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Digital Printing Explained 1 – MegaPixel (Image Resolution) vs Print Size

In this series we will be looking into the printing process, and how to get images; from the camera, into the computer, and printed.  This post will focus on the first part, how to get images from the camera and how the camera contributes to the printing process.

How many Mega Pixels do I really need?

Today, camera consumers are bombarded with spec based marketing, where bigger Mega Pixels (MP) implies better quality and demands more money.  The question we always get is, "How do these big MP numbers correlate to the final print?".  While there are some great reasons to have more pixels available, when printing, more does not always equal better.  The first and most useful aid is the standard print size to resolution chart.

While this chart is a useful guide, the final application of the print will determine what ppi is required.  The two biggest factors that determine minimum ppi are printer type and distance from the print (application).  A great example of this is the difference between an 5"x7" photo, 18"x24” poster and a 14’ x 48’ billboard.  The expectation is that the 5"x7" photo will be held at no more than 12"-14" away for viewing, while the poster will be several feet or more away and the billboard will be hundreds of feet away.  The human eye's ability to distinguish dot density (resolution) is based in part on distance from the print, so the further the viewer is from the print, the lower the resolution (ppi) requirements for a satisfactory print.

Note: The chart uses ppi (Pixels Per Inch), which should not be confused with printing resolutions like 1440dpi (Dots Per Inch).  This difference will be explained later.

Mega Pixels Typical Image Resolution Size @300ppi Size @200ppi Size @150ppi
3MP 2048 x 1536 6.82" x 5.12" 10.24" x 7.68" 13.65" x 10.24"
4MP 2464 x 1632 8.21" x 5.44" 12.32" x 8.16" 16.42" x 10.88"
6MP 3008 x 2000 10.02" x 6.67" 15.04" x 10.00" 20.05" x 13.34"
8MP 3264 x 2448 10.88" x 8.16" 16.32" x 12.24" 21.76" x 16.32"
10MP 3872 x 2592 12.91" x 8.64" 19.36" x 12.96" 25.81" x 17.28"
12MP 4290 x 2800 14.30" x 9.34" 21.45" x 14.00" 28.60" x 18.67"
16MP 4920 x 3264 16.40" x 10.88" 24.60" x 16.32 32.80" x 21.76"
24MP 6048 x 4032 20.16" x 13.44" 26.90" x 16.32" 35.87" x 24.13"
36MP 7360 x 4912 24.53" x 16.37" 30.24" x 20.16" 40.32" x 26.88"
For posters and larger prints a 100-200ppi image typically produces a very useable print.  For photos that will be viewed up close, 200-300ppi is required to produce the full photo realistic appearance.  As the chart shows, even a 4-8MP camera is capable of producing very useable photo realistic prints at 8"x10" and smaller.

This creates the next logical question "So why would you need a higher MP camera?".  While a 4-8MP camera can produce excellent prints up to 8"x10", you will need the whole image to have the pixel density to produce the print which removes the option to crop.  Think about how often you take a picture only too realize that the subject isn't quite where you want it, or there is a detail/defect in the image that you only noticed when viewing the on the computer.  While many Professional Photographers will prefer to get the composition right and use the whole image, for many amateur/hobby photographers the option to crop an image allows minor composition adjustments after the fact that can make or break the final product.  At 16MP you can get a photo realistic 8"x10" print from a crop that only makes up 25% of the total image, think of it as digital after zoom.

A higher MP image also can be helpful for future prints.  As digital images do not degrade over time, a higher MP image gives the option of larger or higher resolution prints in the future.  It is always easier to not use the extra data in a 36MP image for a print than it is to try and expand a 6MP image to fill a poster.

As a final note, picking a camera based solely on the MP number is a mistake.  Higher MP does not directly equal better image quality.  Many factors such as; Sensor size (Full Frame 35mm, Crop, Micro Four Thirds, Cell Phone), pixel size/density, sensor/camera image color depth and lens quality, play an important role in getting a clean image.  As with most things, there are tradeoffs with sensor size and pixel density. Typically, smaller pixels that are tightly packed will result in reduced low light performance, more digital noise and lower dynamic range which will lower overall image quality while larger pixels with more room on the sensor will reduce noise and increase low light performance.  This results in many inexpensive point and shoot cameras (and cell phones) with very high MP numbers and tiny sensors, and expensive professional grade cameras with large, many times lower MP sensors that produce higher quality images overall.  When choosing a camera, it is important to look at more than just the number of pixels that the sensor sees and look at the performance of the camera system as a whole.  Remember, print quality starts with image quality.

Our next post in this series will focus on Image Pixels Per Inch (ppi) vs Printer Dots Per Inch (dpi).

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