working with digital images

Display Resolution

-Every monitor and screen has a specific resolution. As mentioned above, an HD display has a resolution of 1920 x 1080 pixels. A 4K display has twice the resolution of HD, or 3840 x 2160 pixels. It is called "4K" since the screen is nearly 4,000 pixels across horizontally. The total number of pixels in a 4K display is 8,294,400, or just over eight megapixels. -Monitor resolution defines how many pixels a screen can display, but it does not describe how fine the image is. For example, a 27" iMac 5K display has a resolution of 5120 x 2880 while an older 27" Apple Thunderbolt Display has exactly half the resolution of 2560 x 1440. Since the 27" iMac is the same physical size as the Thunderbolt Display but has twice the resolution, it has twice the pixel density, measured in pixels per inch, or PPI.

Lossless Compression

-Lossless compression reduces a file's size with no loss of quality. This seemingly magical method of reducing file sizes can be applied to both image and audio files. While JPEGs and MP3s use lossy compression, newer compression algorithms, such as JPEG 2000 and Apple Lossless compression, can be used to create lossless compressed files. -Lossless compression basically rewrites the data of the original file in a more efficient way. However, because no quality is lost, the resulting files are typically much larger than image and audio files compressed with lossy compression. For example, a file compressed using lossy compression may be one tenth the size of the original, while lossless compression is unlikely to produce a file smaller than half of the original size.

Lossy Compression

-Lossy file compression results in lost data and quality from the original version. Lossy compression is typically associated with image files, such as JPEGs, but can also be used for audio files, like MP3s or AAC files. The "lossyness" of an image file may show up as jagged edges or pixelated areas. In audio files, the lossyness may produce a watery sound or reduce the dynamic range of the audio. -lossy compression removes data from the original file, the resulting file often takes up much less disk space than the original. For example, a JPEG image may reduce an image's file size by more than 80%, with little noticeable effect.

raster graphics

-Most images you see on your computer screen are raster graphics. Pictures found on the Web and photos you import from your digital camera are raster graphics. They are made up of grid of pixels, commonly referred to as a bitmap. The larger the image, the more disk space the image file will take up. -JPEG and GIF are the most common compressed image formats on the Web, but several other types of image compression are available. Raster graphics can typically be scaled down with no loss of quality, but enlarging a bitmap image causes it to look blocky and "pixelated."

Image Resolution

-A digital photo that is 3,088 pixels wide by 2,320 pixels tall has a resolution of 3088 × 2320. Multiplying these numbers together produces 7,164,160 total pixels. Since the photo contains just over seven million pixels, it is considered a "7 megapixel" image. Digital camera resolution is often measured in megapixels, which is simply another way to express the image resolution.

PNG file format

-PNG, which can be pronounced "ping" or "P-N-G," is a compressed raster graphic format. It is commonly used on the Web and is also a popular choice for application graphics. -PNG includes many of the benefits of both GIF and JPEG. PNG images use lossless compression like GIF files, so they do not have any blurring or other artifacts that may appear in JPEG images. The PNG format also supports 24-bit color like the JPEG format, so a PNG image may include over 16 million colors. -the PNG format supports an alpha channel, or the "RGBA" color space. The alpha channel is added to the three standard color channels (red, green, and blue, or RGB) and provides 256 levels of transparency. -it is not suitable for all purposes. For example, digital photos are still usually saved as JPEGs, since PNGs take up far more disk space. GIFs are still used for animations since PNG images cannot be animated.

resolution

-Resolution measures the number of pixels in a digital image or display. It is defined as width by height, or W x H, where W is the number of horizontal pixels and H is the number of vertical pixels. For example, the resolution of an HDTV is 1920 x 1080.

JPEG file format

-Stands for "Joint Photographic Experts Group." JPEG is a popular image file format. It is commonly used by digital cameras to store photos since it supports 224 or 16,777,216 colors. The format also supports varying levels of compression, which makes it ideal for web graphics. -The 16 million possible colors in a JPEG image are produced by using 8 bits for each color (red, green, and blue) in the RGB color space. -Besides image data, JPEG files may also include metadata that describes the contents of the file. This includes the image dimensions, color space, and color profile information, as well as EXIF data. -While the JPEG format is great for storing digital photos, it does have some drawbacks. For example, the lossy compression can cause an issue called "artifacting," in which parts of the image become noticeably blocky. This typically happens when a high compression setting is used to save the image. For saving small images and images with a lot of text, the GIF format is often a better alternative. JPEG images also don't support transparency. Therefore, the JPEG format is a poor choice for saving non-rectangular images, especially if they will be published on webpages with different background colors.

vector graphics

-Unlike JPEGs, GIFs, and BMP images, vector graphics are not made up of a grid of pixels. Instead, vector graphics are comprised of paths, which are defined by a start and endpoint, along with other points, curves, and angles along the way. A path can be a line, a square, a triangle, or a curvy shape. These paths can be used to create simple drawings or complex diagrams. -Because vector-based images are not made up of a specific number of dots, they can be scaled to a larger size and not lose any image quality. -Vector graphics are ideal for logos, which can be small enough to appear on a business card but can also be scaled to fill a billboard. Common types of vector graphics include Adobe Illustrator, Macromedia Freehand, and EPS files.

media compression

-the goal of media compression is to reduce file size and save disk space. However, media compression algorithms are specific to certain types of media, such as image, audio, and video files. -Three of the most common include JPEG, GIF, and PNG. JPEG compression, which is commonly used for digital photos, incorporates a lossy compression algorithm that averages nearby colors and removes color variations that are imperceivable by the human eye. GIF compression reduces the color palette of an image to 256 colors or less, which provides an efficient way to represent each color within the image. PNG compression uses a lossless compression algorithm that filters the image data and predicts pixel colors based on other nearby pixels. -Most video files are also compressed. Popular video formats, such as MPEG and DivX compress video using a specific codec. Each codec uses a custom algorithm that removes redundant information from the video.