Against the grain... Again. DPI PPI SPI matter, even if you do not like it
Sep 18, 2017 06:01:42 #
The importance of the D/P/S-PI matter. Many here and elsewhere consider it a myth but if the same folks would even consider taking the time to think they may remember some of the following...
The D, P ans S represent a pixel. That alone should kill the 'myth' argument.
A pixel is the lowest form of a digital image regardless of media used to create, modify or see it.
The smallest pixel in a display is on the screen of some smart phones and the largest on large screen TVs.
The size influences the light quality and the resolution.
72DPI
Many folks are at war with the 72DPI... Where do you find it? Who use that crappy older standard? Well, every WEB site that converts or resize an image to display it on their page (like UHH - not to name one) use JPG 72DPI. Just saying. Problem? The larger the image you upload and then reduced byt the host server the softer it appears, simple at that. Create an image that corresponds to UHH display size (600x800) with 72 DPI and it will be sharp. I have posted two images for comparison long (few months) ago.
Display
If you have the right drivers for your OS and display you should have no issue unless you use a ruler to check for printing size. Note that many imaging software ask for your screen native DPI. Ever wonder why? Simply because more often than not high pixel displays use virtual resolution. But then again this also a myth.
Printing
Interestingly enough, many of those high end camera produce so-so prints when other using less capable produce incredible prints... Ever wondered why?
Here again very few use the tools at their disposal to print correctly. To have the optimal printing rendition you must set your image to the ratio you want then set the DPI then resize the image in inches (or centimeters) it will be printed at and then make corrections due to the re-sampling modification. Once again this is not a joke for any serious photographer who prints. For the other it is a myth. In short, the larger the image the more prone to errors when resized by the printer - EVEN if you use a calibrated monitor and an ICC that is for the printer and the paper selected.
Camera
The larger the pixel the better the light quality but the lower the resolution. One can successfully argue* the light quality is not all that much even if in a lab it is. High end cameras like the Canon 50mb, the current D810 offer the smallest pixel in the DSLR market but....
A smaller pixel means it is more prone to record minute motion than a larger pixel. Here again the pixel is important in more ways than one.
Then you have the use of the image... High pixel does not mean 'crop' to correct poor skills or poor choice of lens. It means you can print larger (MUCH larger) and better prepare for the end product.
So... DPI, PPI, SCI and whatever per inch just does not count for anything. I read it some where, it is true, it simplifies everything. Only stupid peoples who think they are photographers use this old legend.
-----
* Health, taste and environment when viewing are constant factors.
The D, P ans S represent a pixel. That alone should kill the 'myth' argument.
A pixel is the lowest form of a digital image regardless of media used to create, modify or see it.
The smallest pixel in a display is on the screen of some smart phones and the largest on large screen TVs.
The size influences the light quality and the resolution.
72DPI
Many folks are at war with the 72DPI... Where do you find it? Who use that crappy older standard? Well, every WEB site that converts or resize an image to display it on their page (like UHH - not to name one) use JPG 72DPI. Just saying. Problem? The larger the image you upload and then reduced byt the host server the softer it appears, simple at that. Create an image that corresponds to UHH display size (600x800) with 72 DPI and it will be sharp. I have posted two images for comparison long (few months) ago.
Display
If you have the right drivers for your OS and display you should have no issue unless you use a ruler to check for printing size. Note that many imaging software ask for your screen native DPI. Ever wonder why? Simply because more often than not high pixel displays use virtual resolution. But then again this also a myth.
Printing
Interestingly enough, many of those high end camera produce so-so prints when other using less capable produce incredible prints... Ever wondered why?
Here again very few use the tools at their disposal to print correctly. To have the optimal printing rendition you must set your image to the ratio you want then set the DPI then resize the image in inches (or centimeters) it will be printed at and then make corrections due to the re-sampling modification. Once again this is not a joke for any serious photographer who prints. For the other it is a myth. In short, the larger the image the more prone to errors when resized by the printer - EVEN if you use a calibrated monitor and an ICC that is for the printer and the paper selected.
Camera
The larger the pixel the better the light quality but the lower the resolution. One can successfully argue* the light quality is not all that much even if in a lab it is. High end cameras like the Canon 50mb, the current D810 offer the smallest pixel in the DSLR market but....
