One of the most challenging aspects of designing large format printed items is working with photos. Two of the most common questions asked of designers and printers regarding photos to be used in large format print design are:
“How large a photo do I need?” and “How large can I make this photo I already have?”
There is an incredible amount of confusion about these seemingly simple questions. Terms and numbers like DPI, resolution, PPI, upsizing, resampling, megabytes, file size and image size often leave clients--and sometimes even seasoned designers and printers--feeling perplexed. We’d like to make this easier for you.
THE BASICS
A digital photo is made up of pixels which are tiny squares pieced together to form an image. Depending on how a photo was created, or how it has been changed by the time you get it, an image can consist of a large or small number of pixels.
The number of pixels in a digital image, measured in width and height, is the most important factor in determining how large it can be printed while still maintaining image quality.
The statement above is the key. Digital photos are actually measured in pixels, much like a piece of paper is measured in inches or centimeters. A small photo might be 120 pixels wide by 60 pixels tall, usually shown as simply 120x60 pixels. A large image could be 7500x2500 pixels or more. Find the dimensions in pixels and you’ve unlocked the first part of this picture puzzle. Luckily it is easy to do.
Finding the measurements of a photo in pixels:
As we mentioned, dimensions will typically be shown as follows: 2400x1200 pixels. Width is generally the first number, height the second (width x height).
If you are purchasing your photos on a stock photo website, the pixel dimensions of an image should be listed in the photo specifications. (eg: dimensions = 2400x1200 pixels)
For digital photos already on a Windows computer, use the mouse to right-click on the photo. At the bottom of the pop-up menu click ‘properties.’ Under the ‘details’ tab you will find the width and height in pixels for that particular image.
For digital photos already on a Mac, use the mouse to control-click / right-click on the photo to bring up the ‘get info’ pop-up menu. Under the ‘more info’ section you will find the width and height in pixels for that particular image.
RESOLUTION AND PPI
The next piece of the puzzle involves a term we’ve all heard before: resolution. In order for an image to look sharp or print clearly, we need to keep the pixels small. The smaller the pixels, the higher the resolution. At a minimum the pixels should be small enough such that they can’t be seen by the naked eye, otherwise an image will look blurry or even ‘pixelated’. See the sample photos at the end of this article to get a better sense of what we mean.
Without getting too technical, for our purposes here, the term we need to know for resolution is PPI or pixels per inch.
smaller pixels = more pixels per inch = higher PPI number = higher resolution
There is a photo at the end of this article that shows that smaller the size of the pixels, the more pixels per inch, the higher the resolution or PPI. If we’ve lost you here, don’t worry, the theory is less important than the ability to figure out what will look good when printed, and you’ll soon be able to do just that. One last thing about resolution. You will likely encounter the use of the both PPI (pixels per inch) and DPI (dots per inch) in digital photography. Some use the terms interchangeably, but for digital photos and large format printing, we will stick with PPI.
THE BASIC EQUATION
So now we know that photo dimensions are measured in pixels but we still need to figure out how that translates into physical dimension like inches and centimeters. We use a very simple little equation to do this:
# of pixels wide / # of pixels per inch (PPI) = width in inches
# of pixels high / # of pixels per inch (PPI) = height in inches
Example: a photo which is 2400x1200 pixels, when at 300ppi the photo physically measures
2400 pixels / 300ppi = 8 inches wide
1200 pixels / 300ppi = 4 inches high
Yes, that’s it. Take the # of pixels, divide by the PPI value you require in order to get a good print (we provide a guide below) and you now know how large your existing photo can be printed.
THE IDEAL SCENARIO:
“How large a photo do I need?”
When you set out to create a large format piece, your ideal starting point is to first determine the purpose and use of your poster, sign or banner. Knowing the purpose and use will help you decide how large the printed piece needs to be, which in turn determines the size requirements of your photos. At this point you are asking yourself the “how large a photo do I need?” question.
1. Assume you are designing a poster. First determine the overall size you want or need the poster to be. Let’s say 18”x24” as an example.
