- pixels
- raster images
- vector images
- bit or colour depth
- colour space
- image capturing
- optimising
Information from the Internet: Pixels
"Pixels in digital imaging, a pixel (picture element or picture cell) is the smallest addressable screen element in raster graphics; it is the smallest unit of picture that can be controlled. Each pixel has its own address. The address of a pixel corresponds to its coordinates. Pixels are normally arranged in a two-dimensional grid, and are often represented using dots or squares. Each pixel is a sample of an original image; more samples typically provide more accurate representations of the original. The intensity of each pixel is variable. In color image systems, a color is typically represented by three or four component intensities such as red, green, and blue, or cyan, magenta, yellow, and black."
Information from the Internet: Raster Images
A bitmap corresponds bit-for-bit with an image displayed on a screen, generally in the same format used for storage in the display's video memory, or maybe as a device-independent bitmap. A bitmap is technically characterized by the width and height of the image in pixels and by the number of bits per pixel (a color depth, which determines the number of colors it can represent)."
"Vector graphics is the use of geometrical primitives such as points, lines, curves, and shapes or polygon(s), which are all based on mathematical equations, to represent images in computer graphics.
Vector graphics formats are complementary to raster graphics, which is the representation of images as an array of pixels, as is typically used for the representation of photographic images. There are instances when working with vector tools and formats is the best practice, and instances when working with raster tools and formats is the best practice. There are times when both formats come together. An understanding of the advantages and limitations of each technology and the relationship between them is most likely to result in efficient and effective use of tools."
Information from the Internet: Bit or Colour Depth
"As the number of bits increases, the number of possible colors becomes impractically large for a color map. So in higher color depths, the color value typically directly encodes relative brightnesses of red, green, and blue to specify a color in the RGB color model.
8-bit direct color
A very limited but true direct color system, there are 3 bits (8 possible levels) for each of the R and G components, and the two remaining bits in the byte pixel to the B component (four levels), enabling 256 (8 × 8 × 4) different colors. The normal human eye is less sensitive to the blue component than to the red or green,[citation needed] so it is assigned one bit less than the others. Used, amongst others, in the MSX2 system series of computers in the early to mid 1990s.
Do not confuse with an indexed color depth of 8bpp (although it can be simulated in such systems by selecting the adequate table).
16-bit direct color
In 16-bit direct color, there can 4 bits (16 possible levels) for each of the R, G, and B components, plus optionally 4 bits for alpha (transparency), enabling 4,096 (16 × 16 × 16) different colors with 16 levels of transparency. Or in some systems there can be 5 bits per color component and 1 bit of alpha (32768 colors, just fully transparent or not); or there can be 5 bits for red, 6 bits for green, and 5 bits for blue, for 65536 colors with no transparency. These color depths are sometimes used in small devices with a color display, such as mobile telephones.
Variants with 5 or more bits per color component are sometimes called high color,which is sometimes considered sufficient to display photographic images."
Information from the Internet: Colour Space
"A color model is an abstract mathematical model describing the way colors can be represented as tuples of numbers, typically as three or four values or color components (e.g. RGB and CMYK are color models). However, a color model with no associated mapping function to an absolute color space is a more or less arbitrary color system with no connection to any globally-understood system of color interpretation.
Adding a certain mapping function between the color model and a certain reference color space results in a definite "footprint" within the reference color space. This "footprint" is known as a gamut, and, in combination with the color model, defines a new color space. For example, Adobe RGB and sRGB are two different absolute color spaces, both based on the RGB model."
"A wide range of colors can be created by the primary colors of pigment (cyan (C), magenta (M), yellow (Y), and black (K)). Those colors then define a specific color space. To create a three-dimensional representation of a color space, we can assign the amount of magenta color to the representation's X axis, the amount of cyan to its Y axis, and the amount of yellow to its Z axis. The resulting 3-D space provides a unique position for every possible color that can be created by combining those three pigments."
"A Bayer filter mosaic is a color filter array (CFA) for arranging RGB color filters on a square grid of photosensors. Its particular arrangement of color filters is used in most single-chip digital image sensors used in digital cameras, camcorders, and scanners to create a color image. The filter pattern is 50% green, 25% red and 25% blue, hence is also called RGBG, GRGB, or RGGB."
"The Bayer filter is almost universal on consumer digital cameras. Alternatives include the CYGM filter (cyan, yellow, green, magenta) and RGBE filter (red, green, blue, emerald), which require similar demosaicing. The Foveon X3 sensor (which layers red, green, and blue sensors vertically rather than using a mosaic) and arrangements of three separate CCDs (one for each color) don't need demosaicing."
Information from the Internet: Optimising
"Optimising images for the web is a tricky business. You have to get the right balance between filesize and picture quality. It is an essential step though. Look at any webpage, and you will see that most of its load time comes from images. Your website will be needlessly slow if you don't drop the sizes of these images.
There are three key areas where bytes can be shaved off your graphics: bit depth (number of colours), resolution, and dimension. Here I'm going to show you the practicalities of web graphics optimisation, and less of the technicalities. You don't need expensive graphics editors to compress the sizes of your images, as there are plenty of free utilities and shareware that will do the job for you."
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