A smaller pixel means it is more prone to record minute motion than a larger pixel. Here again the pixel is important in more ways than one.
Then you have the use of the image... High pixel does not mean 'crop' to correct poor skills or poor choice of lens. It means you can print larger (MUCH larger) and better prepare for the end product.
So... DPI, PPI, SCI and whatever per inch just does not count for anything. I read it some where, it is true, it simplifies everything. Only stupid peoples who think they are photographers use this old legend.
-----
* Health, taste and environment when viewing are constant factors.
Sep 18, 2017 07:50:57 #
Interesting....I am a rank beginner & know very little about the finer details of digital photography. This helps. I still do not know enough to contribute anything meaningful to the conversation but this helps me a lot in my research & readings about the subject. I will be reading new info with a better understanding of these little guys called pixels & dots . Way to soon to agree or disagree on the subject. Thank you...Walt
Sep 18, 2017 09:26:43 #
Since I my Photographic Art, I have a significant need for what's on the screen matching what gets printed. When I bought a 4K monitor, I had great difficulty doing that. Taking a ruler to the screen showed that what was on the screen was not the same size as what was going to be printed. Finally I found how to set the screen resolution in Photoshop - Edit, Preference, Units & Rulers, Screen Resolution. In order to get a 1:1 ratio, I had to set my screen resolution to 163 pixels per inch with a print resolution (for Fine Art America) of 100 pixels per inch. Yes, pixels matter.
Sep 18, 2017 14:07:33 #
[quote]... Well, every WEB site that converts or resize an image to display it on their page (like UHH - not to name one) use JPG 72DPI... [quote\]
No. All Web sites don't use DPI (and especially 72 DPI) because it is meaningless - they use pixels (Ypixels x Xpixels). Why is it meaningless? Because (a) DPI is a physical dimension referring to dots on a print (a printing term) and has nothing to do with pixels, which are a numeric RGB value that are displayed on a monitor, and (b) all displays for web pictures are not the same size, so any DPI measurement would vary depending on the display. Notice that you mentioned that the display size for UHH photos is 800 x 600 PIXELS. If DPI were to equal PPI and 72 DPI was the "standard" (they aren't and it isn't) then that would imply an image of ~ 11"x8.5", which is not the size I'm displaying on my IPad, IPhone or 24" monitor. See how ridiculous this DPI measurement is when applied to electronic displays? Different web sites have different "standard" dimensions for photos, but it is expressed in Pixels, not DPI.
DPI IS a useful printing term. It originated from the definition of the Pica where 12 points=1/6", thus 1"=72 points. It was adopted by Apple in the 90s such that their Applewriter printer was 72 DPI, which matched their display. It is also shown as the default X and Y values in EXIF data, but it has zero relevance to electronic images which are measured in pixels unless we are discussing printing.
No. All Web sites don't use DPI (and especially 72 DPI) because it is meaningless - they use pixels (Ypixels x Xpixels). Why is it meaningless? Because (a) DPI is a physical dimension referring to dots on a print (a printing term) and has nothing to do with pixels, which are a numeric RGB value that are displayed on a monitor, and (b) all displays for web pictures are not the same size, so any DPI measurement would vary depending on the display. Notice that you mentioned that the display size for UHH photos is 800 x 600 PIXELS. If DPI were to equal PPI and 72 DPI was the "standard" (they aren't and it isn't) then that would imply an image of ~ 11"x8.5", which is not the size I'm displaying on my IPad, IPhone or 24" monitor. See how ridiculous this DPI measurement is when applied to electronic displays? Different web sites have different "standard" dimensions for photos, but it is expressed in Pixels, not DPI.
DPI IS a useful printing term. It originated from the definition of the Pica where 12 points=1/6", thus 1"=72 points. It was adopted by Apple in the 90s such that their Applewriter printer was 72 DPI, which matched their display. It is also shown as the default X and Y values in EXIF data, but it has zero relevance to electronic images which are measured in pixels unless we are discussing printing.
