It is NOT a tutorial. Hopefully, this book is what you'll reach for when you want find out what Peter Norton or the "official" references glossed over. This manual is intended to replace the various expensive references needed to program for the DOS environment, that stack of magazines threatening to take over your work area, and those odd tables and charts you can never find when you need them. The various Microsoft and IBM publications and references don't always have the same information.
History[ edit ] CompuServe introduced GIF on June 15, to provide a color image format for their file downloading areas, replacing their earlier run-length encoding RLE format, which was black and white only. GIF became popular because it used LZW data compressionwhich was more efficient than the run-length encoding that formats such as those used by PCX and MacPaintand fairly large images could therefore be downloaded in a reasonably short time, even with very slow modems.
The original version of GIF was called 87a. The 89a specification also supports incorporating text labels as text not embedding them in the graphical databut as there is little control over display fonts, this feature is not widely used. CompuServe encouraged the adoption of GIF by providing downloadable conversion utilities for many computers.
The feature of storing multiple images in one file, accompanied by control data, is used extensively on the Web to produce simple animations.
The optional interlacing feature, which stores image scan lines out of order in such a fashion that even a partially downloaded image was somewhat recognizable, also helped GIF's popularity,  as a user could abort the download if it was not what was required.
The press's lexicographers voted it their word of the yearsaying that GIFs have evolved into "a tool with serious applications including research and journalism". Steve Wilhite says that the intended pronunciation deliberately echoes the American peanut butter brand Jifand CompuServe employees would often say "Choosy developers choose GIF", spoofing this brand's television commercials.
The New Oxford American Dictionary gave only "jif" in its 2nd edition  but updated it to "jif, gif" in its 3rd edition. On the occasion of receiving a lifetime achievement award at the Webby Award ceremony, Wilhite rejected the hard-"G" pronunciation,    and his speech led to 17, posts on Twitter and 50 news articles.
Usage[ edit ] GIFs are suitable for sharp-edged line art such as logos with a limited number of colors. This takes advantage of the format's lossless compression, which favors flat areas of uniform color with well defined edges. Many GIF files have a single image that fills the entire logical screen.
Others divide the logical screen into separate sub-images.
The images may also function as animation frames in an animated GIF file, but again these need not fill the entire logical screen. GIF files start with a fixed-length header "GIF87a" or "GIF89a" giving the version, followed by a fixed-length Logical Screen Descriptor giving the pixel dimensions and other characteristics of the logical screen.
The screen descriptor may also specify the presence and size of a Global Color Table, which follows next if present. Thereafter, the file is divided into segments, each introduced by a 1-byte sentinel: An image starts with a fixed-length Image Descriptor, which may specify the presence and size of a Local Color Table which follows next if present.
The image data follows: Extension blocks blocks that "extend" the 87a definition via a mechanism already defined in the 87a spec consist of the sentinel, an additional byte specifying the type of extension, and a linked list of sub-blocks with the extension data.
Extension blocks that modify an image like the Graphic Control Extension that specifies the optional animation delay time and optional transparent background color must immediately precede the segment with the image they refer to. The linked lists used by the image data and the extension blocks consist of series of sub-blocks, each sub-block beginning with a byte giving the number of subsequent data bytes in the sub-block 1 to The series of sub-blocks is terminated by an empty sub-block a 0 byte.
This structure allows the file to be parsed even if not all parts are understood. A GIF marked 87a may contain extension blocks; the intent is that a decoder can read and display the file without the features covered in extensions it does not understand. The full detail of the file format is covered in the GIF specification.
Due to the reduced number of colors in the image, there are display issues. The color definitions in the palette can be drawn from a color space of millions of shades shades, 8 bits for each primarybut the maximum number of colors a frame can use is This limitation seemed reasonable when GIF was developed because few people could afford the hardware to display more colors simultaneously.
Simple graphics, line drawings, cartoons, and grey-scale photographs typically need fewer than colors. Each frame can designate one index as a "transparent background color": Many techniques, collectively called ditheringhave been developed to approximate a wider range of colors with a small color palette by using pixels of two or more colors to approximate in-between colors.
These techniques sacrifice spatial resolution to approximate deeper color resolution. This is often not an ideal solution for GIF images, both because the loss of spatial resolution typically makes an image look fuzzy on the screen, and because the dithering patterns often interfere with the compressibility of the image data, working against GIF's main purpose.
In the early days of graphical web browsers[ when? When bit color became the norm palettes could instead be populated with the optimum colors for individual images. A small color table may suffice for small images, and keeping the color table small allows the file to be downloaded faster.
Both the 87a and 89a specifications allow color tables of 2n colors for any n from 1 through 8. Most graphics applications will read and display GIF images with any of these table sizes; but some do not support all sizes when creating images.
Tables of 2, 16, and colors are widely supported. True color[ edit ] An animated GIF illustrating a technique for displaying more than the typical limit of colors Although GIF is almost never used for true color images, it is possible to do so. Alternatively, the GIF89a specification introduced the idea of a "transparent" color where each image block can include its own palette of visible colors plus one transparent color.Numbers with Two Decimal Digits - Hundredths This is a complete lesson with instruction and exercises about numbers with two decimal digits (hundredths), meant for fourth grade.
On a number line, we get hundredths by simply dividing each interval of one-tenth into 10 new parts. When we write numbers with hundredths using decimals we use a decimal point and places to the right of this decimal point.
The hundredth place is two places to the right of the decimal point. Write each as a decimal fraction: a four units, one hundred and twenty two thousandths _____ b one hundred and eleven, and sixty five hundredths _____ or 13 tenths and 8 hundredths or 1 unit and 38 hundredths.
Decimal fractions – renaming decimals It may help to write these numbers in. Learn to read and write decimals at your own pace. hundredths: 5 x Example 4: When asked to write two hundred thousandths as a decimal, three students gave three different answers as shown below.
Which student had the correct answer? Student 1: , No prep math worksheets.
Multiplication mastery is close at hand with these thorough and fun worksheets that cover multiplication facts whole numbers, fractions, and decimals, including word problems. Multiplication workbooks help with learning math facts.
Math centers help to reinforce multiplication skills. Numbers in English - English Vocabulary for English Learners. Los números en inglés.