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 ?
We have increased the file size limit for any supporting plans that customers attach to online applications for a Search of the Index Map (SIM), or Official Search of Part of the Land in a Registered Title (with Priority) (OS2).
The latest addition to the solution is the PurePixel Chlorophyll Index map and enhanced cloud and shadow detection algorithms.
Index map search An index map search should always 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.
Ms Burt spoke out after inspecting an index map of UV rays at a special molewatch clinic set up by Cancer Research UK this week at Westminster.
Part of the funds will be used to hire consultants for a Parcel Index Map Project.
However, the absence of an index map for the MRPI sheets made it extremely difficult to assess the completeness, and thus the accuracy, of its data.
Tenders are invited for Similar type of survey works and having sound financial status Preparation of index map for boundary demarcation of land for JVC at PTPS Patratu with following scope of work.
Index map search AN index map search should be made where the property is unregistered or includes unregistered land.
While Chad and the Central African Republic are included, they are not shown on the general coverage map on the back cover, whereas Cape Verde is not included, despite being indicated as included on the index map inside the back cover.
Tenders are invited for Execution of BAIS RIVER DIVERSION PROJECT from Udayagiri Stop Dam near village Udayagiri Tehsil Vidisha District Vidisha to Betwa River in Vidisha City as shown in Index Map on Turn Key basis by constructing an underground Pipe Diversion Channel System capable of delivering
Beginning with an index map and the legend, the maps are arranged in a generally anti-clockwise direction from European Turkey through Arabia, Iran, the Caucasus, northern Turkey, and finally Cyprus.
Tenders are invited for Preparation & Submission of hard copy & soft copy (editable) of Index Map within Jurisdiction of Mahananda Barrage Circle with