Resolution
Posted 22/07/2012 - 21:26
Link
Algernon wrote:
The Scantips site is probably more reliable than the Wikipedia article.
Well actually, Algi, you were the one who introduced the Wikipedia link.The Scantips site is probably more reliable than the Wikipedia article.
Moreover:
The Scantips author does not appear to know the difference between PPI and DPI. He does seem to concentrate on the monitor and printer - and ignore the graphics processor capability.
I know that the Windows resolution settings (in PPI, please note) are much cruder than those used by Apple, but either system offers a range of PPI settings regardless of the monitor. Even the fixed monitor built in to my G5 IMac has a choice of resolutions available in PPI.
Let me just quote a little bit from the rules of my Club:
Digital Projections submitted should be 8bit JPEG and at a resolution of 72 pixels/inch (so that entries may be e-mailed).RGB Mode and sRGB Colour Space.
1400 x 1050 pixels Landscape. Max height of portrait to be 1050 pixels.
You may note that the resolution is specified in PPI. An image to these rules projects quite well so as to fill a large projection screen. If printed (do note the IF), the size of a typical image would be 19.5 x 14.5 INCHES. A DPI value does not yet come into it, until I choose the (printed) image quality.
Water can wear away a stone - but it can't cook lunch
X-5
istDS
K2000
P50.
Lenses Digital: 50-200, 18-55 KAF: 28-80.
Lenses KA & K: SMC-KA f2.0, SMC-K f1.4, SMC-K f1.7 Tokina KA 28-70 , SMC Pentax 70-210 F4, Sigma KA 75-300 , Hanimex 500mm Mirror, and the Tamron Adaptall-2 stuff.
and then there's all the M42 kit, and the accessories ...
X-5
istDS
K2000
P50.
Lenses Digital: 50-200, 18-55 KAF: 28-80.
Lenses KA & K: SMC-KA f2.0, SMC-K f1.4, SMC-K f1.7 Tokina KA 28-70 , SMC Pentax 70-210 F4, Sigma KA 75-300 , Hanimex 500mm Mirror, and the Tamron Adaptall-2 stuff.
and then there's all the M42 kit, and the accessories ...
Posted 22/07/2012 - 22:09
Link
DoctorJeff wrote:
Digital Projections submitted should be 8bit JPEG and at a resolution of 72 pixels/inch (so that entries may be e-mailed).RGB Mode and sRGB Colour Space.
1400 x 1050 pixels Landscape. Max height of portrait to be 1050 pixels.
Surely the 'pixels/inch' bit is irrelevant. It will make bugger all difference to the file size . The key information is 1400 x 1050 pixels, ensuring the image will be at a sufficient resolution for the intended use.Digital Projections submitted should be 8bit JPEG and at a resolution of 72 pixels/inch (so that entries may be e-mailed).RGB Mode and sRGB Colour Space.
1400 x 1050 pixels Landscape. Max height of portrait to be 1050 pixels.
I've 'scanned over' the scantips article - it doesn't seem particularly relevant, as it's all to do with scanning. An 8x6 print scanned at 72ppi is obviously going to be pretty useless if you intend to print it....
Posted 22/07/2012 - 22:21
Link
http://www.rideau-info.com/photos/mythdpi.html
Quote:
If the pixels of an image do not change, then it has the same digital resolution no matter what number is parked in the DPI/PPI setting of the photo. One factor in the quality of printing to paper is many pixels per inch are delivered to the printer, a number between 200 and 300 is generally accepted to represent "photographic quality" at an arm's length viewing distance. But that quality, the PPI, is determined by how many pixels the image has - not the number parked in the DPI/PPI setting section.
Part of the confusion (and the myth) is generated by the fact that the PPI setting can (and is by some) used to determine the print size on virtual paper. It's often how graphic artists use photo programs, to virtually print size the photo. This has led to the erroneous view that this setting controls the resolution of the digital photo itself. But a digital photo's resolution are its pixels and if those don't change, the photo remains the same resolution.
The DPI/PPI number in the photo is simply a convenient at times conversion factor. Printing on all of today's home printers and most modern commercial printers involves remapping the photo, converting the pixels of the photo into printed dots. This isn't done on a one to one basis, one pixel does not equal one printer dot.
If the pixels of an image do not change, then it has the same digital resolution no matter what number is parked in the DPI/PPI setting of the photo. One factor in the quality of printing to paper is many pixels per inch are delivered to the printer, a number between 200 and 300 is generally accepted to represent "photographic quality" at an arm's length viewing distance. But that quality, the PPI, is determined by how many pixels the image has - not the number parked in the DPI/PPI setting section.
