the color. Then one should finally call it the "color
definition".
>>How do you reference the quality of the image
on the screen without using the word "resolution"? And if resolution IS the
proper term for the "quality" of an image, then doesn't it have at least
some correlation to DPI?
You cannot express the quality in DPI or any other kind of unit.
The quality depends on many factors like the pixel definition, the color
definition, the compression level
the precision and fidelity of the display or printing equipment, and
finally, the quality of your own eye !
The overall quality is a chain of elements, DPI is only one of them.
>>I need education on this point. What is the proper way of referring
to the
"quality" of a digital image?
There is no really a unit to measure "quality", one only can take in
account the quality of each
element in the chain.
Just like in a old analogic sound equipment, the overall quality depends
on many element, from
the musical instrument to the auditor's ear, including the recording
system, the vinyl record pressing,
the piezzo pick-up, the speaker system, etc.
--
_______________________________________
REUSE CODE! Use custom tags;
See http://www.contentbox.com/claude/customtags/tagstore.cfm
(Please send any spam to this address: piegeacon@internetique.com)
Thanks.
Author: Rick Root
Short Link: http://www.houseoffusion.com/groups/cf-talk/thread.cfm/threadid:54696#295767
> Ok.... So "compression" is the best measure of quality?
Yes, in a world of compressed images.
However, your average print shop would rarely used compressed graphics
for printed material.
"dots per inch" is a reasonable measure of quality when you consider
that you're taking a 2100x1500 image and printing it in the space of
7"x5" (300dpi) or 14"x10" (150 dpi).. keeping in mind that the
halftone screen used for high quality printing aren't usually much
over 150 lines per inch.
"dpi" is merely a representation of actual pixels to the space
allotted for printing or viewing those pixels.. so "density" is a
pretty good word.
For a fun read:
http://en.wikipedia.org/wiki/Halftone
--
Rick Root
Check out CFMBB, BlogCFM, ImageCFC, ImapCFC, CFFM, and more at
www.opensourcecf.com
Author: Mark Kruger
Short Link: http://www.houseoffusion.com/groups/cf-talk/thread.cfm/threadid:54696#295765
Ok.... So "compression" is the best measure of quality?
Mark...
You're also confusing image quality (compression) with DPI (or pixel
dimensions). At it's heart, a bitmapped (or raster) image, is simply a
series of 1 pixels blocks with specific color assignments. An image doesn't
know what quality (compression) it is. It also doesn't know what resolution
it is. The only thing an image knows about itself, is how many pixels it is
comprised of, and what specific color each of those pixels are.
I think Claude's usage of the term "density" is an excellent choice. DPI
simply indicates how many pixels are crammed into your unit of measure. If
you REALLY want to start bending your head you'd start talking LPI (lines
per inch), or linescreen. That's usually a better measure of print quality
than is DPI.
Bit depth simply refers to the total number of colors available to an image.
Claude,
Hmmm.... Ok this is interesting to me. The argument below seems semantic....
So I think I am missing something. I'd like to get my head around this.
Visually DPI represents "dots per inch" - it's a measure of "density" in
printing. The higher the DPI the better the quality of printing - right?
Ok I get that so far....
On a monitor the "pixel" is in one way a measurement of size - as in "how
many pixels can I get on the screen". When I look at an image in Fireworks I
get a measurement of pixels at the bottom - 800 by 600 for example - 96
"pixels per inch". That's a size measurement.
But on a screen or inside the file - what is representative of the "quality"
of the file as it is presented on a monitor... In a JPG file there is a
"quality" setting for exporting. This setting (as I understand it) is really
related to the lossy compression that is used and dictates how aggressively
the file is to be compressed.
But this is where non-imagy folks like me get confused. I DPI is not the
same as "resolution" what is the proper term? Is it "bit depth" or the
number of colors used or what. How do you reference the quality of the image
on the screen without using the word "resolution"? And if resolution IS the
proper term for the "quality" of an image, then doesn't it have at least
some correlation to DPI?
In my head a JPG is still a group of pixels - a bitmap... (even though I
know it is more than that). I envision that the smaller the pixels are and
the closer they are packed tightly together - the better the "resolution" of
the picture - yes? So in my head, DPI and JPG's pixels have a similar
function.
I need education on this point. What is the proper way of referring to the
"quality" of a digital image? Camera's use "mega-pixels" ... But doesn't
that mean smaller pixels packed "closer" together? Isn't it analogous to
having 180 pixels per inch instead of just 96 pixels per inch? And doesn't
that translate pretty well into the idea of "density"?
