Monitor resolution, print resolution
The resolution of a monitor varies greatly from one device to another. Smartphone, tablet or computer monitor, how does it change the display of images? Can we anticipate the resolution and quality of a print from its observation on a monitor?
DPI, PPI
When we talk about resolution, two numbers associated with dpi often show up: 72 and 300. 72 dpi is associated with monitors, 300 dpi with printing. Dpi stands for dots per inch, ppi for pixels per inch. In this article, we will speak mainly about pixels and we will thus use the term ppi.
Manufacturers mention the size and resolution of a monitor in relation to its diagonal. If the resolution is calculated according to the length of the display, the difference is often tiny. On this 27-inch iMac, it is 219 dpi (diagonal) and 217 dpi (length).
The term resolution is used to specify how many pixels are displayed on a monitor. The iMac 27 in. Retina has 5120 x 2880 pixels. Resolution is also used to define how many pixels per inch a monitor can display : divide the number of pixels by the number of inches of the diagonal or length of a monitor.
From Smartphone to Computer Monitor
A smartphone, tablet or computer monitor display resolutions that can be very different. An iPhone 12 Pro Max has a resolution of 458 ppi. The Samsung S9 goes up to 568 ppi. The iPad Pro, with a much larger surface area than a smartphone, has 264 ppi. Computer monitors don’t reach the high resolution of a smartphone, but can compete with a tablet. The Dell UltraSharp 32 UltraHD 8K (7680 x 4320 pixels) is the champion with 280 ppi for 32 inches. A 13-inch MacBook Pro M2 (2560 x 1600 pixels) has 227 ppi. The same monitor size, for example 27 inches, can be manufactured with several resolutions: an iMac 5K displays 217 ppi (5120 x 2880 pixels), a Viewsonic VA2719-2K-SMHD WQHD (2560 x 1440 pixels), 108 ppi. An Asus VA27DQ Full HD (1920×1440 pixels), 82 ppi. These resolutions are calculated in relation to the diagonal of the monitor. If we refer to the length of the monitor rather than the diagonal, the resolution does not change much, within 2 or 3 pixels. So where does the 72 ppi come from? This setting corresponded to a standard use with the cathode ray tube monitors, but it’s very rare with LCD panels.
27 in. Resolutions
Let’s go back to a 27-inch device. It is a very comfortable size for photo editing. A 27-inch monitor with a 16:9 ratio has a display width about 60 cm. Let’s do the following experiment. I am looking at a 3000-pixel long image on a 27-inch 5K resolution. Its resolution is 217 ppi. If the image is displayed at 100%, in Lightroom or Photoshop, it will be 3000/217 in length. This corresponds to 13.82 in. or 35.1 cm. On a 27-inch 4K (3840 x 2160 pixels) monitor at 163 ppi, its length will be 3000/163, or 18.40 in. or 46.7 cm. On a 27-inch WQHD (2560 x 1440 pixels) monitor at 108 ppi, its length will be 27.78 inches, or 70.6 cm. In the latter case, the image at 100% cannot be displayed in full on the monitor.
An image of 3000 pixels long displayed at 100% on a monitor with a resolution of 217 ppi is 35 cm long. It is displayed in its entirety on a 27-inch iMac that is 5120 pixels long.
The same 3000-pixel long image displayed at 100% on a 108 ppi resolution monitor is almost 70 cm long. It is therefore cropped on a 27-inch screen with a length of 2560 pixels.
By reducing the display size to 50% on the 108 ppi resolution monitor, the image is reduced to 35 cm long. The display resolution becomes equivalent to twice that, at 216 ppi.
Printing Resolution
After talking on the resolution of the monitor, let’s move on to the printing resolution. We print images at 300 ppi so that the prints provide a good rendition of details. And also because a large part of printers use a native resolution of 300 ppi. If an image is sent to the printer with a different resolution, it will systematically be resampled to 300 ppi. Most Epson printers up to A2 size (notably the SC-P series) use a native resolution of 360 ppi.
Comparison of Monitor and Print
Computer monitors cannot display images at 300 or 360 ppi, although the Dell UltraSharp 32 UltraHD 8K is not far off with its 280 ppi. If we had monitors at 300 or 360 ppi, we could simulate with good fidelity the details and sharpness we can expect from a print. But we can bypass this situation. If a 27-inch 4K monitor delivers 163 ppi, the image displayed at 50% simulates this resolution twice higher, at 326 ppi. We are therefore very close to 300 and 360 dpi. With a 27-inch WQHD at 108 ppi, a display at 50% shows 216 ppi and 432 ppi at 25%. One could select an intermediate display factor, say 36.5% to reach 300 ppi, but percentages that differ from 50% and 25% often show losses in image sharpness due to pixel display interpolation. In fact, from experience, we have found that a 100% display on a monitor that delivers a resolution higher than 200 ppi simulates the detail of a print at 300 or 360 dpi quite well. If the monitor is around 100 ppi, a 50% image does the job. However, since a monitor and a print are two different media, the sharpness and transition of details cannot be observed with the same visual acuity.
Discover the photography courses at Spéos
Spéos offers various training courses ranging from simple one-week photography courses (initiation and advanced level) to 3-year courses. The long courses to become professional photographers allow you not only to master all the photographic techniques and its vocabulary (blurs, hyperfocus, sharpness zone, depth of field, backlighting, focal length, shutter release, autofocus, wide-angle, rule of thirds, etc.), but also all the stages of shooting and image processing.
Visiting the school allows you to discover the premises, the studios and the equipment, and is undoubtedly the best way to familiarize yourself with your future way of working. This is why, in addition to the open days, Spéos offers throughout the year personalized visits by appointment to come and discover the school with a member of the team.
Text and photos: Philippe Bachelier, teacher of Printing techniques at Spéos