Part of the confusion (and the myth) is generated by the fact that the PPI setting can (and is by some) used to determine the print size on virtual paper. It's often how graphic artists use photo programs, to virtually print size the photo. This has led to the erroneous view that this setting controls the resolution of the digital photo itself. But a digital photo's resolution are its pixels and if those don't change, the photo remains the same resolution.
The DPI/PPI number in the photo is simply a convenient at times conversion factor. Printing on all of today's home printers and most modern commercial printers involves remapping the photo, converting the pixels of the photo into printed dots. This isn't done on a one to one basis, one pixel does not equal one printer dot.
Posted 23/07/2012 - 00:13
Link
You can find the answer to this by setting inappropriate values and seeing what happens.
Let's start with the camera, say a K20D, which has a native value of 72ppi. If we print this as it is we will get a huge print with very low resolution. It might look fine from a long distance away, but at normal distances with only 72 pixels for every inch it will be very pixelated.
So we change it for printing to 300ppi, which reduces the image size and means that each inch on the print now is made up of 300 pixels, a much more detailed image that we can view much closer.
I haven't looked up the exact values, but for this description that doesn't matter.
Now we get to our printer. If we take the 300ppi image and print it, the image is reproduced out of dots of ink. These are "dithered" to make a better continuous tone. But how may diots of ink will make up each inch of our image? Obviously the more the better. So I set my printer to reproduce the 300 pixels in my inch of image by laying down 2880 dots per inch. Each pixel is therefore made up of many dots, which makes the image look better.
Does that help?
Let's start with the camera, say a K20D, which has a native value of 72ppi. If we print this as it is we will get a huge print with very low resolution. It might look fine from a long distance away, but at normal distances with only 72 pixels for every inch it will be very pixelated.
So we change it for printing to 300ppi, which reduces the image size and means that each inch on the print now is made up of 300 pixels, a much more detailed image that we can view much closer.
I haven't looked up the exact values, but for this description that doesn't matter.
Now we get to our printer. If we take the 300ppi image and print it, the image is reproduced out of dots of ink. These are "dithered" to make a better continuous tone. But how may diots of ink will make up each inch of our image? Obviously the more the better. So I set my printer to reproduce the 300 pixels in my inch of image by laying down 2880 dots per inch. Each pixel is therefore made up of many dots, which makes the image look better.
Does that help?
Best regards, John
Posted 23/07/2012 - 10:14
Link
Quite a lot of that page is either confusing or incorrect, but he has described the printing of a single DOT quite well...
"The rated DPI of many home ink-jet printers is in the +1,000 range -
the caveat with this number is that it represents a blended dot
(overprinting a single "dot" with different colours to create
the colour that is needed)."
It was better when the printer manufacturer left out all the marketing
speak and just gave us a choice of BEST : NORMAL : EVERYDAY :
FASTDRAFT
We aren't interested in how many times they can over-spray a single
DOT with ink and at what distance apart their micro-dots are
"The rated DPI of many home ink-jet printers is in the +1,000 range -
the caveat with this number is that it represents a blended dot
(overprinting a single "dot" with different colours to create
the colour that is needed)."
It was better when the printer manufacturer left out all the marketing
speak and just gave us a choice of BEST : NORMAL : EVERYDAY :
FASTDRAFT
We aren't interested in how many times they can over-spray a single
DOT with ink and at what distance apart their micro-dots are
Half Man... Half Pentax ... Half Cucumber
Pentax K-1 + K-5 and some other stuff
Algi
Pentax K-1 + K-5 and some other stuff
Algi
Posted 23/07/2012 - 10:40
Link
Some of you might find the following information from MS
useful. It relates to Direct2D programming.
"The term dots derives from printing, where physical dots of ink are put onto paper.
For computer displays, it would be more accurate to say 96 pixels
per logical inch, but the term DPI has stuck."
Note Windows uses pixels per logical inch (DPI) for text and scales up or down
to suit the width of the screen. Exact pixels per inch isn't
used or catered for. Fonts can be scaled in Control Panel.
MS_Link
Adobe seem to be responsible for some of the confusion... they
use ppi .... Corel and a lot of other companies use dpi
-
useful. It relates to Direct2D programming.
"The term dots derives from printing, where physical dots of ink are put onto paper.
For computer displays, it would be more accurate to say 96 pixels
per logical inch, but the term DPI has stuck."
