EPSFEPSF is a special structuring convention for Adobe PostScript files. This convention allows you to embed EPSF graphics into other PostScript documents.
Some Macintosh programs can accept EPSF documents and render them onto a PostScript printer.
GIFConverter does not support EPSF. Reading EPSF files requires a PostScript interpreter, which is usually found in printers, or, rarely, on a computer. GIFConverter does not contain a PostScript interpreter.
GIFConverter creates EPSF documents in two modes. The normal mode has a file type of EPSF, and contains a picture that other programs use when showing the EPSF graphic on the screen.
If you choose text only , the file has a type of TEXT and contains only the PostScript code. This form is ideal for hand editing files or sending the EPSF file to some other type of computer.
GIFConverter places images into the EPSF file as separate objects according to the following table.
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Display
Mode
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Output
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|
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Cyan,
Magenta, Yellow, or Black
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Halftone
image containing separation at appropriate screen angle.
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|
|
Grayscale,
Color
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Halftone
image of the gray components.
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|
Turning on Save as Text causes the EPSF output to be saved to a text file for easier editing.
GIFConverter does not support the colorimage operator. EPSF documents created in Color mode contain a grayscale image only.
GIFGIF is the Graphics Interchange Format, designed by CompuServe to meet its needs for a machine-independent file format.
GIF files can contain one or more images, each containing 256 colors of a possible 16,777,216 colors, as well as a colored background. Each image is compressed using LZW [2] compression, which can reduce the size of the stored image by 30-50% or more.
GIFConverter fully supports the GIF87a standard.
GIFConverter reads the background color. It reads each image in the GIF file into a separate image in memory. You can edit or move each image in a GIF file individually.
If the Global maps in multi-image GIF files option is turned on, GIFConverter writes GIF files with a global color map that encompasses the best compromise colors to use for all the images and the background color. The global color map helps programs to determine which colors are the best to display before reading the rest of the GIF file. Each image has a local color map indicating the precise colors used in that image.
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Display
Mode
|
Output
|
|
|
Cyan,
Magenta, Yellow, or Black
|
GIFConverter
writes separate images containing the separation in its proper color.
|
|
|
Grayscale
|
GIFConverter
writes separate images containing grayscale information.
|
|
|
Color
|
GIFConverter
writes separate images containing full color information.
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|
Turning on the Save Interlaced option causes GIFConverter to store GIF files in “interlaced” format, which allows online viewers to see some of the image progressively as it arrives over the modem. When you check this option, GIFConverter saves every eighth scan line, then every fourth between them, then the remaining lines are filled in. This option is for uploading files intended to be viewed online.
Turning on Global maps causes GIFConverter to write a “global color map” when there is more than one image. This global map contains summary information about the colors in all the images. Each image still contains a list of colors that it uses. This box is initially unchecked since some GIF decoders mishandle files that contain both global and local color maps. If you have GIF files with more than one image, and other programs display them improperly, try changing this setting.
If the 87a Compatibility checkbox is turned on (which it is when you first start GIFConverter), GIFConverter will warn you if you save GIF files that contain any extensions that require the 89a specification, like the text comments. If you want to use comment text, turn off the 87a Compatibility checkbox.
GIFConverter writes eight bit GIF images even when in One Bit mode. This allows you to save GIF files with grayscale or color images on black-and-white Macintoshes.
JPEG/JFIFThe Joint Photographic Experts Group developed the JPEG compression scheme to support the digitizing and compression of photographs. The compression scheme is “lossy,” that is, it sacrifices some information to achieve up to 20:1 compression. The theory behind JPEG is that there is no need to store information that the eye can’t see anyway. The color of small details and some of the small details themselves are removed before compression.
Even as a lossy compression algorithm, JPEG’s capability to store full-color (24-bit) images in small files makes it attractive for electronically handling photographs. A JPEG-compressed photograph exhibits none of the graininess seen in photographs compressed with a 256-color scheme such as GIF.
The JFIF format is one of many formats intended for storing JPEG files. JPEG-compressed graphics may also be encapsulated in PICT files.
GIFConverter can read and write JFIF files with 256 greys or millions of colors.
If you check the Use QuickTime box, GIFConverter uses an available QuickTime compressor. This box is only available if QuickTime is present.
Checking the Progressive box yields a progressive JPEG that draws into the screen gradually.
The Image Quality may be varied from 0 to 100; 75 is a good default. Settings towards 0 may cause increasing image degredation.
Decompressing and recompressing JPEG graphics many times can cause noticeable changes in the images.
MacPaintMacPaint is a one-bit raster format initially designed by Apple Computer, Inc. It contains a single image of 576 x 720 pixels.
