# Typical Output settings of images from lightroom



## VPick (May 23, 2012)

Ok I am new to this forum.  I have been using lightroom for sometime but have never figured out the best export settings for image quality and smallest file size. For printing, viewing on internet, viewing on computer, viewing with projector, viewing on hd tv

Specifically:  I want to know what the best output settings ( both in total file size, and dimensions pixel by pixel and inches by inches, dpi etc. (are for 1. *printing* images 2. *posting* images on the internet assuming the viewer has *large* screens 3. *posting* images on the internet assuming the viewer has *small* screen 4. viewing images from burned disk on *computer and projector *5. Viewing images on *HD TV
*
I would like specific recommendations for each and why this is recommended i.e. the internet will not display any high resolution than ....

I realize this maybe a lot but seems like all the same type of discussion.

Thanks for any help,


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## Mark Sirota (May 23, 2012)

Welcome to Lightroom Forums.

You're looking for "best", but for the most part there isn't such a thing, just tradeoffs.

For printing: You need to know the ideal output resolution of the printer. If it's 300 pixels per inch, and you're printing an 8x10 inch print, then you want 2400x3000 pixels.

For posting on the internet, it depends on how big the screens are, what hosting service, your tolerance for upload and download speeds, and how much risk you're willing to take about large image files getting stolen. And also whether you want people to be able to "zoom in".

For showing on a computer, projector, or TV, size for the resolution of the screen.  For HDTV that's normally 1920x1080, for computers and projectors it varies greatly.


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## VPick (May 23, 2012)

I knew it would not be a simple answer.
Perhaps you can help me with some clarification on my part.  Looking for output settings for:

*1. **printing images say I want to print 3 sizes 8X10, 11X14 and 11X17, 
Goal Best Resolution the printer can handle to get best image quality,  (seems most printers or 300dpi is that correct?)

What would be the best output settings and way to specify for each?  
What is the best way to specify each in LR export communication window?
**-----------------------------------------------------------------------------------------------------------------------------------------------
I have been told that the internet will only display 72 dpi max regardless of higher file settings
Goal:  Best image quality but smallest file preferably one that will not have file suitable for printing.

2. posting images on the internet assuming the viewer has large screens assume screen size of 21 to 25 inch diagonal
**
What would be the best output settings and way to specify for each?  
**What is the best way to specify each in LR publish communication window?**
**
3. posting images on the internet assuming the viewer has a small screen I phone?
**
What would be the best output settings and way to specify for each?  
**What is the best way to specify each in LR publish communication window?**
**-----------------------------------------------------------------------------------------------------------------------------------------------
**
4. viewing images from burned disk on computer and projector **assume screen size of 21 to 25 inch diagonal display
assume projector will make it very large (does that matter when using a projector?)
Goal:  Good viewing image quality

What would be the best output settings and way to specify for each?
**What is the best way to specify each in LR output communication window?**


**-----------------------------------------------------------------------------------------------------------------------------------------------**5. Viewing images on HD TV 1080P from burned cd and or dvd
I have had my HD TV blue ray combination say that there is too many pixels to display image
**
Goal:  Good image viewing quality

What would be the best output settings and way to specify for each?
**What is the best way to specify each in LR output communication window?**

*


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## VPick (May 23, 2012)

I knew it would not be a simple answer.
Perhaps you can help me with some clarification on my part. Looking for output settings for:

*1. **printing images say I want to print 3 sizes 8X10, 11X14 and 11X17, 
Goal Best Resolution the printer can handle to get best image quality, (seems most printers or 300dpi is that correct?)

What would be the best output settings and way to specify for each? 
What is the best way to specify each in LR export communication window?
**-----------------------------------------------------------------------------------------------------------------------------------------------
I have been told that the internet will only display 72 dpi max regardless of higher file settings
Goal: Best image quality but smallest file preferably one that will not have file suitable for printing.