2. Next, answer the following question: from what distance will the item be viewed? The closer the item will be to the viewer, the higher the resolution or PPI value you will want for any photo(s) to print at optimal quality. When in doubt, use 300ppi. That being said, if you need to lower your ppi value to make your photo larger, the following information can be used as a guide.
Default of any photo to ensure optimal print quality: 300ppi
Photo is viewed up close or ‘in-hand’: 300ppi
Photo is viewed from one to ten feet away: 150ppi (higher if possible)
Photo is viewed from more than ten feet away: see ‘Tradeoffs’ below
3. Use the formula to determine size in pixels needed for optimal printing:
Example: an 18”x24” poster will be viewed up close with a photo covering 100% of the poster.
18” wide x 300ppi = 5400 pixels wide
24” high x 300ppi = 7200 pixels high
So our photo should be at least 5400x7200 pixels for optimal print quality when being viewed up close or in-hand.
A TYPICAL SCENARIO:
“How large can I make this photo I already have?”
Often you are faced with the situation where you already have a photo that you need to work with and now you need to know how large you can make it while still maintaining print quality. The same theory applies, your equation just changes a bit:
1. Find the measurement in pixels of your existing image (refer to a previous section if you need help here). For this example you determine that your photo is 3600 x 2400 pixels.
2. Find the required resolution using the guide from the previous example:
Default of any photo to ensure optimal print quality: 300ppi
Photo is viewed up close or ‘in-hand’: 300ppi
Photo is viewed from one to ten feet away: as low as 150ppi
Photo is viewed from more than ten feet away: see ‘Tradeoffs’ below
3. Use the formula to determine size in inches that you can print while maintaining optimal quality.
2400 pixels wide / 300ppi = 8” wide
3600 pixels high / 300ppi = 12” high
So your photo can be used at 8”x12” while still maintaining optimal print quality.
Now let’s say you are making a large overhead banner, and you want to use that same 2400x3600 pixel photo, but you need to make it physically larger than 8”x12”. You know the banner will be up in the air and only be viewed from at least 10 feet away. Now you can use a different PPI value.
2400 pixels wide / 150ppi = 16” wide
3600 pixels high / 150ppi = 24” high
Note that you don’t have to jump straight from 300ppi to 150ppi. If you do the calculation at 200ppi and the photo will be big enough for you, then do just that. In general, try to keep your PPI value as high as possible. That said, don’t worry about trying to go higher than 300ppi as this appears to be the limit that the human eye can distinguish in commercially printed material.
TRADEOFFS
The information above provides the photo sizing guidelines to create an optimal quality poster, banner or sign. For very large pieces, it can be difficult to find a photo large enough. More often the challenge you face is that you have an existing photo that you would really like to use in the piece even though it is not quite big enough. In these instances, you may have to accept that by using a resolution lower than 300ppi, you’ll be trading off some image clarity when viewed up close. The great thing about large format printing is that in most cases, people don’t view these items ‘in-hand’ like a magazine or other small printed item, so if it will be viewed from far away, your viewer will not be able to see the difference. If you climbed up and looked at a massive roadside billboard normally viewed from 100 feet away, you would see that the pixels are huge and easy to see individually, perhaps with a value as low as 10ppi. This is why it is so beneficial to know or think about how your viewer will be looking at the item.
SOME OTHER NOTES ABOUT PHOTO QUALITY
In all of the scenarios above, we are assuming you are starting with a ‘good’ photo. A good photo is one that has been properly shot with good lighting and stability and that has not been compressed either by your camera settings, using digital zoom, or re-sampled using photo editing software. If you are taking your own photos, set your resolution to the highest value possible. Also beware that some email programs automatically and drastically reduce photos size when sending, but you are often given a warning before this happens.
WHEN IN DOUBT, CONTACT US
If you are working with a photo and simply aren't sure, definitely feel welcome to contact us. You can send us the photo and we’ll be able to give you some guidance on how far you can push it. Our large format print software and work flow is set up to make your photos look as good as they possibly can, and it can indeed make up for some quality issues, so we will be able to help you make that judgement call. Further, if you’re not comfortable taking the risk, and need to see it printed, we can always send you a printed proof first.
