What is a digital image?

From the WhiteWall expert Jan-Ole Schmidt

In today's digital world, images are omnipresent. Whether on smartphones, computers or the internet - digital images play a central role in communication and everyday life. But what exactly is a digital image and what are its technical foundations? This article provides a comprehensive insight into the topic and explains the most important aspects such as the creation of a digital image, resolution, pixels, image size, PPI and DPI.

Digital images: An introduction to the basics

A digital image is essentially a visual representation of information in a form that can be processed and displayed by computers, smartphones and other digital devices. Unlike analog images, such as photographs on paper or paintings on canvas, digital images consist of a grid-like arrangement of tiny, square pixels called pixels (short for "picture element"). These pixels are the smallest components of a digital image and have a major influence on its quality, detail and sharpness.

How a digital image is created

A digital image is usually created using a digital camera, scanner or other image capture device . These devices capture the light reflected from a scene or from a document to be scanned and convert it into electronic signals. In a camera, for example, the light passes through the lens onto an image sensor (today usually a CMOS sensor, previously also CCD sensors). The sensor consists of millions of pixels (megapixels) where the light is received by light-sensitive photodiodes and converted into electrical signals.

Most image sensors are monochromatic and only capture brightness information. To capture color information, the sensor is overlaid with a Bayer color filter matrix or another color mosaic filter that equips the pixels with red, green and blue (RGB) color filters. In conjunction with the brightness information, the sensor can thus reproduce colors in different intensities in order to be able to display a broad color spectrum. This is already done in the camera or later in image processing software. The total of all pixels ultimately results in the visible image.

Digital images are not only created by recording real scenes with camera sensors or scanners, but can also be created completely virtually. Digital drawings are created using graphics tablets or drawing programs such as Adobe Fresco or Procreate, whereby the artist has full control over shape, color and texture. In 3D rendering, images are created by calculating virtual models that are created using 3D software. Light, shadows and materials are simulated to achieve photorealistic or stylized results. Another method is generation using artificial intelligence (AI), which creates completely new images based on algorithms and given data. AI systems such as DALL-E or Stable Diffusion can generate creative and often surprising digital images from text descriptions or patterns. These approaches open up new possibilities for design, art and photography beyond traditional photography.

What does resolution mean?

The resolution of a digital image refers to the number of pixels contained in an image and is usually given in the form "width x height". For example, an image with a resolution of 1,920 x 1,080 pixels contains a total of 2,073,600 pixels. A 45 megapixel photo with a resolution of 8,192 x 5,464 pixels contains 44,761,088 pixels. The resolution plays a decisive role in the sharpness and detail of an image. The more pixels there are, the more details can be displayed.

A higher resolution means a larger number of pixels, which also significantly increases the amount of information stored. High-resolution images therefore require more storage space on digital devices and require faster processing speed, especially when editing or transferring such files. This is because each pixel contains additional data such as color and brightness information that must be processed by the software or hardware. High-resolution images therefore require fast processors and large memory cards or hard disks for cameras and computers or notebooks.

Image size and its meaning

The image size refers to the dimensions of an image when it is output on a screen or print medium. The image size is often specified in inches or centimeters and results from the combination of resolution and pixel density. The pixel density indicates how many pixels per inch (PPI = "Pixels Per Inch" ) are displayed on a screen or are available for a print product. The abbreviation DPI = "Dots Per Inch" indicates how many dots per inch are printed on the print medium, also known as dot density.

Ratio between resolution and image size

• High resolution and small image size: If an image has many pixels (high resolution) but is spread over a small area, it has a high pixel density (many pixels per inch). The result is a sharp and detailed image.

• Low resolution and large image size: If an image with a low resolution (few pixels) is enlarged, the pixel density is low (few pixels per inch). This makes the pixels visible and the image appears blurred or "pixelated".

DPI: Dots Per Inch and their significance for printing

DPI, or "dots per inch", is a measure of print resolution that indicates how many dots of ink are printed within a linear inch (2.54 centimeters). A higher DPI number means that more ink dots are placed in a small area, resulting in greater detail and sharpness of the printed image. An image with 300 DPI contains 300 dots per inch, resulting in a fine and detailed image. For this reason, 300 DPI is considered the standard value for high-quality printing of photos and graphics. In contrast, images for the web are usually saved at 72 DPI, as monitors and screens do not require a higher DPI resolution. A higher DPI value for web images would only increase the file size without improving the visual quality. It therefore makes sense to adapt the DPI value of an image to its intended use.

Difference between DPI and PPI

In addition to DPI, there is also the term PPI (pixels per inch), which is often used in connection with digital images. While DPI refers to the print resolution, PPI describes the number of pixels per inch on a digital screen, but is also used to indicate how many pixels per inch of an image are available for printing . A monitor with a higher PPI number, for example, displays images more sharply and clearly. Modern smartphones and computer screens generally have a higher PPI value, which results in a better display of text and images.