Sep 18, 2017 16:27:02 #
No. All Web sites don't use DPI (and especially 72 DPI) because it is meaningless - they use pixels (Ypixels x Xpixels). Why is it meaningless? Because (a) DPI is a physical dimension referring to dots on a print (a printing term) and has nothing to do with pixels, which are a numeric RGB value that are displayed on a monitor, and (b) all displays for web pictures are not the same size, so any DPI measurement would vary depending on the display. Notice that you mentioned that the display size for UHH photos is 800 x 600 PIXELS. If DPI were to equal PPI and 72 DPI was the "standard" (they aren't and it isn't) then that would imply an image of ~ 11"x8.5", which is not the size I'm displaying on my IPad, IPhone or 24" monitor. See how ridiculous this DPI measurement is when applied to electronic displays? Different web sites have different "standard" dimensions for photos, but it is expressed in Pixels, not DPI.
DPI IS a useful printing term. It originated from the definition of the Pica where 12 points=1/6", thus 1"=72 points. It was adopted by Apple in the 90s such that their Applewriter printer was 72 DPI, which matched their display. It is also shown as the default X and Y values in EXIF data, but it has zero relevance to electronic images which are measured in pixels unless we are discussing printing.[/quote]
Type all you want. Do a simple test. Upload a large image whatever size or DPI. It will be less than sharp, regardless of site. You know that.
Now pre reduce this image to the required size with the DPI the site uses. Sharpen for new size and see the difference.
D = dot = pixel regardless of what ever you want to call it or finagle about.
As long as someone promotes DPI/PPI/SPI (x)PI as myths there will be seriously disappointed folks when they look at their prints. Yes 72DPI is an old standard that was created at the same time as the JPG format and adopted as a WEB standard. Yes it needs updating. A display uses the pixel number but when the software re-sample the file to adjust it it uses the accursed 72 DPI or whatever the programmer decides (easier to use the default - even old). No, 72 DPI is not dead or even near dying, far from it as we see this standard all over. As to apple their top of the line was a 144 PPI with the matching 144 DPI screen.
As photographers we should pay attention instead of dismissing this as 'myth' and clamor up and down that DPI PPI or SPI does not matter. It does, it did before and will still matter in the future unless we have a complete change of technology.
You try to compare display and print and sensor (x)PI when there is absolutely no comparison other than the (x) something you
d a large image whatever size or DPI. It will be less than sharp. You know that.
Now pre reduce this image to the required size with the DPI the site uses. Sharpen for new size and see the difference.
D = dot = pixel regardless of what ever you want to call it or finagle about.
As long as someone promotes DPI/PPI/SPI as myths there will be seriously disappointed folks when they look at their prints. Yes 72DPI is an old standard that was created at the same time as the JPG format and adopted as a WEB standard. Yes it needs updating. A display uses the pixel number but when the software re-sample the file to adjust it it uses the accursed 72 DPI or whatever the programmer decides (easier to use the default - even old). No, 72 DPI is not dead or even near dying, far from it as we see this standard all over. As to apple their top of the line was a 144 PPI with the matching 144 DPI screen.
As photographers we should pay attention instead of dismissing this as 'myth' and clamor up and down that DPI PPI or SPI does not matter. It does, it did before and will still matter in the future unless we have a complete change of technology.
You try to compare display, print and sensor (x)PI when there is absolutely no comparison other than the (x), something you selectively ignore. EACH has a different purpose.
DPI IS a useful printing term. It originated from the definition of the Pica where 12 points=1/6", thus 1"=72 points. It was adopted by Apple in the 90s such that their Applewriter printer was 72 DPI, which matched their display. It is also shown as the default X and Y values in EXIF data, but it has zero relevance to electronic images which are measured in pixels unless we are discussing printing.[/quote]
Type all you want. Do a simple test. Upload a large image whatever size or DPI. It will be less than sharp, regardless of site. You know that.
Now pre reduce this image to the required size with the DPI the site uses. Sharpen for new size and see the difference.
D = dot = pixel regardless of what ever you want to call it or finagle about.