GIFConverter reads MacPaint documents into a document containing a single image. If you set the Auto Crop on Open option (see the Options... command above), GIFConverter automatically crops the image to the smallest portion that contains black pixels. This saves memory, and eliminates unnecessary white space automatically.
On output, the upper left 576 x 720 pixels of the document are written into a MacPaint file.
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Display
Mode
|
One
Bit Output
|
Eight
Bit Output
|
|
Cyan,
Magenta, Yellow, or Black
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Dithered
bitmap containing a single separation.
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Not
recommended.
|
|
Grayscale
|
Dithered
grayscale bitmap.
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Not
recommended.
|
|
Color
|
Not
recommended.
|
Not
recommended.
|
Turning on the Auto Crop on Open option will cause GIFConverter to crop all paint files to the smallest non-white area they contain when opened. This can help when manipulating paint files under memory constraints.
In both Eight Bit and One Bit Color modes, the output files will contain blobs of black, since anything not white writes as black.
If the document is larger than 576 x 720 pixels, only the upper left portion will be written to the Paint file.
PICTThe Macintosh uses this format in PICT files, on the clipboard, and in the StartupScreen files (see below). Most Macintosh graphic programs can read and write PICT files. The conventions listed here for PICT input and output apply to all three uses.
The PICT 2 format is an extension of PICT for Color QuickDraw. It can handle a virtually unlimited number of colors. This version of PICT works best on Macintosh II series and SE/30 CPUs. Other Macintosh CPUs can interpret PICT 2 files, but with a loss of all color information: all colors that are not white appear as black.
The original PICT format supports eight colors: red, green, blue, cyan, magenta, yellow, black, and white. Although all colors except white appear black on the screen, the ImageWriter II printer driver interprets these colors properly for printing.
When reading an original PICT, or on a CPU that does not have Color QuickDraw, GIFConverter reads the eight colors available in the original PICT format.
When reading a PICT 2 document on a CPU that does have Color QuickDraw, GIFConverter first scans the picture looking for all the colors that it contains. If there are more than 256 colors, GIFConverter chooses 256 compromise colors for the document. [3] The colors are used to make the color map. GIFConverter then re-reads the picture, mapping each color in the picture to the closest color it has chosen for the document.
On output, GIFConverter simply draws the contents of the screen into the PICT file.
If the Eight Bit option is chosen, GIFConverter writes a color PICT 2 picture. It also adds some color table information required by early Macintosh II programs. [4]
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Display
Mode
|
One
Bit Output
|
Eight
Bit Output
|
|
Cyan,
Magenta, Yellow, or Black
|
||
|
Grayscale
|
||
|
Color
|
PICT files can be compressed if QuickTime is installed. Click on the Compression... button to adjust the compression options.
Checking the Include Color Resources button includes several color resources that early color painting programs made use of.
PNGPNG is the Portable Network Graphics format, a lossless graphic format that offers from one-bit (black and white) images up to 16 bit greyscale and 48 bit color images. PNG was developed in response to the patent threats to the GIF graphics format.
GIFConverter can or write read PNG files with up to millions of colors; it only supports 8 bits per sample.
Interlaced causes PNGs to show up a bit at a time, the same way as GIFs do, except that PNG files interlacein both directions.
The Compression Level is a trade off between speed, memory, and time. The default of 6 is pretty good.
Filtering can improve compression. There are four filters, Sub, Up, Average, and Paeth. The Automatic setting is usually the best, because it tries to choose the filters that give the best compression automatically.
RIFFRIFF, or Raster Image File Format, is a format designed by Mark Zimmer of Fractal Software. A RIFF file contains a single image of up to 256 grays or colors.
GIFConverter reads the RIFF file as single image in a new document.
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Display
Mode
|
Output
|
|
|
Cyan,
Magenta, Yellow, or Black
|
Grayscale
document containing the chosen color separation.
|
|
|
Grayscale
|
Up
to 256 grays.
|
|
|
Color
|
Up
to 256 colors. If the images contain more than 256 colors, the best 256 colors
are used.
|
|
There are no options for RIFF except for choosing the number of colors in the output image.
GIFConverter only supports the grayscale and “virtual lookup table” (color table based) variants of RIFF. It does not support 24-bit RGB, HSL, CMY, and CMYK separation files.
RLEThe RLE (or Run-Length Encoded) format is an early format used on CompuServe. GIFConverter provides this format for compatibility with small machines that do not have enough memory to read GIF files.
RLE files contain a single image, either 128 x 96 or 256 x 192 pixels.
GIFConverter reads the file into a single image.
GIFConverter chooses the smallest size that will still enclose the document. If the document is larger than 256 x 192 pixels, then GIFConverter only saves the upper-leftmost area.
GIFConverter saves an RLE file as if it were a small MacPaint file. See that section for details on the way images are saved.
