This week’s question comes from Frank Sreshta who asks:
Do megapixels matter when printing images? I am wanting to print large metal prints and canvas, maybe 24×24 at most, maybe bigger. I am currently shooting with a Nikon d500 and shot in Raw.
The short answer to this is yes, megapixels do matter when it comes to printing, but the megapixels don’t matter as much as they used to.
If you’re not aware, megapixel means one million pixels, and the megapixel count for your camera tells you how many pixels make up the images you capture.
In Frank’s case, the D500 is 20.9 megapixels, or, 20,900,000 pixels, and you can actually verify this for any camera by taking the image dimensions and multiplying them. (when you do that, you’ll also see how manufacturers play with numbers)
The D500 produces images that are 5568 pixels by 3712 pixels.
5568 x 3712 = 20,668,416 or 20.7 megapixels.
(That difference of 200,000 pixels is a bit of marketing bs and a bit of a technical limitation.)
Now, when it comes to printing, what is actually most important is the pixel density of the image, which is given as the DPI or PPI of the image. (I have a video that covers this topic, you can click here to watch it)
DPI is an acronym for Dots Per Inch
PPI is an acronym for Pixels Per Inch
These terms are pretty interchangeable. The difference is that DPI refers to printed images, while PPI refers to digital images. (For simplicity’s sake, in the rest of this email I’ll use PPI regardless of whether I’m talking about print or digital)
What these terms refer to is exactly as they describe, they tell you how many pixels are contained in one measured inch of the image.
This is critical to printing because the human brain needs a certain density of pixels in order to be able to see the image as an image, instead of as a bunch of dots.
Let’s look at an example.
The photo below has a pixel density that allows our brains to see the image, rather than the pixels that make up that image.
This next image is the same image, but with a MUCH lower pixel density, low enough that the brain can’t see the image without also seeing the pixels that make up that image.
So when it comes to printing, you have to consider not just how many pixels you have in your image, but what the ideal pixel density is for the intended use of the image.
For printing, generally speaking, 300 PPI is the ideal pixel density. This gives you prints that look the way you expect a print to look, instead of looking like a bunch of ink dots on a piece of paper.
Now, to bring this back around to Frank’s question, the number of megapixels in your image dictates the native print size of your image. To figure out the native print size of any image, you just need to do a bit of simple math.
Let’s look at the D500 again, which has an image resolution of 5568 x 3712 (20.6 Megapixels)
So here’s what we know:
- We’re printing the image, so we want 300 PPI
- The image has 5568 pixels on the long edge
- The image has 3712 pixels on the short edge
To figure out how big you can print the image you take each pixel dimension and divide by your desired pixel density (PPI)
5568 / 300 = 18.56
3712 / 300 = 12.4
What that tells us is that if we set up the image so that the pixel density is 300 PPI, when printed, the image will be 18.56 inches x 12.4 inches (47.14cm x 31.5cm).
Now let’s say Frank wanted to print an image that was 24 inches by 36 inches.
Here’s where Megapixels don’t matter to printing. You can print any image at just about any size you want, you just have to adjust the pixel density.
You can print the D500 image at 24 x 36 by setting the pixel density to 155 PPI.
To find that 155 PPI is also just a bit of math. You take the length in pixels and divide it by the desired length in inches to get the PPI.
5568 / 36 = 154.7 (rounding up to 155)
So the key to printing is resolution AND PPI.
We know that 155 is not an ideal pixel density, so in order to print the image at 24 x 36 and have a workable pixel density you’d need to add pixels to the image, which you can do by enlarging the image using software like Photoshop or Affinity Photo.
Doing the enlargement is actually pretty easy, and I actually show how it’s done in Photoshop in this video here. (The video reviews what I’ve covered in this email, and at the 6:00 mark shows how to do the enlargement.)
When you do an enlargement like this the software has make up new pixels to fill in the image, so after the D500 image to print 24 x 36 at 300 PPI, you’d have an image that’s 10,800 pixels x 7200 pixels.
And what’s great is that modern software, coupled with modern cameras with 16+ megapixels, you can pretty easily print just about any size you want. You may have to do a little work in your image editor to get it ready for print, but it’s easy enough to do. (To give you an example, back when I still had my 8 Megapixel Canon Rebel XT, I was able to print beautiful 20 in x 30 in prints after enlargement)
If you have any questions about this or anything else photography related, hit reply and let me know!
One last thing, last week I made a mistake in the email on Exposure Compensation. At one point in the email I said that while in Shutter Priority, the camera would set the shutter speed for you, which is incorrect. When in Shutter Priority mode, you set the shutter speed and the camera sets the aperture for you. (thank you to everyone who let me know! I missed that one while proofing).
Now get out there and take some damn photos!