© Cathy Vandergeest, RGD, gawck group inc.
“How large a photo do I need?” and “How large can I make this photo I already have?”
There is an incredible amount of confusion about these seemingly simple questions. Terms and numbers like DPI, resolution, PPI, upsizing, resampling, megabytes, file size and image size often leave clients--and sometimes even seasoned designers and printers--feeling perplexed. We’d like to make this easier for you.
THE BASICS
A digital photo is made up of pixels which are tiny squares pieced together to form an image. Depending on how a photo was created, or how it has been changed by the time you get it, an image can consist of a large or small number of pixels.
The number of pixels in a digital image, measured in width and height, is the most important factor in determining how large it can be printed while still maintaining image quality.
The statement above is the key. Digital photos are actually measured in pixels, much like a piece of paper is measured in inches or centimeters. A small photo might be 120 pixels wide by 60 pixels tall, usually shown as simply 120x60 pixels. A large image could be 7500x2500 pixels or more. Find the dimensions in pixels and you’ve unlocked the first part of this picture puzzle. Luckily it is easy to do.
Finding the measurements of a photo in pixels:
As we mentioned, dimensions will typically be shown as follows: 2400x1200 pixels. Width is generally the first number, height the second (width x height).
If you are purchasing your photos on a stock photo website, the pixel dimensions of an image should be listed in the photo specifications. (eg: dimensions = 2400x1200 pixels)
For digital photos already on a Windows computer, use the mouse to right-click on the photo. At the bottom of the pop-up menu click ‘properties.’ Under the ‘details’ tab you will find the width and height in pixels for that particular image.
For digital photos already on a Mac, use the mouse to control-click / right-click on the photo to bring up the ‘get info’ pop-up menu. Under the ‘more info’ section you will find the width and height in pixels for that particular image.
RESOLUTION AND PPI
The next piece of the puzzle involves a term we’ve all heard before: resolution. In order for an image to look sharp or print clearly, we need to keep the pixels small. The smaller the pixels, the higher the resolution. At a minimum the pixels should be small enough such that they can’t be seen by the naked eye, otherwise an image will look blurry or even ‘pixelated’. See the sample photos at the end of this article to get a better sense of what we mean.
Without getting too technical, for our purposes here, the term we need to know for resolution is PPI or pixels per inch.
smaller pixels = more pixels per inch = higher PPI number = higher resolution
There is a photo at the end of this article that shows that smaller the size of the pixels, the more pixels per inch, the higher the resolution or PPI. If we’ve lost you here, don’t worry, the theory is less important than the ability to figure out what will look good when printed, and you’ll soon be able to do just that. One last thing about resolution. You will likely encounter the use of the both PPI (pixels per inch) and DPI (dots per inch) in digital photography. Some use the terms interchangeably, but for digital photos and large format printing, we will stick with PPI.
THE BASIC EQUATION
So now we know that photo dimensions are measured in pixels but we still need to figure out how that translates into physical dimension like inches and centimeters. We use a very simple little equation to do this:
# of pixels wide / # of pixels per inch (PPI) = width in inches
# of pixels high / # of pixels per inch (PPI) = height in inches
Example: a photo which is 2400x1200 pixels, when at 300ppi the photo physically measures
2400 pixels / 300ppi = 8 inches wide
1200 pixels / 300ppi = 4 inches high
Yes, that’s it. Take the # of pixels, divide by the PPI value you require in order to get a good print (we provide a guide below) and you now know how large your existing photo can be printed.
THE IDEAL SCENARIO:
“How large a photo do I need?”
When you set out to create a large format piece, your ideal starting point is to first determine the purpose and use of your poster, sign or banner. Knowing the purpose and use will help you decide how large the printed piece needs to be, which in turn determines the size requirements of your photos. At this point you are asking yourself the “how large a photo do I need?” question.
1. Assume you are designing a poster. First determine the overall size you want or need the poster to be. Let’s say 18”x24” as an example.
2. Next, answer the following question: from what distance will the item be viewed? The closer the item will be to the viewer, the higher the resolution or PPI value you will want for any photo(s) to print at optimal quality. When in doubt, use 300ppi. That being said, if you need to lower your ppi value to make your photo larger, the following information can be used as a guide.