Help out a struggling graphically challenged coder :)
-mark
Mark A. Kruger, CFG, MCSE
(402) 408-3733 ext 105
www.cfwebtools.com
www.coldfusionmuse.com
www.necfug.com
>>I've argued many times myself (as author of ImageCFC) that "DPI" is not
a
function of the image itself, but the meta-data of the image, as the DPI is
*ONLY* used for print.
...... or scanning, I couldn't agree more.
The resolution is a quality of instruments, images have no resolution.
...... and DPI do not even express a "resolution" as currently said, but a
"density", anyway... ;-)
Author: Andy Matthews
Short Link: http://www.houseoffusion.com/groups/cf-talk/thread.cfm/threadid:54696#295764
Mark...
You're also confusing image quality (compression) with DPI (or pixel
dimensions). At it's heart, a bitmapped (or raster) image, is simply a
series of 1 pixels blocks with specific color assignments. An image doesn't
know what quality (compression) it is. It also doesn't know what resolution
it is. The only thing an image knows about itself, is how many pixels it is
comprised of, and what specific color each of those pixels are.
I think Claude's usage of the term "density" is an excellent choice. DPI
simply indicates how many pixels are crammed into your unit of measure. If
you REALLY want to start bending your head you'd start talking LPI (lines
per inch), or linescreen. That's usually a better measure of print quality
than is DPI.
Bit depth simply refers to the total number of colors available to an image.
Claude,
Hmmm.... Ok this is interesting to me. The argument below seems semantic....
So I think I am missing something. I'd like to get my head around this.
Visually DPI represents "dots per inch" - it's a measure of "density" in
printing. The higher the DPI the better the quality of printing - right?
Ok I get that so far....
On a monitor the "pixel" is in one way a measurement of size - as in "how
many pixels can I get on the screen". When I look at an image in Fireworks I
get a measurement of pixels at the bottom - 800 by 600 for example - 96
"pixels per inch". That's a size measurement.
But on a screen or inside the file - what is representative of the "quality"
of the file as it is presented on a monitor... In a JPG file there is a
"quality" setting for exporting. This setting (as I understand it) is really
related to the lossy compression that is used and dictates how aggressively
the file is to be compressed.
But this is where non-imagy folks like me get confused. I DPI is not the
same as "resolution" what is the proper term? Is it "bit depth" or the
number of colors used or what. How do you reference the quality of the image
on the screen without using the word "resolution"? And if resolution IS the
proper term for the "quality" of an image, then doesn't it have at least
some correlation to DPI?
In my head a JPG is still a group of pixels - a bitmap... (even though I
know it is more than that). I envision that the smaller the pixels are and
the closer they are packed tightly together - the better the "resolution" of
the picture - yes? So in my head, DPI and JPG's pixels have a similar
function.
I need education on this point. What is the proper way of referring to the
"quality" of a digital image? Camera's use "mega-pixels" ... But doesn't
that mean smaller pixels packed "closer" together? Isn't it analogous to
having 180 pixels per inch instead of just 96 pixels per inch? And doesn't
that translate pretty well into the idea of "density"?
Help out a struggling graphically challenged coder :)
-mark
Mark A. Kruger, CFG, MCSE
(402) 408-3733 ext 105
www.cfwebtools.com
www.coldfusionmuse.com
www.necfug.com
>>I've argued many times myself (as author of ImageCFC) that "DPI" is not
a
function of the image itself, but the meta-data of the image, as the DPI is
*ONLY* used for print.
..... or scanning, I couldn't agree more.
The resolution is a quality of instruments, images have no resolution.
..... and DPI do not even express a "resolution" as currently said, but a
"density", anyway... ;-)
Author: Mark Kruger
Short Link: http://www.houseoffusion.com/groups/cf-talk/thread.cfm/threadid:54696#295760
Claude,
Hmmm.... Ok this is interesting to me. The argument below seems semantic....
So I think I am missing something. I'd like to get my head around this.
Visually DPI represents "dots per inch" - it's a measure of "density" in
printing. The higher the DPI the better the quality of printing - right?
Ok I get that so far....
On a monitor the "pixel" is in one way a measurement of size - as in "how
many pixels can I get on the screen". When I look at an image in Fireworks I
get a measurement of pixels at the bottom - 800 by 600 for example - 96
"pixels per inch". That's a size measurement.