The importance of file formats for digital images

Digital images can be saved in different file formats, which affect how the image data is compressed and saved. The most common formats are JPEG, PNG, TIFF, RAW and now also HEIC/HEIF . Each format has its own advantages and disadvantages, depending on the intended use of the image.

JPEG is a widely used format that is known for its efficient "lossy compression". In this case, "lossy" means that the file size is reduced compressing parts of the image data . The good news is that with low compression, i.e. when the JPEG is saved in high quality, the JPEG image file is still perfectly suitable for printing and printing out at WhiteWall. At the same time, the file is significantly smaller than an image in TIFF format, for example.

PNG uses lossless compression, which ensures that no image data is lost when the file is saved or edited. This means that the image quality is fully preserved, regardless of how many times the image is saved. The PNG format is particularly suitable for web graphics, logos and images with transparent backgrounds, as it supports alpha channels that enable transparency. Although the PNG format offers high quality, it also results in a larger file size compared to the JPEG format.

TIFF is a format widely used in professional photography and printing, as it can also be compressed without loss or uncompressed. It enables large image files to be saved in the highest quality without data loss. The ability to save multiple layers and extensive metadata makes TIFF a preferred format for post-processing photos in image editing programs. However, the files are very large, which limits their use when storage space is limited.

RAW is a format that has been specially developed for professional photographers and demanding image processing. It saves the uncompressed, unprocessed data directly from the camera sensor, which allows maximum control during post-processing. RAW files offer greater color depth and a higher dynamic range, which is particularly advantageous in post-processing, as details in shadows and highlights can be better reproduced. However, this flexibility has the disadvantage that RAW files are very large and require special software for editing and conversion to more common formats such as JPEG or TIFF.

The HEIC/HEIF format (High Efficiency Image File Format) combines high image quality with efficient data compression. Compared to JPEG and PNG, HEIC/HEIF offers greater compression, which significantly reduces the file size while maintaining or even improving image quality. A particular advantage is the support of a color depth of up to 16 bits per color channel, while JPEG is limited to 8 bits per channel. This means that images in HEIC/HEIF format can display finer color gradations and a higher dynamic range. In addition to better image quality and smaller file sizes, HEIC/HEIF supports advanced functions such as transparency, which was previously reserved primarily for the PNG format. The HEIC/HEIF format is often used in mobile operating systems such as iOS and Android, as it saves storage space and still delivers high-quality images.

The different file formats are therefore suitable for different applications: Photos in the JPEG and HEIC/HEIF formats can be saved at different compression rates and are therefore ideal in a more compressed form for email attachments, for example, but also in low compression (maximum quality setting) for high-quality printouts with a small file size. The PNG format is suitable for lossless, detailed web graphics with transparency, TIFF for professional prints of the highest quality and RAW for full control when editing images. Each option has specific advantages and disadvantages that need to be carefully weighed up to achieve the best possible quality and efficiency.

Digital image processing

Image editing plays an important role in optimizing digital images. Software such as Adobe Photoshop, GIMP or Affinity Photo allows the user to scale, crop, adjust colors, change resolution and perform many other editing steps. These programs offer tools for improving image quality and adjusting the DPI for printing. When editing images, however, care should be taken to ensure that the original image quality is not impaired too much. Excessive compression or changes to the resolution can lead to a loss of quality that cannot be reversed. It is therefore advisable to keep a copy of the original image and carefully consider what changes should be made.

For the best possible image quality, it is advisable to edit the images in RAW format, as it contains the most image information of all image formats and therefore offers the greatest scope for creativity. Another important factor is the color depth. Images with a color depth of 16 bits provide 65,536 levels per color channel red, green and blue (RGB) in RGB mode. An 8-bit file, on the other hand, only delivers 256 tonal value levels. This means that with a higher number of bits, significantly better color gradations and therefore smoother color transitions can be displayed. For printing, the images are then best saved either as a JPEG in high quality or as a TIFF file. WhiteWall also offers so-called soft proofs, with which the color reproduction on a specific paper can be simulated on the monitor. The images can then be specifically optimized for the planned paper type. For more information on image preparation for printing and imaging with WhiteWall, please refer to chapter 1.3 Image optimization for printing, Automatic image optimization with WW.

Conclusion:

Digital images have become an integral part of modern life and understanding their basic properties is crucial to fully exploit their quality and potential applications. Whether you're a professional photographer, a graphic designer or just an interested amateur looking to expand your knowledge, a good understanding of the basics from resolution to DPI to compression will help you make your projects more efficient. So it's worth taking a closer look at these technical details to optimize your work and ensure that your images are as impressive on screen as they are on paper. Present your most beautiful pictures, for example, with a high-quality WhiteWall wall art behind acrylic glass. With our new Changeable Magnetic Frames you can also exchange your pictures quickly and easily. For vacation memories and wedding reportages, we also recommend our WhiteWall Coffee Table Book with high-quality photo paper and finishing on the cover.