2. posting images on the internet assuming the viewer has large screens assume screen size of 21 to 25 inch diagonal
**
What would be the best output settings and way to specify for each? 
**What is the best way to specify each in LR publish communication window?**
**
3. posting images on the internet assuming the viewer has a small screen I phone?
**
What would be the best output settings and way to specify for each? 
**What is the best way to specify each in LR publish communication window?**
**-----------------------------------------------------------------------------------------------------------------------------------------------
**
4. viewing images from burned disk on computer and projector **assume screen size of 21 to 25 inch diagonal display
assume projector will make it very large (does that matter when using a projector?)
Goal: Good viewing image quality

What would be the best output settings and way to specify for each?
**What is the best way to specify each in LR output communication window?**


**-----------------------------------------------------------------------------------------------------------------------------------------------**5. Viewing images on HD TV 1080P from burned cd and or dvd
I have had my HD TV blue ray combination say that there is too many pixels to display image
**
Goal: Good image viewing quality

What would be the best output settings and way to specify for each?
**What is the best way to specify each in LR output communication window?**
*


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## Mark Sirota (May 24, 2012)

VPick said:


> printing images say I want to print 3 sizes 8X10, 11X14 and 11X17,
> Goal Best Resolution the printer can handle to get best image quality, (seems most printers or 300dpi is that correct?)



Many are 300.  Some are 360, some are 240...  Check your printer specifications, or if you're using a lab, ask them.  Is this the same file that's going to be printed at three different sizes and aspect ratios, or are you creating a file for each size and shape?



> I have been told that the internet will only display 72 dpi max regardless of higher file settings



Simply false.  PPI (not DPI) is irrelevant on the web.  All that matters is the pixel dimensions.  Most monitors these days are somewhere around 96-150 PPI, though Apple "Retina Displays" are far more dense.



> Goal: Best image quality but smallest file preferably one that will not have file suitable for printing.



Depends on your tolerance for quality.  Some people make 4x6 inch prints from 400x600 pixel images and are happy with them, at only 100 PPI.



> 2. posting images on the internet assuming the viewer has large screens assume screen size of 21 to 25 inch diagonal



Also depends on the software they're using, and how much space is taken up on the screen by other things.  Flickr and Facebook now display images up to 2048 pixels wide, though the default is much smaller.  Where will these images be hosted, and what do those pages look like?



> 3. posting images on the internet assuming the viewer has a small screen I phone?



The iPhone 4/4S has a resolution of 960x480 pixels (326 PPI). The latest iPad is 2048x1536, which is more than an HDTV.

So those dimensions would fill the screen on those devices, but would not allow the user to zoom in.  Other smartphones and tablets will have different resolutions.



> 4. viewing images from burned disk on computer and projector [/B]*assume screen size of 21 to 25 inch diagonal display*


*

Again, check the dimensions for your display.  Ideally, you'd size it to exactly those dimensions so that the device (or host computer) doesn't have to resize for you, which will reduce quality.




			5. Viewing images on HD TV 1080P from burned cd and or dvd
		
Click to expand...


The source doesn't matter, this is (finally!) an easy one.  1920x1080.

I recognize that you're looking for a simple formula, but there just isn't one. You have to do a little legwork and figure it out for your intended audience.*


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## erro (May 24, 2012)

I have an article (in swedish) regarding image size, resolution, PPI/DPI:
http://erro.se/artiklar/Bildstorlek

I'm also working on an english translation, so here it comes. Warning: much text....

Few things are subject to such confusion and discussion as image size,  resolution, PPI and DPI. Especially PPI and DPI. And the funny thing is  that you don't really have to care about it at all, at least when it  comes to the needs of the every-day hobby photographer. And everything  boils down to "size", and the fact that the size of a photo shown on a  computer screen is something completely different than the size of a  photo printed on paper.

