09 File Formats

PSD Files

PSD files (PhotoShop Document) is the default file format for newly created images—and the only format supporting all available image modes (Bitmap, Grayscale, Duotone, Indexed Color, RGB, CMYK, Lab, and Multichannel), guides, alpha channels, spot channels, and layers (including adjustment layers, type layers, and layer effects).

If you’re exporting files to an application that doesn’t support the Adobe Photoshop format, use the Save a Copy command to save a duplicate file in a format supported by that application.

Saving Adobe Photoshop files - PSD


To save a file in its current format:

  1. Choose File > Save.

To save a file in a different file format:

  1. Choose File > Save As
  2. For Save As (Windows) or Format (Mac OS), choose a format. Unavailable formats are not visible (Windows) or dimmed (Mac OS).

Important: Only the Photoshop (and TIFF) format is available for layered files. In addition, many formats do not support files in certain color modes or files with alpha channels (see About file formats). If you do not see the format you want, flatten the image or use the Save a Copy command.

To save a copy of a file:

  1. Choose File > Save a Copy.
  2. For Save As (Windows) or Format (Mac OS), choose a format.
  3. To flatten all visible layers, select Flatten Image. (See Flattening all layers.
  4. To remove alpha channels from the image, select Exclude Alpha Channels.
  5. To remove data such as paths, guides, grids, thumbnail previews, color and printing ink profiles, and file information (such as captions) from the image, select Exclude Non-Image Data. (This option may be unavailable to some formats.) Excluding non-image data can help reduce the image’s file size.
  6. Click Save.
BMP

BMP (Bitmap) is the standard Windows image format on DOS and Windows-compatible computers. The BMP format supports RGB, indexed-color, grayscale, and Bitmap color modes, and does not support alpha channels.

Note: The word bitmap is also used as a general term for an electronic picture made up of dots. A PhotoShop picture could be called a bitmap picture even though it is PSD file. You could not refer to a PhotoSHop file as a BMP - This specifically refers to the Bitmap file format.

TIFF

A TIFF file stands for Tagged Image File Format and was designed for storing black and white, grayscale, or color bitmap images. TIFF is the a universal format for all bitmap images due to it's cross-platform compatibility (Windows and Macintosh). TIFF is a flexible bitmap image format supported by virtually all paint, image-editing, and page-layout applications. Also, virtually all desktop scanners can produce TIFF images. TIFF files also tend to retain better image quality than a JPG or GIF file, especially when printing.

The TIFF format supports CMYK, RGB, grayscale, layers and alpha channels.

When you save an Adobe Photoshop image in TIFF, you can choose to save in a format that can be read either by IBM PC-compatible or Macintosh computers. To compress the file automatically, click the LZW Compression check box; compressing a TIFF file decreases its file size but increases the time required to open and save the file.

JPEG

The Joint Photographic Experts Group (JPEG) format is commonly used to display photographs and other continuous-tone images on the World Wide Web and email services. The JPEG format supports CMYK, RGB, and grayscale color modes, and does not support alpha channels. Unlike the GIF format, JPEG retains all color information in an RGB image but compresses file size by selectively discarding data.

A JPEG image is automatically decompressed when opened. A higher level of compression results in lower image quality, and a lower level of compression results in better image quality. In most cases, the Maximum quality option produces a result indistinguishable from the original.

What's wrong with using a JPG file for artwork?

Well, nothing really! It's just that JPG files have built-in compression options to make them as small as possible in file-size, usually for the internet. However, what looks good on screen, NEVER equals what is printed. And this is even more true with JPG files. They don't retain as high of an image quality, especially if compressed, which means the print will look pixelated. This typically happens when you save an image off the internet and try to print it. Most images on the internet (unless specified otherwise) are 72 ppi or screen resolution; not high enough for quality printing! If you need to use a JPG file, make sure the resolution is 300 dpi and the compression set to the highest possible quality.

GIF

The Graphics Interchange Format (GIF) is the file format commonly used to display indexed-color graphics and images in hypertext markup language (HTML) documents over the World Wide Web and other online services. GIF is a LZW-compressed format designed to minimize file size and electronic transfer time. The GIF format does not support alpha channels.

You can convert files to GIF format using one of the following methods:
  • The File > Save As command lets you save a Bitmap-mode, grayscale, or indexed-color image in GIF format and specify an interlaced display. An interlaced image appears gradually in increasing detail as it is downloaded from the Web but can increase the file size. You cannot save alpha channels with the image.
  • The GIF89a Export command lets you convert an RGB or indexed-color image to GIF89a format, specify interlacing, and define background transparency. (See Exporting images.) The GIF89a format supports single alpha channels.

PNG

Developed as a patent-free alternative to GIF, the Portable Network Graphics (PNG) format is used for 'losslessly' compressing and displaying images on the World Wide Web. Unlike GIF, PNG supports 24-bit images and produces background transparency without jagged edges; however, some older versions of Web browsers may not support PNG images. The PNG format supports grayscale and RGB color modes with a single alpha channel, and Bitmap and indexed-color modes without alpha channels. PNG uses the saved alpha channel to define transparency in the file; be sure to delete all but the desired alpha channel from your image before saving as PNG.

When saving in PNG format, you can select Adam7 to display the image in increasing detail as it is downloaded. You can also run the image through a filtering algorithm that prepares the image data for optimal compression:

What is an EPS file?

An EPS file stands for Encapsulated PostScript File and was designed to store vector graphics created in programs such as Adobe Illustrator or Macromedia Freehand. EPS files can also store bitmap images, but it is not recommended because they are less efficient than a TIFF file and could result in longer print times and other possible errors. The format is compatible on both Windows and Macintosh platforms. Basically, if you have a vector art image, save it as an EPS file. If you have a bitmap image, save it as a TIFF file. Because EPS files are fairly complex, you will probably get a bewildering dialogue box when saving them! Don't worry, just use the provided default settings and everything should work.

The EPS format supports Lab, CMYK, RGB, indexed-color, duotone, grayscale, and Bitmap color modes, and does not support alpha channels. EPS does support clipping paths.

Photoshop EPS

The Encapsulated PostScript (EPS) language file format can contain both vector and bitmap graphics and is supported by virtually all graphic, illustration, and page-layout programs. The EPS format is used to transfer PostScript language artwork between applications. When you open an EPS file containing vector graphics created in another application, Photoshop rasterizes the file, converting the vector graphics to pixels.

 

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