Berikut bbrp catatan mengenai kata2 aneh (buzz words) yg sering digunakan dlm digital image dan warna:
Dlm digital imaging:
Bitmap –> a type of memory organization (image file format) used to store digital images. Bitmap = pixmap = map of bits = map of pixels.
Bit = binary digit –> basic unit information that tells the amount of information stored by a digital device.
Image file formats –> standardized ways of organizing and storing digital images.
Graphic file formats –> berupa raster dan vector.
Raster format –> it stores images as bitmaps (pixmaps). Quality of images depend on the scale.
Type of file format: JPEG/JFIF, JPEG 2000, Exif, TIFF, RAW, PNG, GIF, BMP (windows bitmap), PPM, PGM, PBM, PNM, WEBP, JPEG XR, TGA, ILBM, PCX, ECW, IMG, SID, CD5, FITS, PGF, XCF PSD, PSP.
Vector format –> contain a geometric description (e.g. points, lines, curves, any shape, which are all based on mathematical equations) to represent images in computer graphics. This format can be scaled or rendered smoothly at any desired display size without degrading quality. It can contain bitmap data as well. To be displayed on digital monitors, all vector graphics must be rasterized.
Type of file format: CGM, SVG, AI, CDR, EPS< HVIF< ODG< PDF, PGML, SWF, VML, WMF/EMF, XAR, XPS
Image file sizes (number of bytes) –> increases with the increase of the number of pixels composing an image as well as the color depth of the pixels
- The greater the number of rows and columns, the greater image resolution, the larger the file
- Color depth examples: 8-bit pixel (1 byte) = 256 colors, 24-bit pixel (3 bytes) = 16 million color (true colors)
Image file compression algorithms:
- Lossless compression –> reduce file size without losing image quality, not as small a file as a lossy compression file
- Lossy compression –> take advantage of the inherent limitations of the human eye and discard visible information
Color depth = bit depth –> number of bits used to represent the color of a single pixel (bits per pixel).
True color –> 24-bit color, uses 8 bits for each color (RGB). 28 = 256 levels of each of the color, which makes a combination of more than 16 million mixed colors.
Raster Image Processor (RIP) –> a tool to produce a raster image (bitmap), which is then sent to a printing device. Input for RIP:
- Page description language (PDL) –> language that describes the appearance of a printed page in a higher level than an actual output bitmap. Such as: FP, CPCL, Diablo, DPL, DTPL, DVI, EPL, ESC/P, ESC/P2, HP-GL, InterPress, IPDS, KPDL, LCDS, MODCA, PCL, PDF, PostScript, PPDS, RPCS, SPL, SVG, XPS, ZJS, ZPL
- Another bitmap of higher or lower resolution than the output device –> which RIP can apply either smoothing or interpolation algorithms to the input bitmap to generate the output bitmap
Stages of RIP:
- Interpretation –> the PDLs are translated into a private internal representation of each page.
- Rendering –> the private internal representation is turned into a continuous tone bitmap. In practice, interpretation and rendering are frequently done together.
- Screening –> the continuous tone bitmap has to be converted into a halftone (pattern of dots) before printing. Two methods:
- Amplitude modulation (AM) screening –> dot size varies depending on the object density; dots are placed in a fixed grid
- Stochastic or Frequency modulation (FM) screening –> dot size remains constant; dots are placed in random order to create darker or lighter areas of the image; dot placement is precisely controlled by sophisticated mathematical algorithms
Dlm manajemen warna (color management) antara alat2 visual elektronik:
Profile connection space (PCS) –> menggunakan dimensi warna CIELab or CIEXYZ
ICC profile –> a set of data that characterizes a color input or output device or a color space, according to ICC.
Rendering –> a process to solve the mismatch of color gamut. Two of most important rendering types are relative colorimetric and perceptual rendering.
Relative rendering –> maintains an exact relationship between the in gamut colors, and cuts out the out gamut colors
Perceptual rendering –> tries to preserve some relationships between the out gamut colors, and makes inaccuracies in the in gamut colors.
Reference illuminant of the PCS is 16-bit fractional approximation of D50 (its white point is XYZ = (0.9642, 1.000, 0.8249)
Cone cells (cone) –> photoreceptor cells in the retina of the eye that are responsible for color vision. They function best in relatively bright light (~ 4.5 million cone cells in the human retina). Less sensitive to the light
Rod cells (rod) –> photoreceptor cells in the retina of the eye that can function in less intense of light; concentrated at the outer edges of the retina; used in peripheral vision (92 million rod cells); entirely responsible for night vision
Retina –> light sensitive tissue lining the inner surface of the eye; the optics of the eye create an image of the visual world on the retina, which serves much the same function as the film in a camera.
Photoreceptor cell –> specialized type of neuron found in the eye’s retina that is capable of phototransduction
Phototransduction –> a process by which light is converted into electrical signals in the rod cells, cone cells, and photosensitive ganglion cells of the retina of the eye
Color vision –> capacity of an organism or machine to distinguish objects based on the wavelengths (or frequencies) of the light they reflect, emit, or transmit.
Trichromacy –> condition of possessing 3 independent channels for conveying color information, derived from the 3 different cone types.
Incandescent lighting –> light seen from thermal radiation of heating of an object (e.g. sun, light bulb filament of tungsten, candle)
Incandescent lighting of light bulbs –> tungsten filament is heated till about 2500oC by the electricity. Then it radiates visible light only 12% of the energy supplied. The other 88% is in the form of heat. In the sealed bulb, a mixture of N2 and Ar is allowed. No O2 is allowed, otherwise it will burn.
Incandescence –> light occurs at high temperatures
Luminescence –> light occurs at low temperatures
Fluorescent lamp –> gas-discharge lamp that uses electricity to excite mercury vapor (atoms), which then produce short wave UV light that causes a phosphor to fluoresce, producing visible light
Fluorescence –> emission of light by a substance that has absorbed light (or other electromagnetic radiation) of a different wavelength. In most cases, emitted light has a longer wavelength, and therefore lower energy, than the absorbed radiation.
Gas-discharge lamps –> artificial light sources that generate light by sending an electrical discharge (movement of electrons due to potential different) through ionized gas.
Spectral power distribution –> power of an illumination (Watt) per area (m2) and wavelength (m).
RGB color model –> Red Green Blue; device dependent color model (e.g. phosphors, dyes, manufacturers, time); it is an additive primary colors that means that the 3 light beams are added together, and their light spectra add, wavelength for wavelength, to make the final color’s spectrum. Zero intensity for each component gives the darkest color (no light = black), and full intensity of each gives a white
Additive color –> involves light emitted directly from a source. It starts without light (black). Light sources of various wavelengths combine to make a color
Subtractive color –> mixing of paints, dyes, inks, and natural colorants to create a full range of colors, each caused by subtracting (absorbing) some wavelengths of light and reflecting the others. It starts with light or white light
Color model –> abstract mathematical model describing the way colors can be represented as sequences of numbers.
Color space –> gamut + color model.
Metamerism –> matching of colored objects with different spectral power distribution. Colors that match this way are called metamers.
Metamerism failure –> two or more colored objects which looked the same under one light source, but different under another light source.
Dot gain (tone value increase) –> the degree to which a dot of ink enlarges when it comes in contact with paper. For example, when a 50% ink dot is laid onto paper, it might spread to present the visual appearance of a 70% dot.
Total area coverage (TAC) = total ink coverage (TIC) = total dot area –> maximum combination of all CMYK inks for one spot on a paper. This cannot exceed a specified value, otherwise the inks may not transfer effectively and the printed sheets may not dry properly. This is limited to 300% for offset lithography using coated paper.