DPI


DPI is a printing term, for “dots per inch.” Generally, photographers don’t care about this, as it is not a factor of the photo itself just how the photograph is used. However, the topic often comes up and is confusing, so here’s a primer.

“Forget about the dpi of an image. It’s pretty much irrelevant until ink hits paper. What is important? Total number of pixels.”
— iStockphoto

DPI

DPI is a printing and display term, meaning Dots Per Inch. 72 dpi is for web pages where each inch of an image requires 72 pixels. The Apple iPhone displays images at 132 dpi. 200 or 300 dpi is for printing on paper which requires a finer resolution of 200 or 300 pixels for every inch. This does not affect the file size (resolution, image size) of the photo itself, just how it is displayed.

For example, imagine a photo which is 600 pixels wide. On the Web, that would be 600/72 pixels=8.3 inches wide. That is the size of the photo above. But if I was to print that same file at 300 dpi, it would only be 600/300=2 inches wide. Same file, different size, due to a different display resolution.

My coffee-table books are 12"x10" printed at 350 dpi. So, for a full-page picture at full resolution, I would need a photo size of 12x350=4200 pixels wide, and 10x350=3500 pixels high. That’s a total of 4200x3500=14.7 million pixels. The Nikon D5100 has a sensor with 16.2 megapixels, so that’s suitable.

But what if my camera only has 6 megapixels? I can still print at 10 inches high but at a lower resolution (quality). A 6MP camera produces an image 2000 pixels high. Spread over 10 inches that is 200 dpi. Not the full resolution that could be printed but enough to look OK.

What DPI Should I Use?

As a photographer, it doesn’t matter. The image will be the same. The dpi setting is just a data field.

As a publisher, set the dpi data field to whatever you need. This may be 72 dpi for web, 200 dpi for inkjet printers, 300 dpi for prints.

I Licensed a High-Res Image But It’s Low-Res!

Is it? Whether the file says 72 dpi or 150 dpi or whatever doesn’t matter. What you want is the pixel dimensions. 3000 pixels wide and 2000 pixels high is a high-res, 6 megapixel image, regardless of the dpi setting it was saved with.

“The dpi of a file is just a way to measure it. When someone says they need a 300 dpi file, EVERY file can be measured at 300 dpi, whether is happens to be saved that way or not.”
— iStockphoto

Why Don’t Stock Agencies Use A Standard DPI?

Because resaving a JPEG image reduces its quality. Sometimes the agency can change the dpi but often it is left at whatever setting the photographer used.

PPI

PPI is Pixels Per Inch. For our purposes we’ll say that it’s the same as DPI.

PPC

I’m European and I agree that the metric system is smarter. PPC is Pixels Per Centimetre. (British spelling there!)

Up-Sizing

“Images may not be upsized more than 5% — we perform an interpolated upsize to sell the ‘supersized’ version — if you upload upsized images, you risk your account being suspended.”
— Shutterstock

You don’t want to do this if you’re uploading photos to a microstock agency.

“iStock will not accept files that have been up-sampled or “rezzed-up”. In other words, you can’t increase the pixel dimensions to be larger than the file’s native size.”
— iStockphoto

If you are controlling the printing, you can use software to “up-sample” the image to a higher resolution. This intelligently guestimates what the missing data should be. Products include Perfect Resize and PhotoZoom.

Example Sizes for Photo Files
SizePixels*Approximate Print Size*
XSmall300x4001"x 1.5" @ 72dpi
Small600x8002"x 3" @ 72dpi
Medium1200x16004" x 5" @ 300dpi
Large1920x25606" x 8" @ 300dpi
XLarge2800x42009" x 14" @ 300dpi
XXLarge3300x490011" x 16" @ 300dpi
XXXLarge3700x560012" x 18" @ 300dpi

*Sample dimensions only. Actual dimensions depend on the size of the original uploaded file.

— iStockphoto

Comments


Reply by Anonymous

April 22, 2016

I need to send a digital photo to a jury process that is 300d pi and 1000 pixels at its longest point. I just don’t know how to do that. I use an iPhone 6 for my digital photos.