Default of any photo to ensure optimal print quality: 300ppi
Photo is viewed up close or ‘in-hand’: 300ppi
Photo is viewed from one to ten feet away: 150ppi (higher if possible)
Photo is viewed from more than ten feet away: see ‘Tradeoffs’ below
3. Use the formula to determine size in pixels needed for optimal printing:
Example: an 18”x24” poster will be viewed up close with a photo covering 100% of the poster.
18” wide x 300ppi = 5400 pixels wide
24” high x 300ppi = 7200 pixels high
So our photo should be at least 5400x7200 pixels for optimal print quality when being viewed up close or in-hand.
A TYPICAL SCENARIO:
“How large can I make this photo I already have?”
Often you are faced with the situation where you already have a photo that you need to work with and now you need to know how large you can make it while still maintaining print quality. The same theory applies, your equation just changes a bit:
1. Find the measurement in pixels of your existing image (refer to a previous section if you need help here). For this example you determine that your photo is 3600 x 2400 pixels.
2. Find the required resolution using the guide from the previous example:
Default of any photo to ensure optimal print quality: 300ppi
Photo is viewed up close or ‘in-hand’: 300ppi
Photo is viewed from one to ten feet away: as low as 150ppi
Photo is viewed from more than ten feet away: see ‘Tradeoffs’ below
3. Use the formula to determine size in inches that you can print while maintaining optimal quality.
2400 pixels wide / 300ppi = 8” wide
3600 pixels high / 300ppi = 12” high
So your photo can be used at 8”x12” while still maintaining optimal print quality.
Now let’s say you are making a large overhead banner, and you want to use that same 2400x3600 pixel photo, but you need to make it physically larger than 8”x12”. You know the banner will be up in the air and only be viewed from at least 10 feet away. Now you can use a different PPI value.
2400 pixels wide / 150ppi = 16” wide
3600 pixels high / 150ppi = 24” high
Note that you don’t have to jump straight from 300ppi to 150ppi. If you do the calculation at 200ppi and the photo will be big enough for you, then do just that. In general, try to keep your PPI value as high as possible. That said, don’t worry about trying to go higher than 300ppi as this appears to be the limit that the human eye can distinguish in commercially printed material.
TRADEOFFS
The information above provides the photo sizing guidelines to create an optimal quality poster, banner or sign. For very large pieces, it can be difficult to find a photo large enough. More often the challenge you face is that you have an existing photo that you would really like to use in the piece even though it is not quite big enough. In these instances, you may have to accept that by using a resolution lower than 300ppi, you’ll be trading off some image clarity when viewed up close. The great thing about large format printing is that in most cases, people don’t view these items ‘in-hand’ like a magazine or other small printed item, so if it will be viewed from far away, your viewer will not be able to see the difference. If you climbed up and looked at a massive roadside billboard normally viewed from 100 feet away, you would see that the pixels are huge and easy to see individually, perhaps with a value as low as 10ppi. This is why it is so beneficial to know or think about how your viewer will be looking at the item.
SOME OTHER NOTES ABOUT PHOTO QUALITY
In all of the scenarios above, we are assuming you are starting with a ‘good’ photo. A good photo is one that has been properly shot with good lighting and stability and that has not been compressed either by your camera settings, using digital zoom, or re-sampled using photo editing software. If you are taking your own photos, set your resolution to the highest value possible. Also beware that some email programs automatically and drastically reduce photos size when sending, but you are often given a warning before this happens.
WHEN IN DOUBT, CONTACT US
If you are working with a photo and simply aren't sure, definitely feel welcome to contact us. You can send us the photo and we’ll be able to give you some guidance on how far you can push it. Our large format print software and work flow is set up to make your photos look as good as they possibly can, and it can indeed make up for some quality issues, so we will be able to help you make that judgement call. Further, if you’re not comfortable taking the risk, and need to see it printed, we can always send you a printed proof first.
© Cathy Vandergeest, RGD, gawck group inc.
