The path to perfect printing: What matters when it comes to image quality

From the WhiteWall expert Jan-Ole Schmidt

When an image is transferred from the digital to the physical world, i.e., when it is printed or exposed, the image quality must meet different requirements than when viewed on a smartphone or monitor. This article explains which factors, such as image resolution, DPI, image size, and viewing distance, are crucial for optimal printing results. It also explains in more detail how to upload images for our WhiteWall products to ensure that the image quality meets the desired requirements.

The interplay between resolution and DPI

Image resolution is one of the most important aspects when it comes to the print quality of digital images. It specifies how many pixels an image consists of, usually as width x height (e.g., 6,000 x 4,000 pixels). A higher resolution means more detail and usually better quality. However, resolution alone does not guarantee perfect printing. The decisive factor is how these pixels are distributed across the print area.

People often talk about DPI here, for example, a resolution of 300 DPI. However, the correct unit here is PPI, since assessing the resolution of image data for photo printing is about how many pixels of the photo are available per inch (2.54 cm), not about how many ink dots are placed on the print. For viewing at close range—for example, when holding small-format prints in your hand—300 PPI is optimal. The printer’s actual resolution is usually much higher. For wall art in larger formats, however, a lower resolution is often sufficient, since these pieces are not viewed at close range. For more information, see the section "Relationship between DPI and viewing distance."

Examples of the relationship between resolution, PPI, and print image size

The physical image size at which a digitally captured image can be printed in high quality depends on the camera's resolution and the PPI value (which is often referred to as DPI in software, however).

Example 1:

A 24-megapixel image has a resolution of approximately 6,000 x 4,000 pixels. If this image is printed at a print resolution of 300 PPI, the following physical image size results: The calculation is (6,000 pixels / 300 PPI) x (4,000 pixels / 300 PPI), which equals 20 x 13.33 inches. Converted, this is approximately 51 x 34 centimeters, which roughly corresponds to the DIN A3 format.

Example 2:

To print images in larger formats such as DIN A2 or even DIN A1, a camera with a higher sensor resolution is recommended. A 60-megapixel image with a resolution of approx. 9,504 x 6,336 pixels ( ) offers more leeway here. With a print resolution of 300 PPI, this results in an ideal print size of approximately 31.68 x 21.12 inches. Converted, this is about 80 x 54 centimeters, allowing for significantly larger prints up to just under DIN A1 (84.1 x 59.4 cm). A slight enlargement to DIN A1 would hardly affect the image quality.

Relationship between PPI and viewing distance

The required PPI value also depends on the viewing distance. For large prints, such as wall art, which are viewed from a greater distance, the PPI resolution can be lower, as shown in our example with a 24-megapixel image at 200 PPI: The calculation is (6,000 pixels / 200 PPI) x (4,000 pixels / 200 PPI), which results in a print size of approximately 76 x 51 centimeters instead of the 51 x 34 centimeters calculated above at 300 PPI. The enlarged image would still look good from a viewing distance of about two meters, as the lower PPI resolution is not noticeable from this distance.

What should you keep in mind when printing smartphone photos?

When printing smartphone images in coffee table books or on wall art, several factors must be taken into account in order to achieve the best possible print quality. Here, too, image resolution, print resolution in PPI, and image compression play a key role.

For example, the iPhone 15 Pro’s 48-megapixel camera takes photos with a resolution of 8,000 x 6,000 pixels. Assuming a relative resolution of 300 PPI—so that the images remain sharp even when viewed from a short distance—the ideal output size for a 48-megapixel photo is calculated as follows: Using (8,000 pixels / 300 PPI) x (4,000 pixels / 300 PPI), the image can be printed at a size of approximately 68 x 34 centimeters for the best possible quality. This is more than sufficient for our Coffee Table Book in DIN A4 and DIN A3 formats.

If you take photos with the iPhone 15 Pro's wide-angle camera, the calculation is slightly different. Here, the resolution is twelve megapixels or 4,272 x 2,848 pixels. If we convert this resolution to 300 PPI, the output size is approximately 36 x 24 centimeters. The resolution of 12 megapixels is therefore definitely sufficient for full-page images in our A4 coffee table book. But is the resolution also sufficient for high-quality, full-page prints in an A3 coffee table book? The good news is that yes, there is no need to worry here either. If you place a 12-megapixel image on a full-page DIN A3 page, the print resolution is equivalent to 258 PPI. The difference to 300 PPI is so small that you will hardly notice any loss of quality.

If you want to print images from your smartphone, you should always make sure that the images are in their original resolution and with low compression. When sending images by email or via messenger services such as WhatsApp, the images are often automatically reduced in size and compressed to make them easier to send. In this case, it is worth asking the sender for the original image.

Check image quality at WhiteWall

If you want to present your images as a high-quality WhiteWall wall art behind acrylic glass, as a large-format print, or as a photo display, you can use the WhiteWall configurator on our homepage to check whether the image quality is sufficient for the desired output medium. The configurator is located at the top of our WhiteWall website and is started by clicking the "Upload photos" button. First, the digital image is uploaded and displayed in a preview in the configurator. The quality indicator shows whether the resolution of the image is sufficient for the desired output size.

Since multiple images are uploaded for coffee table books and photo calendars, we take a slightly different approach here. These products can be designed either online or on your own computer using our WhiteWall download software. If the resolution of an image is not sufficient for the selected size format after it has been placed on a coffee table book or calendar page, a warning is automatically displayed. This warning helps to avoid unpleasant surprises and ensure that the end product meets expectations.

Upscaling images

It is also possible to enlarge the image beyond the determined optimal output size. In print processing, we can also interpolate, i.e., insert a color gradient between two adjacent pixels. This allows images to be enlarged to such an extent that they can no longer be printed in "very good" quality, but still in "good" quality. Doubling the image size (1:2 interpolation) is often unproblematic with high-quality data and is hardly noticeable visually. So if the image is originally sufficient for an optimal maximum size of 20 x 30 centimeters, enlarging it to 40 x 60 centimeters is perfectly acceptable and usually unproblematic. This is especially true if, for example, it is wall art that will be viewed from a greater distance. In this case, the enlargement is less noticeable.

If you are unsure whether the image resolution and selected image size are optimally harmonized for printing, we recommend requesting a test print of the future product. This minimizes the risk and allows for a realistic assessment of the print quality.

Conclusion:

At first glance, the image quality requirements for printing appear diverse and complex. Image resolution, DPI or PPI, image size, and viewing distance play a decisive role in achieving optimal printing results. Our user-friendly upload process at WhiteWall helps you meet these requirements and ensure that the quality of the printed image meets your expectations.

If you take the above aspects into account when preparing your images for printing and follow the recommendations for resolution and image size, nothing will stand in the way of a high-quality print result. Whether it's a photo canvas, large-format print, or wall art under acrylic glass—with the right preparation and the right tools, your digital images can be brought to life in brilliant quality on paper or other media.