Reply by Andrew Hudson, PhotoSecrets

June 7, 2016

There are many computer programs that can help. If you have a Mac, you can use Preview. Open the photo in Preview, go to Tools > Adjust Size, and, in the Width box (or Height box for a vertical image), enter ’1000’. Click OK and you are done.

There are also websites that can do this. Try a search for Free Resize Images Online.

Do not worry about the 300 DPI, that is a printing term and you are not printing the picture.


Reply by Anonymous

April 14, 2016

When I am changing my pics from 72 (what it always is at when I email myslef a pic from my camera to anyone) to 300dpi so that they can be printed, they become more pixelated. The picture is no longer sharp. I’d like to know a way to take pictures on my iPhone at 300 dpi. Is it possible or not?


Reply by Andrew Hudson, PhotoSecrets

June 7, 2016

Hi.

This is a common confusion. DPI is not a camera term but a printing term. The camera term is MP (for megapixels).

The iPhone 4S – 6 has an 8 MP camera, so you are taking 8 MP pictures on your iPhone.

When printing at 300 DPI, divide the pixels by 300 and that gives you the number of inches your print can be. For example, your 8 MP camera produces pictures that are 3264 x 2448 pixels.

3264 / 300=about 10

2448 / 300=about 8

Thus you can print your images at about 8" x 10" at full resolution.

When you email a photo, the email program probably reduces the image size to about 640 pixels or 1024 pixels. That is where the pixelation is coming from. So to print the photos, do not use the emailed files but instead use the original files from your camera.


Reply by Anonymous

November 2, 2015

Ok, I’m not "printing" any digital photo. None that I create on my iPhone or buy online. I’m using them for my website for banners or cover photos that requires sizes such as 1800 x 711. The standard printing DPI’s are not relevant here. I get a blurry image if I put an iPhone 6 picture or S, M sizes. How to address? Resizing and resolution for digital, not printing, seems to be a different beast. 1920 x 2560 is the next size up per article, yet how to fit that into 1800x 711 size without picture distortion, partial loss of image, or blurry resolution.


Reply by Andrew Hudson, PhotoSecrets

January 11, 2016

Websites generally have a maximum image size of 1024 pixels. The pictures on my website are 640 pixels wide, and standard advertising banners are 468 pixels wide (“full banner”) and 728 pixels wide (“leaderboard”). You could double (or even triple) those for “retina” display, but otherwise 1800 x 711 seems large for a website. When a file is larger than the layout, the web browser will automatically compress it to the display size.

The iPhone 6 has an 8 MP camera, creating a maximum image size of 3264 x 2448 pixels. Such full-size images would take an unnecessarily long time (and bandwidth) to display, so you should resize them (“downsample”, “optimize”) to the appropriate display size.

I resize photos in Photoshop, and also in Preview on a Mac (Tools > Adjust Size). Most image-editing programs and apps can resize images. There are also many websites that can do this for free online.

Resizing an image will make it less distinct as you are reducing the resolution. You can try using the sharpen tool in your software. This will emphasize edges, by increasing the white and black on edges. But this is generally for printing (which has a higher pixel density) and can look bad if applied too much.


Reply by SA

September 25, 2015

So, I still need to know if it’s possible to convert a 72 dpi to 300 dpi to make the 300 dpi image to be a 4" x 6" photo of the same resolution.


Reply by Andrew Hudson, PhotoSecrets

January 12, 2016

This is possible if your photos is equal to, or larger than, 1200 x 1800 pixels.

A digital photo is measured in pixels and DPI does not apply. DPI is a printing term. To see what size your digital photo can print as, divide the pixel size by the DPI.

For example, say you have a computer screen which displays images at 72 dpi. We divide your 1200x1800 pixel image by 72 dpi: 1200 / 72=16.7, and 1800 / 72=25. Thus your image can display on a computer screen at 16.7" x 25". That’s a big screen! (30" diagonal).

Printing on paper requires a higher DPI, typically 300 dpi. 1200 / 300=4, and 1800 / 300=6. So your image can be printed at 4" x 6".

To answer your question, if your image is 1200 x 1800 or larger, then yes you can convert it from 72 dpi to 300 dpi to be a 4" x 6" printed photo.


