In this tutorial I will explain in short what all the photoshop formats are, and when you should use them, and when not

PSD, PDD – A PSD file is the proprietary layered format used by Adobe. It stands for Photoshop Document and is designed to take advantage of Photoshop’s layer blending options. A PDD file is similar in structure and is almost equally compatible with a PSD. It originated as the default file type for Adobe PhotoDeluxe until 2002 and was then adopted as a secondary file format for Photoshop.

BMP, RLE, DIB – Bitmap files were developed by Microsoft as an uncompressed image format. Being uncompressed, the files are typically much larger than other common file types. Bitmaps can also be saved as a DIB file. DIB is device-independent bitmap and is used in the Microsoft graphics subsystem (GDI). Bitmap quality is based somewhat on the color depth. Higher color depths (16- and 24-bit) are more detailed but also larger in size. Lower depths (4- and 8-bit) are smaller but have less colors. 4-bit images contain 16 possible colors and 8-bit contain 256. RLE images are an older technology and only support black and white images. They were replaced with GIF’s by CompuServe.

GIF- Graphics Interchange Format images are a from of bitmap designed to be much smaller files. Using compression and the limitation of only 256 colors, GIF images are well-suited for use on the internet where speed can be an issue. Invented by CompuServer, GIF images also support animation by setting up seperate frames, each with their own color pallete, and then play them in sequence. Gifs are slowly being replaced by higher quality formats such as PNG.

EPS – Encapsulated Postscript files support a combination of vector* graphics and bitmaps. Photoshop, however, rasterizes the vector graphics converting them to pixels. EPS fles come in a variety of types. DCS 1.0 files, Desktop Color Seperations, allows the saving of color seperations. DCS 2.0 files can export spot channels. EPS is similar in its limitations to the TIFF format, including the requirement to flatten all layers. It is also possible to apply JPEG compression however this can cause unknown effects.

JPG, JPEG, JPE – Perhaps the most common file format for digital photographs, JPEG offers a relatively small file size thanks to its lossy compression system. Joint Photographic Experts Group is only the way in which the images is tranformed into data. Another extension used by JPEG is JFIF. JFIF or JPEG File Interchange Format is the actually image compressed and is what makes up most JPEG images. JPG is actually the most common file extension, but is exactly the same as its longer counterpart. This format does not perform well for line graphics or charts, but rather photographs where the compression blends in with the textures.

PSB – The Large Document Format for Photoshop is designed for images with dimensions greater than 30,000 pixels in both dimensions and up to the maximum 300,000 pixels in either dimension. This is a native Photoshop format is not supported by many (if any) other programs. The large document format is also one of several formats that allows 48-bit images (3 16-bit channels instead of 8-bit). PSB files support a majority of the PSD features and are essesntially the same except with support for large files.

PCX – PCX files were developed by ZSOFT for their PC Paintbrush software (popular DOS image editor of the time). PCX files use a color palette similar to GIF’s but support was added later for 24-bit color. PCX uses a fast but inefficient compression system. PCX files are a variation of RLE encoded bitmaps, but are very rare and serve little purpose in comparison to PNG and GIF images.

PDF, PDP – A Photoshop PDF, or Portable Document Format, is a specialized PDF designed by Adobe for Photoshop. Similar to both Acrobat PDF’s and Photoshop PSD’s, this format supports many of the features of both programs: transparency, layers and vector graphics. Photoshop PDF’s primarily use the CMYK color scheme. It is used by Adobe’s InDesign and being a PDF, it is viewable in Acrobat. This format features the security of locking the file from editing. PDP is the default file format for Broderbund’s Printshop Deluxe and is supported in Photoshop to some extent.

RAW – The Photoshop Raw format is a plugin for Photoshop enabling support for various camera’s raw image type. This allows greater control over the quality of the image. The problem with this format is its lack of support by many programs. This is caused by the fact that the image is not processed at all (or ‘not cooked’). The information captured by the camera’s sensor is exactly what makes up this file. Support for this format is growing, but the exact format varies between manufacturers. DNG is another popular raw format which is literally a digital negative of the image.

PICT – PICT files are an original image file for the Macintosh. Both vector graphics and bitmaps are supported in this format. PICT files originated as the default file format for for Quickdraw and only supported 8 black and white colors. This format evolved to support color and then higher color depths up to 32-bit. RLE and JPEG compression can be applied to PICT images with certain limits. For example, JPEG compression requires the Quicktime compressor. This format was replaced by Apple with the PDF file. It is widely supported on all the Mac operating systems, so Photoshop still keeps it supported.

PXR – The Pixar File Format is very rare ans is not commonly used for web graphics. In fact, it is not compatible with most applications or any web browsers. It is mainly used as a format for high quality 3d renders or detailed animations. PXR files do not support any type of compression and are limited mainly by their lack of support by common software.

PNG – Portable Network Graphics is a format designed to replace the GIF using superior technology. It has support for many of the GIF features including transparency. It has surp***ed the GIF in many areas, the most common being color depth and transparency. The color depth of a PNG is extended up to 48-bit and the transparency uses a much broader range of options in order to bring about the required results. PNG images are usually large files because of the higher quality they have compared to either GIF or JPG. This is due to the lossless compression used by PNG called deflation. This format also supports a more advanced interlacing system. Support for PNG images is slowly growing. All of the modern webbrowsers support viewing PNG’s, but the lack of animation is hindering further growth especially in regard to advertising on the web.

PBM, PGM, PPM, PNM, PFM – Portable Bitmaps are only one component of a set that collectively convert files between different platforms. This set contains Portable Bitmaps (PBM), Portable Graymaps PGM), Portable Pixmaps (PPM) and the whole collection is known as PNM. PBM’s are monotone and use a color depth of 1-bit. This progresses to 8-bit with PGM and then to 24-bit with PPM. Portable Bitmaps were adapted to support multiple images in each file and are now supported by several big-name programs. The PFM format was used by old printers to provide a way to process text.

SCT – Scitech Continuous Tone images are another very high quality image format used primarily by professionals in the print ad business. Designed for use with photographs and other detailed images, Scitech images use a very high color depth and the CMYK mode to produce outstanding image quality, but also very large files. SCT files take advantange of a raster system that uses color separations. This file type is limited by its exclusivity to Scitech systems, but for those that use it, the image quality and features are necessary.

TIF, TIFF – Tagged Image File Format is a common high quality image file used mainly by photographs and detailed designs. Supported by almost all major image editors, TIFF is a flexible format that can be used in cameras, scanning, printing, and design. Programs like PageMaker take advantage of TIFF images and can make the most of their features. TIFF offers the ability to archive and store JPEG’s, bitmaps and vector graphics. This format supports compression in a lossless format and images can even be edited and resaved without any loss in quality.