For Capture, Photoshop Editing, and Printing
File formats affects two things, the size of the files stored (i.e. how much room it takes up on the memory card or disk) and the image quality. Both of these are affected by how much or how little the file format uses compression.
Compression reduces the file size by eliminating redundant information. It is done to reduce storage space and speed up transmission when uploading or emailing images. The trade-off is of course; by reducing the file size the quality is affected. There are 2 types of compression, lossy and lossless.
Lossy permanently eliminates information and reconstructs the image each time it is reopened. It is used to obtain highly compressed, small files.
Lossless compresses information, but doesn’t throw away original data.
There are several types of formats, but in this class we are only concerned with the following 4:
JPEG (.jpg)- lossy. (Joint Photographic Experts Group) is a universal compression standard and all digital cameras can save in JPEG format. It is also one of the standard formats for images posted on the web, used in Word documents and PowerPoint presentations, and is usually required by most commercial digital printers (such as Costco or Walgreen’s). JPEG compresses photos for small file size and fast transmission, but highly compressed images show distortion due to image loss from the compression.
Another problem with its compression scheme is that each time an image is opened and re-saved, more data is lost and cannot be recovered. Because it is capable of compressing images to quite small file sizes, it’s the most common form of file that is used by digital cameras. However, the problem of compression and re-compression leaving “artifacts” suggests that digital camera images that will be manipulated and saved again should be saved in a format other than JPEG (like TIFF) to avoid degrading quality by resaving in JPEG.
When to use: For on-screen viewing of pictures, images emailed or uploaded to the web, when an image is not going to be opened and resaved frequently, or when space is at a premium, JPEG works very well. If you need to send it to a commercial printer, do your edits with TIFF or PSD, when your editing is finished save a JPEG version.
PSD (.psd)- LOSSLESS. This format is used while working in Adobe Photoshop. It saves Layered images as well as those without Layers. It is also a good format for general saving, as it is fast. Photoshop is a lossless format, meaning there is no loss of image quality.
When to use: Use this format as a standard “in editing progress” file saving format. It’s a good format for pictures that are destined to be printed by home printers or professional labs.
TIFF (.tif)- LOSSLESS. (Tag Image File Format) A universal format for PC and MAC users, acceptable to many professional labs, and, most widely used for publishing and printing. It renders high quality images, which makes it one of the two best all-around formats in Photoshop. TIFF’s main attractions are its lossless compression (no loss of image quality), and it integrates well with nearly every word processing and page-layout software. TIFF (as of Photoshop version 7 and above) can also save documents that contain layers.
There are several options in the “TIFF Save” dialog box. The Byte Order allows you to save in PC or Mac format. It also gives you the option of having LZW compression on or off. LZW compression is just like using Stuffit or Zip-it on the file, and is a lossless form of compression.
When to use: Use this format whenever you need lossless image quality and want to compress your file a bit. It’s a good format for pictures that are destined to be printed by home printers or professional labs.
RAW/DNG- LOSSLESS. RAW (brand specific ex. Canon’s .CR2, Nikon’s .NEF) is similar to a latent image on film. When used to capture an image it retains all the information that the camera captured and is unprocessed in a smaller resolution version, but can hold greater bit depth. In other words, it contains all the information that was captured before any post-capture processing by the camera’s software. JPEG and TIFF process the image by correcting for tone, color, sharpness, and white balance before saving it on the memory card. RAW will render the highest quality results and allow the photographer to be in complete control of the image from capture to presentation without any uncontrolled processing. RAW will also give you smaller file sizes than the camera’s TIFF. DNG (digital negative) is a way to save all the RAW information and is considered universal, rather than the brand specific RAW files.
So how do you choose which format? Determine the quality you need based on your output. Will it be viewed in print form or on the monitor? Low quality JPEG images will work great for this instance. If you are making a high quality print, shoot in RAW or TIFF and in Photoshop save as a PSD or TIFF.
For image capture basically it comes down to weighing the quality of the image to the amount of memory. RAW gives you the highest quality and complete control. TIFF (if your camera offers it, very few do) is lossless but uses up more memory. JPEG is universal and compresses images to a small size, but some quality is sacrificed.
For editing and processing in Photoshop use Photoshop or the TIFF file formats. They save quickly, allow you to save selections and layers, allow you to save 16-bit images, and are lossless so you will get the highest quality.
For Internet and email use JPEG. For commercial printing save a separate JPEG format file, which is a smaller file size and will transmit faster. Remember though, it is lossy so you will lose some quality and information. Not for editing/processing in Photoshop.