But on a screen or inside the file - what is representative of the "quality"
of the file as it is presented on a monitor... In a JPG file there is a
"quality" setting for exporting. This setting (as I understand it) is really
related to the lossy compression that is used and dictates how aggressively
the file is to be compressed.
But this is where non-imagy folks like me get confused. I DPI is not the
same as "resolution" what is the proper term? Is it "bit depth" or the
number of colors used or what. How do you reference the quality of the image
on the screen without using the word "resolution"? And if resolution IS the
proper term for the "quality" of an image, then doesn't it have at least
some correlation to DPI?
In my head a JPG is still a group of pixels - a bitmap... (even though I
know it is more than that). I envision that the smaller the pixels are and
the closer they are packed tightly together - the better the "resolution" of
the picture - yes? So in my head, DPI and JPG's pixels have a similar
function.
I need education on this point. What is the proper way of referring to the
"quality" of a digital image? Camera's use "mega-pixels" ... But doesn't
that mean smaller pixels packed "closer" together? Isn't it analogous to
having 180 pixels per inch instead of just 96 pixels per inch? And doesn't
that translate pretty well into the idea of "density"?
Help out a struggling graphically challenged coder :)
-mark
Mark A. Kruger, CFG, MCSE
(402) 408-3733 ext 105
www.cfwebtools.com
www.coldfusionmuse.com
www.necfug.com
>>I've argued many times myself (as author of ImageCFC) that "DPI" is not
a
function of the image itself, but the meta-data of the image, as the DPI is
*ONLY* used for print.
.... or scanning, I couldn't agree more.
The resolution is a quality of instruments, images have no resolution.
.... and DPI do not even express a "resolution" as currently said, but a
"density", anyway... ;-)
Author: Claude Schneegans
Short Link: http://www.houseoffusion.com/groups/cf-talk/thread.cfm/threadid:54696#295757
>>I've argued many times myself (as author of ImageCFC) that "DPI" is
not a function of the image itself, but the meta-data of the image, as
the DPI is *ONLY* used for print.
... or scanning, I couldn't agree more.
The resolution is a quality of instruments, images have no resolution.
... and DPI do not even express a "resolution" as currently said, but a
"density", anyway... ;-)
Author: Rick Root
Short Link: http://www.houseoffusion.com/groups/cf-talk/thread.cfm/threadid:54696#295741
> When you're dealing with images for display on computer screens, there's
> really no such thing as dpi. It all has to do with the pixel dimensions.
I've argued many times myself (as author of ImageCFC) that "DPI" is
not a function of the image itself, but the meta-data of the image, as
the DPI is *ONLY* used for print.
So unless you're using Coldfusion to send a file to the printer after
manipulating the "dpi", there's no point.
that being said.. if you've got a jpeg that has the meta data for DPI,
you could theoretically change the metadata to say that the image is
300 dpi, and when you open it in photoshop, it would be 300 dpi.
But as was said, the DPI has nothing to do with the image itself, so
if you've got an image with no meta data, you'd have to first convert
it to a format that supported image metadata, add thei mage metadata
and set the DPI.
--
Rick Root
Coldfusion/Flex Developer needed in Durham, full-time, no
telecommuters. Please email me! No third parties.
Author: Andy Matthews
Short Link: http://www.houseoffusion.com/groups/cf-talk/thread.cfm/threadid:54696#295737
When you're dealing with images for display on computer screens, there's
really no such thing as dpi. It all has to do with the pixel dimensions.
If you have a 1600x1200 image, then it would be 22in x 16in at 72dpi (on a
monitor) or 5in x 4in at 300dpi.
Hello,
i use a Linux Server with CF8 an want to read out or manipulate the dpi of
pictures with cfimage. I have found it only in the function
ImageGetEXIFMetaData, but not every picture have the Exif Data.
Is it right, that this function is not supported in CF8?
Thanks!
Carsten
Author: Carsten Klement
Short Link: http://www.houseoffusion.com/groups/cf-talk/thread.cfm/threadid:54696#295735
Hello,
i use a Linux Server with CF8 an want to read out or manipulate the dpi of
pictures with cfimage. I have found it only in the function ImageGetEXIFMetaData,
but not every picture have the Exif Data.
Is it right, that this function is not supported in CF8?
Thanks!
Carsten
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May 24, 2012
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