*The short and simple explanation*



PPI  and DPI has no relevance whatsoever as long as we are displaying an  image on a computer screen. An image consists of pixels, a screen  displays pixels, so it's all a matter of pixels.
If we (or a lab) print the image, PPI and DPI _may_ matter. Note the word "may". PPI and DPI doesn't have to matter. You can ignore it too.
You can print at any size (but whether it will look good or not depends on several factors)
When  you display images on the web you have no control (and you can't  guarantee that someone else sees the images the same way you do)
*The long explanation*
So you want the long explanation? OK, read on...
Let's start by establishing a few facts:


An image can have any size
An image doesn't have just one size, but many, depending on how you view the concept of "size"
Any image can be printed at any size
Any image can be displayed at any size
"Good quality" is a relative and personal concept, which is also dependent on many different factors
If  someone asks you what size a certain image is, what do you answer? Is  it a physical size in inches? Or is it the total number of pixels? Or  the number of pixels along the sides? Or how much disk space it takes on  the hard drive?
And where do the terms PPI and DPI enter the game? And do you really need to bother?
*Disk space*
Let's  start with the simplest version of size, and the one you probably less  often mean by "size": the amount of space an image occupies on the hard  disk (or some other storage media). How many megabytes or kilobytes is  it? This size varies depending on a lot of factors: the number of  pixels, compression, color depth, file format etc. But what doesn't  affect the file size is this cryptic PPI/DPI, which we'll come to later.
Different PPI but the same number of pixels (3872*2592) and same file size (2850 kB)
The  size of an image file depends on many things: As an example I've used  an image with 3872*2592 pixels. That is roughly 10 million pixels, or  more precisely 10036224 pixels. Each pixels consists of three colors:  red, green and blue. In an ordinary image with 8 bit color depth, each  of these colors can assume 256 different nuances from dark to bright.  With some binary math you realize that 256 levels equals 8 bits, i.e.  one byte. The "raw" image content is thus 10036224 pixels with three  colors per pixel and one byte lightness information per color.  10036224*3*1=30108672 bytes. Roughly 30 million bytes. Or in megabytes:  30108672/1024/1024=28,7 MB. (By "raw" image content I don't mean raw  file format, that is something else).
If we look at our images on  the computer they are normally not that big, and that is because images  are often compressed, e.g. with JPG. This compression (which in fact  also is a reduction, since image information that our eyes have a hard  time seeing is actually deleted) can be done in varying degree. High  compression gives you a small file size but also lower quality. Low  compression conversely gives larger file size but higher quality. But  even compression in the highest quality (the largest file size) give you  a file that is smaller than that of the raw image data. JPG is a  "destructive" image format, since it actually deletes information from  the image that can not be restored 100% correctly later. This is however  not a problem, as long as you don't delete too much, or re-save the  file too many times, since there is a certain "smartness" as to what is  deleted. Our eyes are also easily fooled to some degree, and besides we  have a brain that is very good at filling in the gaps. Of course, you  can save your images in non-destructive file formats, such as TIFF, but  then the files grow very large.

A JPG can be saved in 12 different quality levels, where 1 gives the most compression and 12 the least
*Size on screen and print*
Left  is then understanding the visual or physical size of an image. Partly  on screen and partly on print - because those are two different kind of  size. If we look at an image on a screen, the size is measured in pixels  and level of magnification. If we print the image, then we have a  physical size measured in centimeters or inches (or kilometers for that  matter).
To grasp the whole concept it helps understanding the  complete chain an image goes through, from the time of exposure until we  see it on screen or print.
The image is created in its original  format in the camera. Exactly how that is done is not of interest in  this discussion. The important thing is that some form of image is  created by the sensor in the camera, and thereby one property of the  image size is defined: the pixels. A sensor is built up by a number of  light sensitive areas (pixels) that we normally refer to by the  millions. A camera with a sensor that has ten million pixels is called  10 megapixel. Six millions is 6 megapixels, and so on.
This tells  us how many pixels the image has in total, but not how they are  distributed. Depending on what camera we use, there are sensors with  different proportions. A DSLR often have the classical slide film format  3:2, meaning the long edge is 50% longer than the short edge. A compact  camera often have a more square format, 4:3 where the long edge is 33%  longer than the short edge, the same proportions as an old CRT-tube TV.  Widescreen TV, as a comparison, has 16:9 proportions, with the long edge  being 78% longer than the short edge. anyway, knowing the total number  of pixels, and the proprtions of the sensor, we can calculate how long  the edges are in pixels. Or we can just look at the image information,  or read the camera manual.
Below are photos from four different cameras, with which I've taken similar photos of the same subject (as similar as possible):
Pentax K10D - DSLR with APS-C sized sensor
       10 megapixels
        3872*2592 pixels
        format 3:2
        sample image file size: 3,8 MB 

