About file formats and compression
Graphics file formats differ in the way they represent image data (as pixels or vectors), in compression techniques, and which Photoshop features they support. With a few exceptions (for instance Large Document Format (PSB), Photoshop Raw, and TIFF), most file formats cannot support documents larger than 2 GB.
Note:
If
a supported file format does not appear in the appropriate dialog
box or submenu, you may need to install the format’s plug‑in module.
About file compression
Many file formats use compression to reduce the file size of bitmap images. Lossless techniques compress the file without removing image detail or color information; lossy techniques remove detail. The following are commonly used compression techniques:
- RLE (Run Length Encoding)
- Lossless compression; supported by some common Windows file formats.
- LZW (Lemple-Zif-Welch)
- Lossless compression; supported by TIFF, PDF, GIF, and PostScript language file formats. Most useful for images with large areas of single color.
- JPEG (Joint Photographic Experts Group)
- Lossy compression; supported by JPEG, TIFF, PDF, and PostScript language file formats. Recommended for continuous-tone images, such as photographs. JPEG uses lossy compression. To specify image quality, choose an option from the Quality menu, drag the Quality pop‑up slider, or enter a value between 0 and 12 in the Quality text box. For the best printed results, choose maximum-quality compression. JPEG files can be printed only on Level 2 (or later) PostScript printers and may not separate into individual plates.
- CCITT
- A family of lossless compression techniques for black-and-white images, supported by the PDF and PostScript language file formats. (CCITT is an abbreviation for the French spelling of International Telegraph and Telekeyed Consultive Committee.)
- ZIP
- Lossless compression; supported by PDF and TIFF file formats. Like LZW, ZIP compression is most effective for images that contain large areas of single color.