Image/Color Basics What is a Bit? Smallest unit of information on a machine (On/Off: 1/0) What is Bit Depth? Bit depth specifies how much color information is available for each pixel in an image. The more bits of information per pixel, the more available colors and more accurate color representation. 1- bit depth image has pixels with two possible values: black and white. monochrome 8-bit depth image has 256 possible values between Black and White: (2 to the 8th) Grayscale 0 or 1 0 or 1 0 or 1 0 or 1 0 or 1 0 or 1 0 or 1 0 or 1 1 bit 2 bit 3 bit 4 bit 5 bit 6 bit 7 bit 8 bit -- Binary Language to describe numbers from 0-256. 24- bit image has 8‑ bits per channel (bpc) RGB. (8 bits x 3 channels = 24 bits of data for each pixel). which means it has over 16 million possible color values. 32- bit: RGBA Alpha Higher Bits Per Channel: HDR (High Dynamic Range) 36-bit and higher: Photoshop can also work with images that contain 16‑ bpc (bit per channel) or 32‑ bpc. The intention of HDR is to accurately represent the wide range of intensity levels found in real scenes ranging from direct sunlight to shadows. What is a Byte? There are 8 Bits in a Byte Byte: unit of information storage Kilobyte; 1000 bytes Megabyte: 1 million Gigabyte: 1 billion Tereabyte: 1 trillion Petabyte: a very big number Hertz: Base unit of frequency Kilohertz Megahertz Gigahertz: 1 billion cycles per second being processed by the processor Terahertz Compression Types of formats that use it: o Image o Video o Audio Types of compression o Lossy Data/image loss Smaller file Great for delivering post-production o Lossless No data/image loss Larger file Great for transferring files pre-production The higher the compression, the lower the image quality. Color Space/Model/Modes: Color Model: Numberic method for describing color. (RGB, CMYK, HSB) Color Space: a variant of a color model with a specific gamut or colors. (Adobe RGB, sRGB, PrpPhoto RGB). Each device has it’s own colors space. - color profile - color management Color Mode: determines the number of colors and channels in an image. This affects the file size and file format available. RGB uses additive color mixing, because it describes what kind of light needs to be emitted to produce a given color. Light is added together to create form from out of the darkness. RGB stores individual values for red, green and blue. RGBA is RGB with an additional channel, alpha, to indicate transparency. RGB are the primary colors in light. In theory, all added together they make white. Common color spaces based on the RGB model include sRGB, Adobe RGB and Adobe Wide Gamut RGB. CMYK uses subtractive color mixing used in the printing process, because it describes what kind of inks need to be applied so the light reflected from the substrate and through the inks produces a given color. One starts with a white substrate(canvas, page, etc), and uses ink to subtract color from white to create an image. CMY are the primary colors in materials. In theory, all added together they make black. K is added to the printing inks because inks are not perfect, being organic and do not make a reliable black. The RBG color space is larger than the CMYK color space. They also over lap a little, creating colors that are exclusive to both color spaces. Black/White Grayscale Monotone: grayscale with a single, non-black ink Duotone, Tritone, Quattone (must convert to grayscale first) Multichannel: Converting CMYK to spot colors (printing: not used in RGB) LAB: Based on human perception of color. Monitor cannot display. Often used to make calculations when converting from one color mode to another (CMYK/RGB) Indexed Color: Whereas an RGB image specifies a red, green, and blue value separately for each pixel in the image, an indexed color image maintains a table that defines a number of predefined colors, and each pixel refers to a color in that table. Indexed color can greatly reduce file sizes for images—especially large ones—using only a few different colors (because each pixel needs only to use a few bits to refer to a space in the color table, rather than many bits to refer to subtle hues), but often results in very large file sizes for photographs or images with many subtle color shades. If an indexed color image has too small of a color table, gradients and other shadings can appear blocky (although dithering can be used in some cases to reduce this effect). GIF uses indexed color. Compresssion Lossy: Lossless: Compression Options o Dither is an intentionally applied form of noise, used to randomize quantization error, thereby preventing large-scale patterns such as contouring that are more objectionable than uncorrelated noise. Dither is routinely used in processing of both digital audio and digital video data, and is often one of the last stages of audio production to compact disc. Diffusion: Applies a random pattern that is usually less noticeable than Pattern dither. The dither effects are diffused across adjacent pixels. Pattern: Applies a halftone-like square pattern to simulate any colors not in the color table. Noise: Applies a random pattern similar to the Diffusion dither method, but without diffusing the pattern across adjacent pixels. No seams appear with the Noise dither method. o Interlacing is a method of encoding a bitmap image such that a person who has partially received it sees a degraded copy of the entire image. o Color Reduction Method and Colors specifies a method for generating the color lookup table and the number of colors you want in the color lookup table. Perceptual creates a custom color table by giving priority to colors for which the human eye has greater sensitivity. Selective creates a color table similar to the Perceptual color table, but favoring broad areas of color and the preservation of web colors. This color table usually produces images with the greatest color integrity. Selective is the default option. Adaptive creates a custom color table by sampling colors from the predominant spectrum in the image. For example, an image with only the colors green and blue produces a color table made primarily of greens and blues. Most images concentrate colors in particular areas of the spectrum. (Restrictive) Web uses the standard 216‑ color color table common to the Windows and Mac OS 8‑ bit (256‑ color) palettes. This option ensures that no browser dither is applied to colors when the image is displayed using 8‑ bit color. Using the web palette can create larger files, and is recommended only when avoiding browser dither is a high priority. Custom uses a color palette that is created or modified by the user. If you open an existing GIF or PNG‑ 8 file, it will have a custom color palette.
Pages to are hidden for
"What is a Bit"Please download to view full document