Note Windows uses pixels per logical inch (DPI) for text and scales up or down
to suit the width of the screen. Exact pixels per inch isn't
used or catered for. Fonts can be scaled in Control Panel.
MS_Link
Adobe seem to be responsible for some of the confusion... they
use ppi .... Corel and a lot of other companies use dpi
-
Half Man... Half Pentax ... Half Cucumber
Pentax K-1 + K-5 and some other stuff
Algi
Pentax K-1 + K-5 and some other stuff
Algi
Posted 23/07/2012 - 12:51
Link
Algernon wrote:
... Note Windows uses pixels per logical inch (DPI) for text and scales up or down to suit the width of the screen. Exact pixels per inch isn't used or catered for. Fonts can be scaled in Control Panel.
Adobe seem to be responsible for some of the confusion... they use ppi .... Corel and a lot of other companies use dpi -
So it would really be the case that Microsoft have caused the confusion between DPI and PPI by their choice of an existing term to replace another existing term.... Note Windows uses pixels per logical inch (DPI) for text and scales up or down to suit the width of the screen. Exact pixels per inch isn't used or catered for. Fonts can be scaled in Control Panel.
Adobe seem to be responsible for some of the confusion... they use ppi .... Corel and a lot of other companies use dpi -
They have done this in other places, notably by assigning a file extension to a program when that extension was already in use by another program. This can result in the best error message that I have ever seen - click on one of the original files to use that extension and get:
ERROR, the operation completed satisfactorily.
when, of course, it had failed to do so.
I used this example for years when teaching on a software engineering course.
Geoff
Water can wear away a stone - but it can't cook lunch
X-5
istDS
K2000
P50.
Lenses Digital: 50-200, 18-55 KAF: 28-80.
Lenses KA & K: SMC-KA f2.0, SMC-K f1.4, SMC-K f1.7 Tokina KA 28-70 , SMC Pentax 70-210 F4, Sigma KA 75-300 , Hanimex 500mm Mirror, and the Tamron Adaptall-2 stuff.
and then there's all the M42 kit, and the accessories ...
X-5
istDS
K2000
P50.
Lenses Digital: 50-200, 18-55 KAF: 28-80.
Lenses KA & K: SMC-KA f2.0, SMC-K f1.4, SMC-K f1.7 Tokina KA 28-70 , SMC Pentax 70-210 F4, Sigma KA 75-300 , Hanimex 500mm Mirror, and the Tamron Adaptall-2 stuff.
and then there's all the M42 kit, and the accessories ...
Posted 23/07/2012 - 12:51
Link
johnriley wrote:
Let's start with the camera, say a K20D, which has a native value of 72ppi. If we print this as it is we will get a huge print with very low resolution. It might look fine from a long distance away, but at normal distances with only 72 pixels for every inch it will be very pixelated.
But when you set the image to print at, say A3, the printer will map the image to fit it to that paper size (unless you print at 100%). We've established that a K5 image has enough pixels to provide the printer with about 300PPI at A3 so why not simply send it to print, selecting A3 as the output size? Let's start with the camera, say a K20D, which has a native value of 72ppi. If we print this as it is we will get a huge print with very low resolution. It might look fine from a long distance away, but at normal distances with only 72 pixels for every inch it will be very pixelated.
Algernon wrote:
We aren't interested in how many times they can over-spray a single
DOT with ink and at what distance apart their micro-dots are
That's for sure, Algi!
We aren't interested in how many times they can over-spray a single
DOT with ink and at what distance apart their micro-dots are
Posted 23/07/2012 - 21:02
Link
Pentaxophile wrote:
Well, you would think that was the case. I had never bothered with the 72PPI since I have always handed my entries in on a memory stick. So, before I sent an e-mail winging its way to our Comp. Sec., I did a quick test.DoctorJeff wrote:
Digital Projections submitted should be 8bit JPEG and at a resolution of 72 pixels/inch (so that entries may be e-mailed).RGB Mode and sRGB Colour Space.
1400 x 1050 pixels Landscape. Max height of portrait to be 1050 pixels.
Surely the 'pixels/inch' bit is irrelevant. It will make bugger all difference to the file size . The key information is 1400 x 1050 pixels ....Digital Projections submitted should be 8bit JPEG and at a resolution of 72 pixels/inch (so that entries may be e-mailed).RGB Mode and sRGB Colour Space.
1400 x 1050 pixels Landscape. Max height of portrait to be 1050 pixels.