Reply by Anonymous

October 9, 2014

Thanx a lot ...

u saved my life :)


Reply by Anonymous

September 24, 2014

Hi

How can i get exact 100dpi in an image?


Reply by Andrew Hudson, PhotoSecrets

October 8, 2014

Hi,

Yes, this DPI thing is always confusing.

DPI is how many pixels are printed/displayed per inch.

DPI does not refer to the image itself, just to how it is printed. For example, say you have an image which is 300 pixels wide. You could print that image using a printer setting of 300dpi, and it would print as 1 inch wide (all 300 pixels for one inch). Or you could set your printer to print at 100 dpi, and it would print the image at three inches wide (the same 300 pixels spread over three inches, so larger but with less detail per inch). A fine-art book might print at 400 dpi, whereas a billboard may print at 15 dpi.

Photoshop allows you to set the DPI, but that just sets a tag, it does not change the image itself. Go to Image > Image Size. Under “Document Size” is a box for “Resolution.” Set that to 100 pixels/inch. Notice how the document size dimensions will change accordingly, but the pixel dimensions will not.

As a photographer, you should not need to worry about DPI, that is for printers to worry about.

Andrew


Reply by Cj18522000-programs@yahoo.com

April 18, 2014

I am a layperson, little knowledge: If appears I have data like matching an apple and orange. I have been asked to provide photos in 150 pixels wide by 200 pixels high at resolution of 72dpi. If unable to resize to at least 300 dpi. I am not able to resized. I already have photos in 8 by 10 300 DPI; 2 by 3 300 DPI; and 2 by 3 100 DPI. Question: Which of the last 3 sizes matches the 150 pixels wide and 200 pixel high 72 dpi or 300 dpi? I want to get close but I have to different measure types. Thanks


Reply by Andrew Hudson, PhotoSecrets

October 8, 2014

Hi,

The person asking you is also, apparently, “a layperson, little knowledge.”

A requirement mixing pixels with DPI is nonsense. They should ask for a pixel dimension, OR a size with DPI. They are trying to sound knowledgeable without being so.

Their request of 150 pixels by 200 pixels is a very small image. This size is OK for a webpage (where it would display at 1.5" x 2" at 100 DPI), and is generally too small for print.

The closest of your three sizes is the last one, the smallest:

2 by 3 at 100 DPI=(2 x 100) x (3 x 100)=200 pixels x 300 pixels.

A competent designer/printer would ask for the highest resolution image available. In your case, that is the first size:

8 by 10 at 300 DPI=(8 x 300) x (10 x 300)=2400 pixels x 3000 pixels.

Best wishes,

Andrew


Reply by Jenny

May 16, 2013

I’m confused. Some people want to have a print of a photo on sites where you sell photos. Does the agency change the DPI setting of your photo for this, or should we upload with a 300dpi setting ourselves.


Reply by Andrew Hudson, PhotoSecrets

September 23, 2013

Hi Jenny:

Yes, this DPI thing is confusing.

When submitting photos, the agency usually wants you to upload the highest resolution image available, so whatever came from your camera. You don’s need to change the DPI/resolution yourself.

People who download photos from microstock sites are often given a choice of size. If a person wants a 4-inch by 6-inch print, at 300 DPI, they would want to download a file size of at least 4x300=1200 pixels by 6x300=1800 pixels.

Hope that helps!

Andrew


Reply by MNHL Verschraegen

January 2, 2013

Dear reader,

This article is completely untrue. It makes a big difference when you make a picture with a 72 dpi camera or with a 300 dpi camera. When you are zooming in you will see the difference immediatly.

I suggest that you go bsg to the drawingboard and redo your homework.

Greetings,


Reply by Andrew Hudson, PhotoSecrets

January 6, 2013

72 vs 300 DPI

Hi MNHL,

Thank you for your note. Your point is correct if the subject is megapixels, such as a 2MP photo vs. a 16MP photo. As you zoom in, you will immediately see more detail in the higher resolution image.

But DPI is not a measurement of the the original image resolution. It is a printing term. It indicates how many pixels (dots) are printed in one inch. Images of any resolution can be printed at 72DPI or 300DPI. An image that is, for example, 360 pixels wide would have a width of 5 inches if printed at 72DPI or 1.2 inches at 300DPI.

Andrew


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