As long as someone promotes DPI/PPI/SPI (x)PI as myths there will be seriously disappointed folks when they look at their prints. Yes 72DPI is an old standard that was created at the same time as the JPG format and adopted as a WEB standard. Yes it needs updating. A display uses the pixel number but when the software re-sample the file to adjust it it uses the accursed 72 DPI or whatever the programmer decides (easier to use the default - even old). No, 72 DPI is not dead or even near dying, far from it as we see this standard all over. As to apple their top of the line was a 144 PPI with the matching 144 DPI screen.
As photographers we should pay attention instead of dismissing this as 'myth' and clamor up and down that DPI PPI or SPI does not matter. It does, it did before and will still matter in the future unless we have a complete change of technology.
You try to compare display and print and sensor (x)PI when there is absolutely no comparison other than the (x) something you
d a large image whatever size or DPI. It will be less than sharp. You know that.
Now pre reduce this image to the required size with the DPI the site uses. Sharpen for new size and see the difference.
D = dot = pixel regardless of what ever you want to call it or finagle about.
As long as someone promotes DPI/PPI/SPI as myths there will be seriously disappointed folks when they look at their prints. Yes 72DPI is an old standard that was created at the same time as the JPG format and adopted as a WEB standard. Yes it needs updating. A display uses the pixel number but when the software re-sample the file to adjust it it uses the accursed 72 DPI or whatever the programmer decides (easier to use the default - even old). No, 72 DPI is not dead or even near dying, far from it as we see this standard all over. As to apple their top of the line was a 144 PPI with the matching 144 DPI screen.
As photographers we should pay attention instead of dismissing this as 'myth' and clamor up and down that DPI PPI or SPI does not matter. It does, it did before and will still matter in the future unless we have a complete change of technology.
You try to compare display, print and sensor (x)PI when there is absolutely no comparison other than the (x), something you selectively ignore. EACH has a different purpose.
Sep 18, 2017 17:03:43 #
Ron, I've read your initial post and response several times and I'm a bit confused, but maybe I'm just not understanding your point(s). To sum up, I DON't think DPI or PPI is a myth at all. I think:
- DPI is a useful printing term to define print resolution.
- I don't think DPI=PPI although the terms are often used (incorrectly) interchangeably. Conversely, I don't think DPI is
the correct way to describe an electronic/computer display image composed of pixels.
- I don't think 72 DPI is any sort of web standard
- I think web imagery is correctly described in pixels (Y x X)
- I do think PPI can be used to describe display resolution
Perhaps we actually agree to some extent.
Regards,
Chris
- DPI is a useful printing term to define print resolution.
- I don't think DPI=PPI although the terms are often used (incorrectly) interchangeably. Conversely, I don't think DPI is
the correct way to describe an electronic/computer display image composed of pixels.
- I don't think 72 DPI is any sort of web standard
- I think web imagery is correctly described in pixels (Y x X)
- I do think PPI can be used to describe display resolution
Perhaps we actually agree to some extent.
Regards,
Chris
Sep 18, 2017 19:07:11 #
Chris, I am trying to tell folks that (x)PI is used all over the place from capturing to printing to viewing. (x)PI has a physical size used in calculation when resizing. If you downsize you have a softness. If you upside you have pixelization.
Anyone who understand pixels does not define it by how many there is per inch, but by its size. The media (x)PI determines the resolution - any media-. However you look at it when resizing the software (screen driver, printer or camera hard coding) takes that (x)PI value into consideration. If not it would not make any sense to have a (x)PI at all.
Knowing this, for best result when printing (especially) one has to resize using first the (x)PI then the print size. Hopefully the print ratio has been set before anything else. The re-sampling that takes place creates a softness that must be corrected when printing. It is also possible that the light IQ changes too, depending in the subject complexity.
When I send anything to a printer I set the ratio then (P)PI - per the printer instruction - then resize to finally correct softness issues. Note: I always downsize an image.
Anyone who understand pixels does not define it by how many there is per inch, but by its size. The media (x)PI determines the resolution - any media-. However you look at it when resizing the software (screen driver, printer or camera hard coding) takes that (x)PI value into consideration. If not it would not make any sense to have a (x)PI at all.
Knowing this, for best result when printing (especially) one has to resize using first the (x)PI then the print size. Hopefully the print ratio has been set before anything else. The re-sampling that takes place creates a softness that must be corrected when printing. It is also possible that the light IQ changes too, depending in the subject complexity.
