indexed color

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indexed color

A method of compressing an image that enables 8 bits per pixel to look almost as good as 24 bits per pixel. The technique determines the 256 most frequently used colors in the image and creates a color lookup table, also called a "color map" or "color palette," that is stored with the image. Rather than each pixel in the image having all three RGB colors (one 8-bit red, one 8-bit green and one 8-bit blue), each pixel contains one 8-bit number that indexes into the 256-color lookup table, which contains the RGB values (see illustration below).

It Used to Be a Major Problem
When early computer screens were commonly limited to 256 colors, indexed color methods were essential. Even then, two indexed photos on screen at the same time with vastly different color schemes would overload the hardware's color capacity and cause images to display improperly. Today, computer hardware easily renders full 24-bit color, but 8-bit indexed images are still widely used to save bandwidth and storage space. See color depth, color palette and color lookup table.


Color Palette Index
The pixels in the image contain index numbers that point to the RGB value in the color lookup table. The RGB values are the ones used by the display system.







24-Bit vs. 8-Bit
Indexed color images can look nearly identical to their 24-bit originals, because the 256 most frequently used colors are identified. The 256-color palette (top) was created in Photoshop from the original 24-bit image (left) to generate the image as 8 bits (right).


24-Bit vs. 8-Bit
Indexed color images can look nearly identical to their 24-bit originals, because the 256 most frequently used colors are identified. The 256-color palette (top) was created in Photoshop from the original 24-bit image (left) to generate the image as 8 bits (right).
References in periodicals archive ?
The index that is designed as a trip in the subway allows readers to read the book in three different ways: linear (from beginning to end), by the routes indicated by the writer on the index map (in the style of Cortazar and his Rayuelo), or in the order that the reader wishes.
Check that the pet shop chain actually does own the land by conducting an index map search at the Land Registry.
Volume 2 contains the index map and 22 maps on the recommended constituency boundaries and the related boundary descriptions.
The concavity index map (CIM) revels that streams near Bunji and Astore regions of the study area are flowing with relatively low gradient with (low concavity index) and have intermittent profiles mostly affected by erosion in their vicinity which are clear signs of relatively older surface.
Corruption Perception Index Map (image courtesy of Transparency International)
In the previous version of SuperGIS Web Mapper, web administrators can simply switch on or off to determine if visitors have access to each tool, like Identify, Index Map, Query, Measure, Print, Draw Tool, Basemap, etc.
After the official search, the landowner, with the help of the surveyor, is required to get a registry index map (RIM) from the Survey of Kenya.
When total index map of all periods were examined, it was seen that the intensity generally contains Eastern Anatolia Region of the country.
Index map search An index map search should be made where the property is unregistered or includes unregistered land, or where the property is being sold by reference to a contract plan that is not the title plan and so may include unregistered land or land comprised in more than one registered title.
WATER QUALITY INDEX MAP Bhikanpur Charauri Pasaunda Nandgram Surana Khindora LEGEND Water quality index 80.0 Newari Mawi Kalchhina Niddi Galand Kakrana Dhaulana NTPC Ghaziabad Dasna Sadarpur Morta Muradnagar Jabalpur Bhadoli Abidpur N An index map of part of Hindon basin in Uttar Pradesh The map shows most samples fall in very poor category having a water quality index > 20 and above.
As with any piece of land in which you are anxious to establish ownership the first step is to make an index map search of the Land Registry.