File Formats

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When saving your file, use the format which will best serve what you need to do.

Some formats will alter your pixels during a conversion while others compress your image to save space. These are refered to as "lossy" formats because once you save image it will never be quite the same. Others formats leave your information intact so are refered to as "non-lossy". Other file formats are compatible with other image modes, programs or even other computer platforms. To keep it all straight, here's a quick overview of the different formats and their pros and cons:

.PSD - Photoshop's native file format. This is a very reliable format specific to Photoshop. It's not very small in terms of file space (offering only a RLE1 compression scheme) but it's main advantage is that it will save all Photoshop information in your file intact. This means all your custom layers, layer masks, lettering, layer styles, groups, etc. can be saved. Unfortunately, .PSD files aren't very compatible with other graphics programs outside of the Adobe suite. It should, however, be your first choice if you want to save all your work with its elements in an editable fashion. Note: to increase compatibility with older versions of Photoshop, be sure to edit your preferences [edit>preferences>file handling>always maximize compatibility with photoshop (psd) files]. [non-lossy] [cross-platform]

.BMP - Windows Bitmap File Format. An older, but still commonly used format. Modest compression, but not recommended for comic work. [non-lossy][somewhat cross-platform]

.GIF - (Compuserve .GIF format) Acronym for Graphics Interchange Format. Unsuitable for most comic work. Modest compression, but extremely lossy on 24-bit images. Format retains only 256 colors and can introduce massive dithering. GIF89 does support tansparencies, making it useful for the net. [lossy][cross-platform]

.EPS - (Photoshop EPS) Acronym for Encapsulated PostScript. .EPS files can be used to define both raster and vector data. .EPS files defining vector data can be scaled up or down without losing detail. .EPS is an excellent format for bringing information into Photoshop, especially vector objects such as fonts, graphic elements, logos or sound effects. .EPS objects imported into Photoshop can be converted into bitmaps at any size or resolution you choose. This format is only marginally useful for saving information from Photoshop though, since most bitmap data -by its nature-does not scale well. While vector data is very small, bitmap .EPS files can get quite large. .EPS format can be useful for exporting images to programs when other formats fail. The format is also cross-platform. Photoshop DCS (desktop color separations) are also .EPS formatted files which allow you to save CMYK data and spot colors. DCS is useful in some instances for Duo-tone color and other specialized printing chores. [non-lossy/ lossy (if JPEG compression is chosen][cross-platform]

.JPEG - (aka .JPG) Acronym for Joint Photographic Experts Group. One of the most popular formats for the web. Using a series of encoders, .JPG format compresses images in 8x8 grids, averaging detail and color information. Depending on the level of compression, visual artifacting can be severe, making it generally unsuitable for comic work. The format is extremely useful for the internet because of its extreme compression capabilities and relatively decent visual quality. If you plan on editing or re-using your image, avoid this format as the compression scheme tosses large amounts of data from your image. Also, be very careful about resaving .JPG files, as this will cause them to be compressed again, further degrading their quality. [lossy][cross-platform]

.PCX - PC Paintbrush File Format. An old PC standard, revised to work with 24bit images. Widely supported on the PC, but not as much on the Mac. Not generally suitable for comic work as file sizes are larger than other formats and its compression algorithms are inefficient (an RLE scheme) leading to possible substituted image palettes. [non-lossy][possibly cross-platform]

.PDF - {Photoshop .PDF) Acronym for Portable Document Format. An Adobe file format which allows you to save graphics which can be used in Adobe Acrobat. Photoshop .PDF format can be useful for storing transparency and vector data intact for use in other Adobe products such as Indesign. While not commonly used, it is a powerful format when used in conjunction with other software. Using this format can also allow you to lock your images, preventing them from being viewed by unauthorized users. This is also one of very few formats which supports CMYK. [non-lossy/lossy (if compression is chosen)][cross-platform]

.PCT - (PICT) An Apple file format, used mostly on Macs. Widely supported by Macintosh software. Suitable for some comic applications, but not as advantageous as other formats in terms of size and compatibility. The format offers native non-lossy RLE compression for identical pixels, so images with a predominant color or large flat area will compress well. [non-lossy/lossy (if JPEG compression is chosen)][somewhat cross-platform.

.PXR - (Pixar) The Pixar Computer image format. Suitable for some comic applications, but with limitations. Supports 16 and 24-bit color, but not alpha channels or CMYK. The image files are uncompressed, so can become very large. Not recommended except for transferring file to and from Pixar computers.

.PNG - Acronym for Portable Graphics Network. Designed as a royalty-free format to .GIF. Not generally suitable for comic work, this format is better for the web. It supports 8 and 16-bit channels, spot colors, alpha channels and lossless compression. Many consider this to be the possible successor format of .JPG for web use. It also supports CRC data integrity checking and internal gamma correction. Sadly, it does not support CMYK. [non-lossy][cross-platform]

.RAW - An unencoded image dump format. This format literally dumps your pixel data straight into a file. It supports any Photoshop mode, including spot colors,16-bit channels and alpha masks. While it can be used for comic work, it's not suggested as the files are uncompressed and can be extremely large. This format can be handy for porting documents to other platforms or developmental work. [non-lossy][cross-platform]

.SCT (aka Scitex CT) Scitex Continuous Tone image file format. Designed for the Scitex image-processing devices. Not really suitable for comic work, though the format does support CMYK. Alpha channels are not supported and the format is uncompressed, making for some large files.

.TGA (aka Targa) Developed by a company known as Truevision, this format was popular on the PC. The format isn't well-suited for comic work, but can be used for some tasks. It supports 1 alpha channel but not CMYK. The format supports RLE non-lossy compression, so images with large areas of identical color will see substantial space savings.

.TIF (aka TIFF) An Acronym for Tagged Information File Format. A legacy file format originally developed by Aldus. .TIF files are well-suited for printing and is commonly used in comics. The format supports unlimited channels (both 8 and 16-bit) and CMYK mode. Images compress well with a non-lossy .LZW compression scheme2 . Mac or PC byte order generally doesn't make a difference since nearly all programs what can import/export .TIF files understand both. [non-lossy][cross-platform]

lossy compression scheme in which identical pixels next to each other can be compressed, resulting in a smaller file. This method of compression works very well for large areas offlat color, but results in almost no savings if the image is photographic or grainy.

2 LZW - An acronym for Lempel, Ziv and Welch, the programmers who created the compression algorithm. LZW compression works by substituting common values in data with a shorthand notation, so redundant information can be replicated, not stored in its entirety. Tifs compressed with this method take longer to save and open since they must be compressed and decompressed.

In images with lots of redundant data, the compression can be enormous. If the image is grainy, the savings will only be slight. ■

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