When I send anything to a printer I set the ratio then (P)PI - per the printer instruction - then resize to finally correct softness issues. Note: I always downsize an image.
Sep 18, 2017 19:39:03 #
Rongnongno wrote:
Chris, I am trying to tell folks that (x)PI is use... (show quote)
👍👍 Now I am with you Ron.
Sep 19, 2017 07:06:25 #
Ron, I have the feeling that you are saying something important here, but I am really having a tough time following you. Could be the hour. Could be all the symbology. Could be that I'm seeing double from all the places where you repeat yourself. I'd really like to understand. Could you "tighten that baby up a bit" and make your point more succinctly?
Sep 19, 2017 07:16:21 #
DPI is dots per inch used in offset printing and was adopted with the Advent of non-darkroom photo printing. PPI is the measure of pixels per inch in an electronic image. Enlarge both and you will see the difference. The 72 measure comes into play because most computer monitors display at 72 pixels per inch.
Sep 19, 2017 08:09:52 #
Hmmm I think you are putting two things together that don't belong really. A website is usually going to scale an image to a fixed width height or a percentage width height. Some sites are a little more sophisticated, smugmug for example gets the viewport size (the size of the browser window) in pixels in order to select which image size will be served to your client. E.g a 4k screen will get a larger image file than a 1080p sized screen.
Unfortunately there is no provision to upload your image pre sized at half a dozen sizes. UHH for example doesn't get you to upload 2 images one for screen display and another for download. The server resizes using what ever method its been programmed to use. Often a graphics program will give a number of options for resizing routines and presumably there is a difference in the result.
So yes you can sharpen better for a given size, in practice you usually can't.
If you have an Epson Printer you can use a handy trick to print black & white using just black ink you size your image to 360 dpi and tell it to print grayscale on plain paper (photo paper it mixes inks badly) what it does is dither. It's actually got 1440 dpi capability and because each pixel is an exact fraction of the 1440 it does a very good job of putting down black dots more where its darker and less where its lighter giving a very good illusion of printing in gray our eyes don't resolve the dots so we interpret the densities as shades of gray.
If you are using a canon printer 300 dpi is ideal for the printer and it's arguably going to look that bit better if your 8 by 10 photo is resized to 3000 by 2400 pixels and sharpened at that size. Even side by side I don't think you will notice the difference.
Unfortunately there is no provision to upload your image pre sized at half a dozen sizes. UHH for example doesn't get you to upload 2 images one for screen display and another for download. The server resizes using what ever method its been programmed to use. Often a graphics program will give a number of options for resizing routines and presumably there is a difference in the result.
So yes you can sharpen better for a given size, in practice you usually can't.
If you have an Epson Printer you can use a handy trick to print black & white using just black ink you size your image to 360 dpi and tell it to print grayscale on plain paper (photo paper it mixes inks badly) what it does is dither. It's actually got 1440 dpi capability and because each pixel is an exact fraction of the 1440 it does a very good job of putting down black dots more where its darker and less where its lighter giving a very good illusion of printing in gray our eyes don't resolve the dots so we interpret the densities as shades of gray.
If you are using a canon printer 300 dpi is ideal for the printer and it's arguably going to look that bit better if your 8 by 10 photo is resized to 3000 by 2400 pixels and sharpened at that size. Even side by side I don't think you will notice the difference.
Sep 19, 2017 08:20:05 #
Larz wrote:
DPI is dots per inch used in offset printing and was adopted with the Advent of non-darkroom photo printing. PPI is the measure of pixels per inch in an electronic image. Enlarge both and you will see the difference. The 72 measure comes into play because most computer monitors display at 72 pixels per inch.
The PPI of a monitor can be anything e.g a 55 inch hd screen in 1080p is 1080 pixels high by 1920 wide. (approximately) but so can be a 19inch screen. the 19" and the 55" have the same number of pixels but cannot have the same dpi. There isn't a universal screen size and there isn't a universal dpi. 72dpi was only a convenient hack when computers and printers were far more primitive than they are today.
