When we are printing, it is necessary to prepare the relevant design files in advance. Pixels per inch has a significant impact on your image design. Many people may have heard of PPI, but they are not clear about its specific meaning. In this blog, we will systematically introduce the meaning of pixel per inch and explain how many pixels per inch for printing. In addition, we will also supplement other knowledge related to pixels per inch.
Table of Contents:
The Meaning of PPI in Screen Displays
The Meaning of PPI in Printing
For Photo Printing
For Book Printing
For Poster Printing
For Large Outdoor Billboard Printing
- How to Find the PPI of an Image
- How to Change the PPI for Printing
- FAQs about Pixels Per Inch for Printing
What’s the Meaning of Pixels Per Inch
Pixels per inch(PPI) is a unit of pixel density, representing the number of pixels per inch on a display. This concept is derived from DPI. The higher the PPI value, the greater the density at which the display can render images. This also means images can be rendered with higher realism.
In fact, the meaning and function of PPI vary slightly across different contexts. The most common applications of PPI are in screen displays and printing.
The Meaning of PPI in Screen Displays:
When applied to screens (such as mobile phone screens, computer monitors, etc.), PPI describes the pixel density of the screen hardware itself. In this context, the PPI value directly determines the clarity perceived by the human eye when viewing the screen.
Screen PPI is fixed and can be calculated using the following formula:
PPI = √(x² + y²) ÷ z
Where x and y represent the horizontal and vertical pixel counts respectively, and z represents the screen diagonal length (in inches).
The Meaning of PPI in Printing:
When referring to PPI in the printing field, PPI is a measure of digital image resolution, indicating the number of pixels in a 1-inch square of a digital image. It determines the level of detail and sharpness when printed.
The PPI in printing is adjustable and determined by both the total number of pixels in the image file and the physical dimensions of the print.
Total Image Pixels = Print Dimensions (inches) × PPI
Here are the common sizes and pixels at different PPI, which can help you quickly determine relevant information.
| Size (Inches) | 180 PPI | 240 PPI | 300 PPI |
|---|---|---|---|
|
4×6 |
720×1,080 |
960×1,440 |
1,200×1,800 |
| 5×7 |
900×1,260 |
1,200×1,680 |
1,500×2,100 |
| 8×10 |
1,440×1,800 |
1,920×2,400 |
2,400×3,000 |
| 11×14 |
1,980×2,520 |
2,640×3,360 |
3,300×4,200 |
| 16×20 |
2,880×3,600 |
3,840×4,800 |
4,800×6,000 |
What’s the Relation Between PPI and DPI
As mentioned earlier, the concept of pixels per inch (PPI) is derived from dots per inch(DPI). In fact, this derivation is primarily evident in the printing field.
In the printing field, DPI refers to the number of ink dots a printer can produce within an inch. The PPI and DPI are interdependent in printing. You can think of DPI as the print output, and PPI as the digital input. An image’s PPI must match the printer’s DPI to ensure optimal print quality.
This video can help you better understand PPI and DPI.
How Many Pixels Per Inch for Printing
In fact, the choice of pixels per inch depends on the image quality you desire. Generally speaking, the minimum value for good print quality is 180 PPI. For better image quality, you can use 240 PPI. And if you want the highest possible quality, you may need to use 300 PPI. Actually, when selecting a specific PPI value, you need to consider the printed item and the viewing distance. Some specific PPI values for printing are as follows for your reference.
For Photo Printing
When printing photos, selecting 300-400 PPI is most suitable. Since photos are typically viewed at close range, this demands higher print quality. A higher PPI makes photos appear more vivid and lifelike.
For Book Printing
When printing books, you can opt for 250-300 PPI. Since books are typically read at close range, a higher PPI is preferable. However, because text constitutes a significant portion of books, selecting 250-300 PPI strikes an optimal balance between text clarity and image vibrancy.