    KonicaMinolta Dimage A2 - advanced compact camera with sensor in 2/3"-size
        8 megapixels
        3264*2448 pixels
        format 4:3
        sample image file size: 3,6 MB 

    Canon IXUS 400 - normal compact camera with sensor in 1/1,8"-size
        4 megapixels
        2272*1704 pixels
        format 4:3
        sample image file size: 2,1 MB 

    Canon IXUS
        2 megapixels
        1600*1200 pixels
        format 4:3
        sample image file size: 0,6 MB 

Below are the four images resized to 600 pixels wide:

10 megapixels


8 megapixels


4 megapixels


2 megapixels

We  can take basically the same photo with all four cameras (same angle of  view and framing) but the four resulting image files will differ because  the sensors differ. Theoretically, all other things equal, a sensor  with more pixels will produce a more detailed photo since each pixel is  smaller. If you can actually see those details depends on what size you  view the image, ang how good the sensor is at actually capturing the  details. Another difference is the visual impression, where a physically  larger sensor (as in a DSLR) gives the ability to have a shallower  depth of field. This whole business of angle of views, framing, depth of  field, focal length och crop factors are subjects for a complete  article in itself.
*Viewing images on a screen*

Well,  once a photo is taken, the next step is usually to copy it to the  computer. Once in the computer you normally want to look at the image.  It can be done with the computers built-in image viewing program, or  some type of image editing program. Now we come to the next "size": what  size is the image on screen? And the question is also: what size is the  screen?


The image (and the sensor it came  from), and the screen are all built up using pixels, but with the  difference that a screen almost always have much fewer pixels than a  photo (or a sensor). As an example, a 17" or 19"-screen normally have  1280*1024 pixels which translates to 1,3 megapixels. A large 24" screen  has 1920*1200 pixels, equaling 2,2 megapixels. None of these screens can  display a photo from a 4 megpixel camera in its full native size, and  it gets even worse with cameras with higher resolution. To fit the whole  photo on screen it has to be resized.


If you  have ever used an image editing program you know that you can zoom the  images, often by applying a percentage value. 100% does not mean that  you view the whole photo, but rather that you view one pixel in the  photo as one pixel on the screen, meaning you see the photo in its  "native" size. And since the photo normally has much more pixels than  the screen, this equals to zooming in on the photo. In order to see the  whole photo we have to zoom out - how much depends on how many pixels  the photo is, and how many pixels the screen has. Zooming out so that  the entire photo fills the screen is often called "full screen" or  "custom size" or something. The program that is displaying the photo  will have to resize the photo to a proper size, which in some cases may  lead to reduced quality. This is because the photo has to be  recalculated, since many pixels in the photo have to be shown as one  pixel on the screen, since the photo is reduced. This is true for all  zoom levels other than 100%. Different programs have different methods  for doing this recalculation and the appearance of the photo can  therefore differ somewhat. It is however nothing I have personally  reacted to. Some ambitious photographers will resize their photos  themselves to the "correct" viewing size for their own screen, but I  regard that as an unnecessary step since I can't see the difference in  quality between the down-scaling done by me and that done automatically  by e.g. Windows built-in image viewer. If you on the other hand are  going to show photos on the web, then it makes sense to reduce them to  proper viewing size, partly for reducing the file size in kB/MB, partly  since web browser are much worse at resizing images. But, you'll see  that I have yet not mentioned size in centimeters or inches, or PPI or  DPI. That's because physical size is irrelevant when you are showing  photos on a screen, or on the web.