Sep 19, 2017 08:51:09 #
Rongnongno wrote:
The importance of the D/P/S-PI matter. Many here ... (show quote)
I mostly agree with everything you've written, but on the topic of pixel count, it's not about making large prints. Billboards have been made from 8 mp images, or 3264x2448 px. I'm sure you've seen the Apple billboards advertising the image quality of their iPhone 6. In similar fashion, graphic wraps for semi-trucks have been made from medium resolution digital cameras.
http://lifeinlofi.com/more/iphone-photo-sizes-2007-2013/
Museums and galleries routinely display giant prints - 40x60 and larger - made from 6-18 mp cameras.
The whole thing has to do with the eye's ability to perceive fine detail and image flaws. If you were to look at a newspaper's fine print, and assuming you have perfect vision, you'd have no problem reading it at 12-15 in away. But paste that newspaper on the wall and move away, to say 10 feet, and you wouldn't be able to read anything but the headlines. Pictures printed in newspapers look pretty low quality due to the 85 LPI (lines per inch) halftone screen. Again, up close images look pretty bad, but when you move away, your eyes can no longer see the dots, and the images appear much smoother.
So, high MP cameras are not about making giant prints, as much as they are about cropping. And cropping is something that can be used to focus the eye on an element in the picture, or remove extraneous elements that do not contribute to the main focus, and in the case of wildlife and sports, to create emphasis. Ideally I would love to shoot my birds in flight with a 1200mm or longer lens and not have to crop (much), but the mechanics and logistics of using a lens that large (it would have to be fast to be able to use faster shutter speeds and reasonable ISOs, it would most certainly be tripod mounted, and it would be next to impossible to track something moving in the viewfinder.
I often down-sample an image in order to average the noise in adjacent pixels, resulting in less overall noise and slight improvement in image detail. DXO Labs has written on the subject of down sampling and after reading their position it makes a lot of sense.
On the other hand, when I do landscape, I rarely crop provided I can position myself exactly where I want to be and there are no obstructions in the way or distracting elements in the scene. I do find I crop more with a prime lens than a zoom. Sometimes you just can't get into the perfect position, like when I am hanging off wet slippery rocks trying to get a good shot of a waterfall, or hiding behind a tree trying to get a shot of a black bear without becoming bear chow.
If I use a very wide angle lens I will crop the edges to minimize the volume distortion that can be ugly a the sides and corners. Also, if I end up tilting the camera upwards, cropping is necessary when you perform the correction for converging verticals.
Sometimes when I shoot macro I am really close to the ground, and it is not always practical to lie in the mud on my belly to get a great composition. So I back off a bit, shoot a wider view, and crop later.
I just wanted to lend some clarity to the notion that cropping is to make up for wrong lens and shooting distance choices, which it most certainly does, but there are other perfectly valid reasons to crop.
Most small cameras have pixel sizes that are far below those found in the D810, 5DS and others.
Here is a list of some popular cameras and pixel sizes ranging from high quality point and shoot to high mp full frame cameras:
Nikon D810 - 23.72 µm²
Canon 5DS - 17.06 µm²
D7200 - 15.13 µm²
Canon 80D - 13.91 µm²
Olympus OM-D E-M1 Mark II - 11.02 µm²
Sony RX 10 III - 5.76 µm²
Canon G 16 - 3.50 µm²
You can find a pretty exhaustive list at:
https://www.digicamdb.com/specs/canon_eos-80d/
Sep 19, 2017 08:52:47 #
I don't disagree with your math. My only point was nomenclature. Do not electronic devices display in pixels and not dots?
Sep 19, 2017 11:10:17 #
Larz wrote:
...The 72 measure comes into play because most computer monitors display at 72 pixels per inch.
No they aren't (that really is a myth). Measure your monitor(s) and divide the dimension in inches into the resolution to convince yourself otherwise. As examples, one of my Dell monitors measures 20-1/4 x 10-1/2 and the current resolution is 1280x1024. My IPad is 7-3/4 x 5-3/4 and is 1024x768. Obviously, it depends on the resolution you set, but you'll be hard pressed to find a monitor and resolution combination that is 72 PPI, and even if you do, it certainly won't apply to "most" monitors.
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