An original image straight from my K20 in "Best quality" JPEG
10.7 Mb
An original image straight from my K20 in "Best quality", resized to 1400 x 1050 pix
1.7 Mb
An original image straight from my K20 in "Best quality", resized to 1400 x 1050 pix at 72PPI
540 Kb
Now, to me, that is not exactly what you would call "bugger all difference". Resizing was done in PS Elements 10. No other PP was applied. And yes, I have the original DNG file as well (I always shoot RAW + JPEG).
Geoff
Water can wear away a stone - but it can't cook lunch
X-5
istDS
K2000
P50.
Lenses Digital: 50-200, 18-55 KAF: 28-80.
Lenses KA & K: SMC-KA f2.0, SMC-K f1.4, SMC-K f1.7 Tokina KA 28-70 , SMC Pentax 70-210 F4, Sigma KA 75-300 , Hanimex 500mm Mirror, and the Tamron Adaptall-2 stuff.
and then there's all the M42 kit, and the accessories ...
X-5
istDS
K2000
P50.
Lenses Digital: 50-200, 18-55 KAF: 28-80.
Lenses KA & K: SMC-KA f2.0, SMC-K f1.4, SMC-K f1.7 Tokina KA 28-70 , SMC Pentax 70-210 F4, Sigma KA 75-300 , Hanimex 500mm Mirror, and the Tamron Adaptall-2 stuff.
and then there's all the M42 kit, and the accessories ...
Posted 23/07/2012 - 21:20
Link
Thanks Geoff, that's an excellent lesson is simply following submission requirements!
Best regards, John
Posted 23/07/2012 - 21:25
Link
Quote:
But when you set the image to print at, say A3, the printer will map the image to fit it to that paper size (unless you print at 100%). We've established that a K5 image has enough pixels to provide the printer with about 300PPI at A3 so why not simply send it to print, selecting A3 as the output size?
Lots of reasons really. We might want to crop, straighten, sharpen...all these things need to be done. It's much better to make the print ready in Photoshop, which will do the best job without loss of quality.But when you set the image to print at, say A3, the printer will map the image to fit it to that paper size (unless you print at 100%). We've established that a K5 image has enough pixels to provide the printer with about 300PPI at A3 so why not simply send it to print, selecting A3 as the output size?
I print whatever size and shape I need within the bounds of an A3 piece of paper. Any trimming is done afterwards, as necessary.
Best regards, John
Posted 23/07/2012 - 21:48
Link
DoctorJeff wrote:
Now, to me, that is not exactly what you would call "bugger all difference". Resizing was done in PS Elements 10. No other PP was applied. And yes, I have the original DNG file as well (I always shoot RAW + JPEG).
Geoff
Geoff, what I think you have done is resample the image. You have changed the number of pixels. Is it really still 1400x1050 pixels? I'm going to go out on a limb and say your resized image was 336 pixels long. Do you think you could check that?Now, to me, that is not exactly what you would call "bugger all difference". Resizing was done in PS Elements 10. No other PP was applied. And yes, I have the original DNG file as well (I always shoot RAW + JPEG).
Geoff
I have just done my own test:
The 72PPI image, and the 300PPI image have the same number of pixels (1400 x 1050), and were both 1.9MB when saved as max. quality jpegs.
Posted 23/07/2012 - 21:52
Link
johnriley wrote:
Lots of reasons really. We might want to crop, straighten, sharpen...all these things need to be done. It's much better to make the print ready in Photoshop, which will do the best job without loss of quality.
This does make some sense, as you can view your image at the real 'print size' on the computer screen, so you may get a better idea of how your changes are going to impact the print. It doesn't really matter what size the image is for cropping or straightening though.
Lots of reasons really. We might want to crop, straighten, sharpen...all these things need to be done. It's much better to make the print ready in Photoshop, which will do the best job without loss of quality.
Posted 23/07/2012 - 21:54
Link
As an aside, and this is an excellent learning process, the actual competition rules ask for 1400x1050 pixels exactly. I take your point about the ppi being irrelevant, but in the absence of wanting to get a real migraine I have always used 72ppi anyway. Why struggle when it's so easy to do it that way?
Where the image shape is not suitable for 1400x1050, it needs placing on a 1400x1050 black canvas. This means vertical shots are relatively small, which unfortunately can reduce their impact.
Where the image shape is not suitable for 1400x1050, it needs placing on a 1400x1050 black canvas. This means vertical shots are relatively small, which unfortunately can reduce their impact.
Best regards, John
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8880 posts
16 years
Lancashire
It's a right mess more like crazy paving than dots
Pentax K-1 + K-5 and some other stuff
Algi