Image file formats
Photoshop offers a wide variety of image file formats including BMP, JPEG, PNG, TIFF, and PICT. It can also save in PDF format and, open, and edit files already saved as PDFs. RAW files imported from a digital camera can be opened and edited by Photoshop. In addition to all this, Photoshop has its own file format, PSD. Saving as a PSD file will preserve adjustments and layers without flattening the image, but this type of file can only be opened in Photoshop.
Formats for the Web
The best formats for web use are JPEG and PNG because they significantly compress the size of the file. If a PNG file is very large and will take a long time to load, it can be saved with interlacing.
JPEG files – A warning
Saving a file in JPEG allows it to be greatly compressed and is good for making small image files that still have high resolution and good color quality, particularly for use on the internet. However, JPEG removes information from the image each time it is re-compressed: every time a file is saved as a JPEG, every time a file is opened, edited and changes are saved, or every time “save as” is used to save a file as a JPEG. The amount of information lost depends on the compression of the image. JPEG images will never retain the quality of the original image. TIFF and PNG are better file formats for preserving all information in a digital image.