Screens come  in many different physical sizes (14", 17", 19", 24" ...) and  proportions (4:3, 5:4, 16:9, 16:10) and they can be used with many  different resolutions (800*600, 1024*768, 1280*1024, 1400*1050,  1600*1200, 1920*1200 ...). All this means that when you display a photo  on a screen there is really no way of knowing how large it will be  physically. You can of course measure it on your own screen, but if you  are showing photos on the web you have no control over what screens and  resolutions other people are using. And you can't demand that people use  a certain combination in order to see your photos. That's why the  photos size in pixels, along with perhaps a zoom level, is what  determins how a photo is displayed on screen. The strange PPI/DPI is of  no relevance since image pixels are shown with screen pixels.


PHOTO TO BE INSERTED: One and the same photo shown full screen on a few different screens

PHOTO TO BE INSERTED: One and the same photo shown at 100% on a few different screens

*PPI for screens*

Perhaps  you object now and say "screens actually have PPI 72, I've read that  somewhere!" True, I've read that too. It's an old truth that is no  longer true, but it has a hard time dying. It was true once upon a time  when computer graphics were in its beginning. If I remember correctly I  think it has something to do with the resolution 640*480 pixels on a 12"  screen, but I am not sure. Anyway, modern screens and resolutions today  gives higher PPI. Just do the math yourself. PPI=Pixels Per Inch.  Divide the resolution of the graphics card with the physical size of the  screen in inches (1 inch = 2,54 cm). If you don't want to measure  yourself I have some examples ready:


    14" laptop-screen (28,5*21,4 cm) and 1400*1050 pixels = 125 PPI
    19" flat screen (37,6*30,1 cm) and 1280*1024 pixels = 86 PPI
    24" wide flat screen (51,8*32,4 cm) and 1920*1200 pixels = 94 PPI
    37" widescreen-TV (82*46 cm) and 1366*768 pixels = 42 PPI

But  this PPI doesn't affect how the image is shown on screen. PPI is only  used when printing. If you want to. Displaying on screen is using pixels  and zoom levels.

A side-discussion here is the fact that the  four screens above not only have different PPI but also different  proportions. The 14" screen has 4:3, like an old TV or compact cameras.  The 19" screen has 5:4, a little more towards square. And the 24"  widescreen has 16:10 as opposed to 16:9 that we find in the widescreen  TV. Once again, a subject for a complete article in its own.


So,  do you actually see any difference between photos with different PPI on  screen? Below are three photos with the same size i pixels (600*400)  saved with three different PPI values. Do you see any difference? No, I  thought not.

...continued in next post...


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## erro (May 24, 2012)

...continued...

*Photos on the web*


When you want to show a photo on the web you basically have two options:


    Upload the photo in full size and let the web browser reduce it
    Reduce the photo yourself to proper viewing size and then show it as it is (100%)

The  second option is basically always the best. Sure, you can take a 10  megapixel photo and put it on your homepage. The downside is that it  will be very large measured in MB which means it will take a long time  do download, and space to store. If you then want to show it in say 640  pixels width, the web browser have to reduce its size which web browsers  doesn't always do very well. No, it's better to reduce the size  yourself to 640 pixels wide, look at it in 100% zoom and make sure it  looks OK. This photo will take less space and load faster. The web  browser can display the photo as it is, without resizing.


Original photo 3872*2593 pixels (2850 kB) which the web browser resize to 600 pixels wide


Photo resized to 600*402 pixels (147 kB) and shown just as it is

*Prints*

OK,  finally you may want to print the photo on a printer, or send it to a  lab for developing/enlargment/printing. And then you all of a sudden  have an output media with a specific physical size, e.g. 15*10 cm or  8*10 inches, or A4 or whatever. Now that strange PPI/DPI enters the  game. If you want to. You can also ignore it. You actually have a  choice.


No matter how you print the photo, its  pixels must somehow transform to physical dots of color on a piece of  paper. Depending on how large those pixels are printed, the final size  of the print will vary. Or the other way around: if you know the  physical size of the photo on paper, the size of the printed pixels will  vary.