For Poster Printing
150-200 PPI is ideal for printing posters. Generally, posters are viewed from a distance of 1-2 meters. The farther the viewing distance, the lower the PPI requirement. A 150 PPI poster looks excellent when viewed from 1 meter away.
For Large Outdoor Billboard Printing
For printing large outdoor billboards, the requirements for PPI are relatively low. Generally speaking, large outdoor billboards are typically placed near highways. Viewers are positioned at a considerable distance from the billboards. Therefore, you can opt for a lower PPI value. Typically, 72-150 PPI is sufficient to achieve a perfect display effect.
How to Find the PPI of an Image
You can calculate the PPI of an image using the formula we mentioned earlier (Total Image Pixels = Print Dimensions × PPI), or you can directly view the PPI value in the image file.
For Windows:
- First, locate your image in File Explorer or on your desktop.
- Next, right-click the image and select “Properties”.
- Last, go to the “Details” tab to find the resolution.
For Mac:
- Open the Finder application from the toolbar.
- Navigate to your file.
- Right-click the file and select “Open With” > “Preview”.
- Click Tools and choose “Show Inspector”.
- Retrieve your PPI details from the displayed list.
How to Change the PPI for Printing
By changing the PPI, you can make your images more suitable for printing. You can choose various software to make the adjustments. The operation processes of different software are similar. Most of them only differ in the positions of the operation buttons. Here is the process of changing the PPI in Photoshop.
1. Open the Image: Go to Photoshop, and click on the “File” option in the menu bar. Then open the image you want to adjust.
2. Go to the Image Setting: You need to choose Image > Image Size in the menu bar. This will bring up a window showing the current width, height, and resolution.
3. Change PPI: Locate the “Resolution” column and enter the desired new PPI value.
4. Decide Whether to Resample: At the bottom of the “Image Size” window, you will see a checkbox labeled “Resample”.
- If you uncheck the “Resample” option, Photoshop will lock the total pixel count. When you change the PPI, the actual size of the image will be adjusted accordingly, but the image quality remains unchanged.
- If you check the “Resample” option, you can freely adjust the PPI and pixel size. Photoshop will add or remove pixels based on the new PPI.
5. Save Your Image: After completing the above settings, click the “Confirm” button and then save your image again.
FAQs about Pixels Per Inch for Printing
1. In the printing field, does a higher PPI always lead to better results?
The answer is uncertain. In fact, the PPI value needs to be determined based on the purpose and dimensions of the printed material. In photo printing, a higher PPI value does indeed lead to better results. However, in other fields, such as large outdoor billboard printing, an excessively high PPI will only increase the file size and processing burden.
2. Why is 300 PPI the best choice for photo printing?
The printed photos are often viewed up close. 300 PPI can effectively display images that are often viewed closely. At this density, the human eye cannot distinguish individual pixel points at the normal reading distance, so the image appears very smooth and sharp.
3. How should I set the PPI for my printing project?
You can follow the following steps to set the PPI:
- First, you need to determine the size of the printed product.
- Based on the purpose of the printed item and the viewing distance, select the PPI value.
- Calculate the required pixel size. (Total Image Pixels = Print Dimensions x PPI)
- Ensure that your original image is at least this pixel size.
- When creating a new project in software (such as Photoshop, etc.), directly input the corresponding PPI value.
4. Can increasing PPI make blurry images clearer?
Increasing PPI cannot make blurry images clearer. PPI determines the pixel density of the image. The higher the PPI, the more pixels there are in a unit area, and it will be displayed more delicately theoretically. However, the blur problem is usually caused by the pixel arrangement or the quality of the image itself. Simply increasing the PPI value cannot eliminate these fundamental problems.
Conclusion
Pixels per inch has multiple meanings. In the field of printing, pixels per inch and print dimensions jointly determine the clarity and details of the printed product. You need to select the appropriate PPI value based on the purpose of the printed product. The appropriate PPI can make your design more in line with your expectations and enable the printed product to fulfill its intended function.
