Thank you to Patrick Coughlin for this essay on digital images
The art world is finally catching up to the pace set by digital technology. Unfortunately, the speed of its proliferation has made it difficult to set up an agreed upon standard. Formal writing has its clear traditions of writing formats such as MLA or Chicago style; regrettably no clear guideline has been set for digital portfolio submissions. Consequently, there is a lot of talk about DPI, resolution, RGB vs. CMYK, .TIFF vs. .JPG and much more. Thankfully there is some commonality to many of the differing submission requirements. Whether you have clear guidelines for submitting or you are creating your own promotional packet there are many aspects to take into consideration.
Image File Types
Any discussion on file formats must first begin with an introduction to the two major file compression types that all major file formats fall into.
Lossless compression algorithms reduce file size with no loss in image quality, though they usually do not compress to as small a file as a lossy method does. When image quality is valued above file size, lossless algorithms are typically chosen.
Lossy compression algorithms take advantage of the inherent limitations of the human eye and discard information that cannot be seen. Most lossy compression algorithms allow for variable levels of quality (compression) and as these levels are increased, file size is reduced. At the highest compression levels, image deterioration becomes noticeable. This deterioration is known as compression artifacting.
JPEG (Joint Photographic Experts Group) files are a lossy format (in most cases). The DOS filename extension is JPG, although other operating systems may use JPEG. Nearly all-digital cameras have the option to save images in JPEG format. The JPEG format supports 8-bit-per-color – red, green, and blue, for 24-bit total – and produces relatively small file sizes. The compression when not too severe does not detract noticeably from the image. But JPEG files can suffer generational degradation when repeatedly edited and saved. Photographic images may be better stored in a lossless non-JPEG format if they will be re-edited in future, or if the presence of small “artifacts” (blemishes), due to the nature of the JPEG compression algorithm, is unacceptable. JPEG is also used as the image compression algorithm in many Adobe PDF files.
TIFF (Tagged Image File Format) is a flexible image format that normally saves 8 or 16 bits per color – red, green and blue – for a total of 24 or 48 bits, and uses a filename extension of TIFF or TIF. TIFF’s flexibility is both a feature and a curse, with no single reader capable of handling all the different varieties of TIFF files. TIFF can be lossy or lossless. Some types of TIFF files offer relatively good lossless compression for bi-level (black and white, no grey) images. Some high-end digital cameras have the option to save images in the TIFF format, using the LZW compression algorithm for lossless storage. The TIFF image format is not widely supported by web browsers. TIFF is still widely accepted as a photograph file standard in the printing industry. TIFF is capable of handling device-specific color spaces, such as the CMYK defined by a particular set of printing press inks.
RAW refers to a family of raw image formats that are options available on some digital cameras. These formats usually use a lossless or nearly-lossless compression, and produce file sizes much smaller than the TIFF formats of full-size processed images from the same cameras. Unfortunately, the raw formats are not standardized or documented, and differ among camera manufacturers. Many graphic programs and image editors may not accept some or all of them, and some older ones have been effectively orphaned already. Adobe’s Digital Negative specification is an attempt at standardizing a raw image format to be used by cameras, or for archival storage of image data converted from proprietary raw image formats.
The PNG (Portable Network Graphics) file format is regarded, and was made as, the free and open-source successor to the GIF file format. The PNG file format supports true color (16 million colors) whereas the GIF file format only allows 256 colors. PNG excels when the image has large areas of uniform color. The lossless PNG format is best suited for editing pictures, and the lossy formats like JPG are best for final distribution of photographic-type images because of smaller file size.
GIF (Graphic Interchange Format) is limited to an 8-bit palette, or 256 colors. This makes the GIF format suitable for storing graphics with relatively few colors such as simple diagrams, shapes, logos and cartoon style images. The GIF format supports animation and is still widely used to provide image animation effects. It also uses a lossless compression that is more effective when large areas have a single color, and ineffective for detailed images or dithered images.
The BMP file format (Windows bitmap) is used internally in the Microsoft Windows operating system to handle graphics images. These files are typically not compressed, resulting in large files. The main advantage of BMP files is their wide acceptance, simplicity, and use in Windows programs.
It doesn’t take an advanced understanding of the jargon in digital imaging to know that some file types are better suited for digital portfolios. .JPEG is one of the most widely used formats due to its relative ease of use and minimal file degradation. This format is ideal for websites or sending via e-mail when there is a possibility of a slow Internet connection. .TIFF is quite possibly the best method of saving your digital files; it can be edited multiple times without file degradation and is the format that is most often used by publications. The only problem is that file sizes remain large and take up much more space on a hard drive than other file extensions.
Image resolution describes the detail an image holds. The term applies equally to digital images, film images, and other types of images. Higher resolution means more image detail. The most common term used when dealing with digital resolution is DPI (dots per inch) and PPI (pixels per inch). The difference between DPI and PPI is where they function. DPI is a measure of printing resolution and PPI is a measurement of resolution on a computer display. Essentially the higher your DPI, the more dots of color, detail, line, etc that can exist in a square inch. Higher resolution means less file compression and larger file sizes.
RGB vs CMYK Color Models
A color model describes the colors we see and work with in digital images. Each color model, such as RGB, CMYK, represents a different method (usually numeric) for describing color.
CMYK short for cyan, magenta, yellow, and key (black) and is often referred to as process color or four color. CMYK is a subtractive color model, used in color printing, also used to describe the printing process itself.
RGB color model is an additive color model in which red, green, and blue light are added together in various ways to reproduce a broad array of colors. The name of the model comes from the initials of the three additive primary colors, red, green, and blue.
Therefore, depending on what you are submitting for, different color modes are required. If you are submitting for inclusion into a publication a CMYK color profile could be requested instead of the more common RGB color profile.
The most common requirements for digital submission go as follows:
All submissions must be on a single CD. The CD/DVD should be sent in a paper sleeve in an 8 x 10 envelope, with your name and email on the CD, the sleeve, and the envelope.
For the files on your disk:
All still images must be RGB color in TIFF or JPEG format and can be no larger than 5 megabytes each. Name and number all files 00_LastnameFirstname.tif (e.g., 12_PatrickCoughlin.tif) or 00_LastnameFirstname.jpg (e.g., 13_PatrickCoughlin.jpg). Number your images in the order you wish to have them viewed. Include with your digital submission a printed, hard-copy image inventory page headed with your name. The inventory page should indicate, by corresponding number, the title, date and media of each work.