Scan ImageThe Thunderscan and Thunderworks programs use the Scan Image format to store scanned images. It stores a single image with up to 32 gray levels.
GIFConverter reads the file into a single image.
GIFConverter creates a single image containing what you see in a window. This image is written to the Scan Image file according to the following restrictions:
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Display
Mode
|
Output
|
|
|
Cyan,
Magenta, Yellow, or Black
|
||
|
Grayscale,
Color
|
||
Scan Image files contain grayscale data even if One Bit mode is chosen. This allows you to save Scan Image files with grayscale information on black-and-white Macintoshes.
Slide ShowThe Slide Show format is not a graphics format, but a special file type where GIFConverter keeps references to other files. You can create a Slide Show file by using then New Slide Show... command in the File menu.
Startup ScreenThe Startup Screen format derives its name from the StartupScreen file placed in the System Folder and displayed when the Macintosh boots. The original StartupScreen file contained a single one-bit image of 512 x 342 pixels to match the size of the original Macintosh screen. On Macintoshes with Color QuickDraw, the file contains a single PICT (or PICT 2) that the Macintosh draws on the screen, adding color and the ability to cover larger screens.
GIFConverter can read and write both kinds of Startup Screen.
When reading a Startup Screen file, GIFConverter follows the following rules:
If there is a PICT in the file, and GIFConverter is running on a Macintosh with Color QuickDraw, read the PICT.
If there is an original-format StartupScreen in the file, and GIFConverter is running on a Macintosh without Color QuickDraw, read the original-format StartupScreen.
Otherwise, read whatever is in the file.
See also the discussion of the PICT format above.
GIFConverter writes the StartupScreen file according to the settings in the Options... dialog box (see above).
Writing a PICT-style Startup Screen works like the PICT file, above.
Writing an original-format Startup Screen works like the MacPaint format, except that GIFConverter restricts the image size to 512 x 342 pixels. See the MacPaint format for more information.
There are two kinds of Startup Screens. The original Startup Screen was a black-and-white image. Macintosh II computers can read a Startup Screen that contains a color picture.
Clicking the Mac II format option will cause GIFConverter to place a color picture into the StartupScreen file. Color Macintoshes (Macintosh II series, Macintosh Quadra series, and the Macintosh SE/30) read this data to produce the color picture on the screen.
Clicking the Original format option will cause GIFConverter to create an original-style black-and-white Startup Screen. Macintoshes without Color QuickDraw use this data to produce the image on the screen.
If you read a PICT style Startup Screen on a Macintosh without Color QuickDraw, the results are usually rather poor. The picture may be blotchy.
TIFFTIFF, or Tag Image File Format, is a format developed by Aldus Corporation and Microsoft Corporation for storing images.
GIFConverter fully supports TIFF classes G, P, and R of the version 5.0 specification. GIFConverter supports LZW compression for input only. The TIFF classes are:
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Class
|
Description
|
|
B
|
Black-and-white
images. Compression options include CCITT 1D or PackBits. GIFConverter supports
only uncompressed class B.
|
|
G
|
Grayscale
data, 4 or 8 bits per pixel.
|
|
P
|
Palette
color, up to 256 colors, one to eight bits per pixel.
|
|
R
|
RGB
full color; 16,277,216 possible colors.
|
GIFConverter reads the image into a new document.
GIFConverter creates a single image containing what you see on the screen, and writes the image to the file according to the following table:
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Display
Mode
|
Output
|
|
|
Cyan,
Magenta, Yellow, or Black
|
TIFF
Class G file containing the grayscale data corresponding to the desired
separation.
|
|
|
Grayscale
|
TIFF
Class G file containing grayscale data.
|
|
|
Color
|
TIFF
Class P file containing palette color data. If there are more than 256 colors
among the images, the best 256 are chosen, and the images are written using the
closest colors in the palette.
|
|
Turning on Compression causes TIFF files to be saved with LZW compression. Clicking on Use Prediction can improve the compression, but may not be compatible with some other applications.
The MS-word Fix checkbox causes GIFConverter to allow for errors in the TIFF file support in Microsoft Word and other Microsoft products.
GIFConverter’s support of Class G implies support of class B without compression (a grayscale image with only two colors is the same as a black and white image).
GIFConverter does not support privately defined compression schemes. These schemes are legal in TIFF, but not recommended under version 5.0 of TIFF.
[2]Lempel-Ziv-Welch
[3]For technical readers, GIFConverter uses the Median Cut Algorithm in this case.
[4]To be technical, it puts ‘COLR’, ‘ctab’, and ‘pltt’ resources into the resource fork.
Copyright ©1998 by Kevin A. Mitchell. All rights reserved.