When printing, you have three size-parameters to play with:
- the total number of pixels in the photo
- the physical paper size
- the size of the printed pixels


You  can vary one or two of those three in any way you want, and the  other(s) will adjust accordingly automatically (they will become what  they become). You can however not set specific values to all three in  any way you want, since they have a mutual relationship:

Resolution in PPI = Number of pixels divided by physical size

This means e.g. that:

    if you increase the physical size of the paper then you also have to increase the number of pixels, or decrease the PPI
    if you increase the PPI then you salso have to increase the number of pixels, or reduce the physical size
    if you supply a specific physical size and have a given number of pixels, then PPI will become whatever it becomes
    if you have a given number of pixels and supply a specific PPI, the physical size will become whatever it becomes
    and so on

The three basic formulas are:

    PPI = pixels / physical size
    pixels = PPI * physical size
    physical size = pixels / PPI

So, is it PPI or DPI we use?

    PPI=Pixels Per Inch, i.e. number of pixels per printed inch
    DPI=Dots Per Inch, i.e. number of printed dots per inch

What's  the difference? Well, the image is built up by pixels that we want to  print. The printer prints these pixels by using print dots. In order to  improve quality, and more importantly in order to be able to print  nuances that are mixes of the base colors, the printer uses many small  dots to print one pixel. So you use more dots than pixels. Higher DPI  than PPI. Getting complicated yet? But then again: most of the times you  can choose to ignore this.


Asume you have  photo from a 4 megapixel camera where the pixel dimensions are 2272*1704  pixels. You want to print this so that the long edge is 15 centimeters  (~6 inches). You have to spread those 2272 pixels across the 15 cm which  translates to ~151 pixels per centimeter. To get that in inches we  multiply by 2,54 which makes it ~385 pixels per inch, or PPI. So, on  every inch of that paper, the printer have to squeeze in 385 of the  image pixels. Each of these pixels have an RGB-value stating the exact  color (portions of red, green and blue).

The printer use a  different color model that instead of RGB is based on cyan, magenta,  yellow and black, called CMYK. The printer, or the printing program,  converts the pixels RGB-values to CMYK-values and in order to get  nuances and better quality each pixel is split up into smaller parts  that the printer prints as dots. Let's say each pixel is split into 9  smaller parts (3 in height and 3 in width), that means that each pixel  is printed with three times more dots along the height or width. DPI  (Dots Per Inch) is three times higher than PPI, or around 1154 DPI in  the example above. Unfortunately there is a lot of confusion around  these two abbreviations and they are often used alternately, which of  course doesn't make life easier for anyone.

But, as I wrote  before, you can choose to ignore this PPI/DPI business altogether. You  can let the programs and printers sort those things out by themself  automatically. What is actually interesting when printing is the two  factors that you control: the number of pixels in the image and the  physical size of the print. Remember what I wrote at the beginning: any  image can be printed at any size. If you have an image where the long  edge is 2272 pixels and tell the printer to print that as 15 cm, well  then PPI will become 385, as in the example above. If you want to print  that same image on an A4-paper where the long edge is 29,7 cm, well then  PPI will become (2272/29,7)*2,54=194. And if you want it one meter  wide, then PPI will become (2272/100)*2,54=58. The printer or the lab  will fix that for you, automatically.

*Print quality and sizes*


Will  the printed photos look good? Well, that's the next question, and here  PPI actually have some meaning. The lower the value the fewer pixels per  inch. Imagine an extreme case with PPI=1, meaning one pixel per inch.  Each pixel will be 2,54 cm high and wide. That's a pretty big blotch of  color. It will be hard to see any details in that photo if it is lying  on the table in front of you. But such a print doesn't lie on the table  in front of you, because the physical size of that print from a 4  megapixel camera would be 2272*1*2,54=5771 cm or 57,71 meters wide. Now  that's a print! Such a print is not viewed from one meter away, no you  are probably tens or hundreds of meter away from it. And then it  suddenly looks good. Resolution and "good quality" is also a matter of  vieweing distance and how large part of your field of vision is filled  with the image.


