Image File Formats - Which to Use?
- Photoshop (.psd)
- Tagged Image File Format or TIFF (.tif)
- Joint Photographic Experts Group or JPEG (.jpg)
Let’s start with Photoshop (.psd). This format is proprietary to Adobe software (Photoshop, Illustrator, Pagemaker, etc.). The big advantage of this format is that with it you can save Photoshop layers. This is very important if you are working on a complex image with multiple layers (image, text, shape, etc.). Save your working copies in .psd format and you can open them later and still retain all the layers. The .psd format will not compress the file so it will be quite large.
Next we have the Tagged Image File Format or TIFF (.tif). This is an uncompressed (or losslessly compressed) format that is very useful for storing and archiving unlayered imagery. TIFFs can be opened in numerous graphic programs on both Mac and PC platforms. When saving an image as a TIFF, there is an option for LZW compression. I would recommend using this as it is a lossless form of compression that often reduces the file size substantially. I save all non-layered digital images that pass through the Photo Lab at their full resolution (either from camera or scanner) as LZW compressed TIFFs. Actually, 16 bit files don’t seem to benefit from LZW compression so only use it with 8 bit files.
Last and least (in size) is Joint Photographic Experts Group or JPEG (.jpg). JPEG is a lossy compressed file format. It is extremely versatile as it can greatly reduce the size of a graphics file, thus allowing it to be used on the web or sent attached to an e-mail. JPEGs are cross platform and cross program. When saving a file as a JPEG you can choose the amount of compression desired for the image. The greater the compression, the smaller the file size, but at a price. When compressed, information about color and tonality are discarded permanently. A compressed file may exhibit blotchiness around objects with fine detail and color banding instead of smooth gradations of tone. For these reasons you should store an archived version of each image as an uncompressed JPEG or LZW compressed TIFF that you can always return to.
My recommendation for saving digital image files is:
- Open up all digital images (either from scanner or camera) in Photoshop.
- Make tonal and color adjustments and then save as a TIFF with LZW compression at full resolution. If you are working with 16 bit files, save as TIFF without LZW compression. If lack of storage space is a problem then save as an uncompressed JPEG. This will be your archived original that you can always return to.
- To prepare this image for the web or Powerpoint presentation, open the archive file, resize to desired specifications and save in a different location as a JPEG with compression.
There are several other file formats you might run into including PNG, GIF, PICT, EPS, RAW, and Genuine Fractals to name a few. There is much information on the web about these formats. If you're interested in researching this subject further, here are some links:
- JPEG info
- JPEG 2000 info
- PNG (Portable Network Graphics) info
- TIFF info
- RAW image format info
- Genuine Fractals info