How to understand DPI and PPI correctly - Easy Beginners Tutorial / Worst Myths cleared up

Introduction to DPI and PPI

In this section, the speaker introduces the topic of DPI (dots per inch) and PPI (pixels per inch) and addresses common misconceptions about them.

Understanding DPI and PPI

• Misconception: Setting an image to 300 dpi ensures good print quality. This is not true.

• Misconception: Images for websites or screens should be set to 72 dpi. This is also not true.

• Pixels and colors do not have a physical size. They only acquire a size when you view or print an image.

• DPI (dots per inch) and PPI (pixels per inch) are used to assign a pixel size when viewing or printing an image.

Resolution and Output Resolution

• The term "resolution" is often used interchangeably for two different things: output resolution and image resolution.

• Output resolution refers to the physical resolution of your screen or print, while image resolution refers to the number of pixels in your file.

Different Methods of Setting DPI

Non-Destructive Method

• In this method, the number of pixels remains the same, but the dpi value changes.

• Example: An image with 1000 pixels can be assigned a dpi value of 100, resulting in a 10-inch wide image with a 100 dpi output resolution.

Destructive Method (Resampling)

• In this method, the original image is destroyed, and a new image is created with a different pixel count.

• Example: An image with 1000 pixels can be resized to fit into a one-inch picture with 100 dpi, resulting in the loss of 900 pixels.

Debunking Myths

• Myth: Lower dpi images have lower quality. The culprit is actually resampling, where pixels are intentionally discarded.

• Myth: Images for websites or screens should be set to 72 dpi. This myth originated from older screens that had a fixed dpi value. Today, screen sizes and resolutions vary widely.

Printing and DPI

• Myth: Images need to be set to 300 dpi before printing. The required dpi depends on the viewing distance and desired detail.

• Viewing distance determines how many dpi are needed for optimal image quality.

Conclusion

In this section, the speaker concludes by emphasizing the importance of understanding DPI and PPI and debunking common misconceptions.

• Understanding DPI and PPI is crucial for accurately setting image resolutions for different purposes.

• Misconceptions about DPI and PPI can lead to misinformation about image quality.

• It's important to consider factors such as viewing distance when determining the appropriate resolution for an image.

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New Section

This section discusses the concept of DPI (dots per inch) and its impact on image resolution. It explains how DPI can be lower for larger images that are viewed from a distance, and higher for smaller images viewed up close. The material on which an image is printed also affects the optimal DPI value.

Understanding DPI

• Images with lower DPI can still appear crisp when viewed from a distance due to the compression of information within a smaller field of vision.

• The material on which an image is printed determines the optimal DPI value. A smooth surface allows for higher DPI, while a coarse surface requires lower DPI.

New Section

This section demonstrates the practical application of DPI in Affinity Photo software. It shows how changing the canvas size and resolution affects image quality.

Working with Affinity Photo

• A file with 72 dpi resolution and large dimensions is opened in Affinity Photo.

• Creating a new document with a small print size (A10) at 300 dpi.

• Importing the original image into the new document and resizing it to maintain as many original pixels as possible.

• Despite having a higher dpi canvas, the resized image appears pixelated due to its low resolution.

• Exporting the file as PDF for print, maintaining 300 dpi rasterization.

• The exported PDF file has significantly reduced file size compared to the original pixel image.

New Section

This section explores why downsampling occurs during export despite selecting "nothing will be rasterized" in Affinity Photo's export dialog.

Downsampling During Export

• Despite selecting "nothing will be rasterized," downsampling occurs during export because this option only applies to text and vector shapes, not pixel information.

• Affinity Photo allows flexibility in resizing and rotating images within the canvas without requiring manual calculations for pixel-perfect 300 dpi output.

• The only consideration is ensuring that the pixel resolution of the image is sufficient to cover the desired print space at the chosen dpi.

New Section

This section emphasizes that pixels do not have a size, and DPI determines the number of pixels per inch. It explains two methods of setting DPI: non-destructive and destructive resampling.

Understanding DPI and Resampling

• A pixel does not have a size; DPI represents pixels per inch.

• Two methods of setting DPI: non-destructive (maintaining original pixel information) and destructive (resampling).

• Determining the required DPI for print depends on how far away the print will be viewed.

• Affinity Photo handles the conversion to 300 dpi automatically, eliminating the need for manual calculations.

• The key consideration is ensuring sufficient pixel resolution to cover the desired print space at the chosen dpi.