PHOTO TO BE INSERTED: Add some photos showing a billboard at distance and close-up

For  normal viewing of normal prints, say sizes up to perhaps A3-A4 (long  edge around 30-40 cm or 10-15 inches) that are viewed at arms length  there is a general recommendation of using 200-300 PPI. For larger  prints, that are generally viewed at greater distance, you can often  accept lower PPI. So you may wonder: why not always use 300 PPI to be on  the safe side, even if you are printing a huge poster? Well, the larger  physical print you want, while maintaining the same PPI, requires more  pixels (see the formulas above). When the photo is created it has a  certain number of pixels, and as long as they are enough you can use as  high PPI as possible. But if there are too few pixels, and you want to  use a higher PPI than those pixels can give you, then you have to create  those extra pixels in some way. This is called "interpolation" and can  be done by image editing programs or printers. And sure, as I said, any  photo can be printed at any size, or with any PPI, but when those new  pixels are created it means new image data is created that wasn't there  to start with. The new pixels are estimations, calculations and guesses  made by the program or the printer. The quality will never be better  than that of the original image. You can't create details in a photo  that weren't there from the beginning. You've probably seen movies where  the police can produce a tac sharp face from a muddy little photo. This  only works in the movies, not in the real world.

Depending on  what method is used for the interpolation you can get anything from bad  to good results. The worst method for photos is called "nearest  neighbor" where pixels are simply copied. The image is enlarged but it  gets very edgy and pixelated. For computer graphics and strict logotypes  it might work though. The best method is probably to use some sort of  dedicated interpolation program that has special algorithms for scaling  images up or down. A simpler, but often equally good method is to use  what is called "bicubic interpolation". This method performs  mathematical calculations on surrounding pixels in order to calculate  the new pixels. It may often be hard to tell the difference in results  from bicubic interpolation (e.g. in Photoshop) and dedicated programs.  Printers (and/or printer drivers) can also perform this interpolation so  you can often choose where to do it: in software or in printer,  depending on where it is done best or easiest. If there even is any  difference. Sometimes you can see a difference, sometimes not. You'll  have to try things out yourself and see what it looks like. My own  simple tests shows that the interpolation that a good photo lab do is at  least as good as the interpolation I do myself in Photoshop or  Lightroom, both when scaling up and down. For me and my demands as a  hobby photographer it's a waste of time trying to do my own  interpolation. I send the photos without resizing to the lab, and the  prints I get back look very good.

But lets assume that we want  300 PPI to get good quality even at close range. How large can we really  print? Well, it depends on how many pixels the image has. Take the four  cameras as examples again:


The formula is: size in inches=(pixels/PPI). To get size in centimeters, multiply by 2,54.


    2 megapixels (x*x pixels) at 300 PPI gives a size of ~ x*x cm
    4 megapixels (2272*1704 pixels) at 300 PPI gives a size of ~ 19*14 cm
    8 megapixels (3264*2448 pixels) at 300 PPI gives a size of ~ 28*21 cm
    10 megapixels (3872*2592 pixels) at 300 PPI gives a size of ~ 33*22 cm


Divide by 2,54 to get it in inches.


This  is at 300 PPI, which is often recommended for high quality prints. For  normal every-day use you can often go down to 200 PPI which means you  can get somewhat larger prints, but still with good enough quality.

Or  you can think in another way: if you know the size of the print, and  you know how many pixels you have, then what will the PPI become? Is it  enough, or too low?


The formula is: PPI=(pixels/size in inch). If you have the size in cm then divide it by 2,54 to get inches.

Assume  you want to print photos from the four cameras in A4-size. The long  edge of an A4 is 29,7 cm (11,7 inches) which gives the following PPI for  the four different pixel counts:


    2 megapixels (x*x pixels) at 29,7 cm edge gives PPI x (too low, the print will look pixelated)
    4 megapixels (2272*1704 pixels) at 29,7 cm edge gives PPI 194 (almost too low, but it might work)
    8 megapixels (3264*2448 pixels) at 29,7 cm edge gives PPI 279 (OK)
    10 megapixels (3872*2592 pixels) at 29,7 cm edge gives PPI 331 (very OK, actually higher than necessary)

Yet  a third way of thinking is that if you have around 8 megapixels or  more, that will generally be enough for printing at any size. With 8  megapixels you can do A4-prints (12*8 inches) at 279 PPI. If you print  larger you normally have greater viewing distance and you can get away  with a lower PPI.


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