graphics basicss

7/27/2019 Graphics Basicss

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1 Dhanesha Senevirathne. ICT (2009/2010) Batch Collage of Technology KandyMy Notes-

Graphic design:

Pixel:

In digital imaging, a pixel (or picture element) is a single point in a raster image. The pixel is the smallest addressable screen element; 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 arranges 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 accuraterepresentations, 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.

Sub pixels:

For example, LCDstypically divide each pixel horizontally into three sub pixels. When the square pixel is dividing into three sub pixels, each sub pixel is necessarily rectangular. In the display industry terminology, sub pixels referred to as pixels, as they are the basic

addressable elements in a viewpoint of hardware, and they call pixel circuits rather than sub

pixel circuits.

This latter approach, referred to assub pixel rendering, uses knowledge ofpixel geometryto manipulatethe three colored sub pixels separately, producing a slight increase in the apparent resolution of color

displays. While CRT displays also use red-green-blue masked phosphor areas, dictated by a mesh grid

Many display and image-acquisition systems are, for variousreasons, not capable of displaying or sensing the different colorchannelsat the same site.

Therefore, the pixel grid is dividing into single-color regions thatcontribute to the displayed or sensed color when viewed at a

distance.

In some displays, such as LCD, LED, and plasma displays, thesesingle-color regions are separately addressable elements, which

have known as sub pixels.
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called the shadow mask, it would require a difficult calibration step to be align with the displayed pixel

raster, and so CRTs do not currently use sub pixel rendering.

Megapixel: A megapixel (MP or Mpx) is one million pixels, and is a term used for not only the number of

pixels in an image, but also to express the number of image sensor elements of digital cameras

or the number of display elements of digital displays.

For example, a camera with an array of 20481536 sensor elements is commonly said to have "3.1megapixels" (2048 1536 = 3,145,728). The megapixel count is use as a figure of merit, though it is

only one of the figures that determine camera quality.

Resolution: The measures dots per inch (dpi) and pixels per inch (ppi) are sometimes use interchangeably, but

have distinct meanings, especially for printer devices, where dpi is a measure of the printer's density

of dot

Standard display resolutions: The display resolution of a digital television or display device is the number of distinct pixels in each

dimension that can displayed.

It can be an ambiguous term especially as the displayed resolution is controlling by all different factorsin cathode ray tube (CRT) and flat panel or projection displays using fixed picture-element (pixel)arrays.

One use of the term display resolution applies to fixed-pixel-array displays such as plasma displaypanels (PDPs), liquid crystal displays (LCDs), Digital Light Processing (DLP) projectors, or similar

technologies, and is simply the physical number of columns and rows of pixels creating the display(e.g., 19201200).

A consequence of having a fixed grid display is that, for multi-format video inputs, all displays need a"scaling engine" (a digital video processor that includes a memory array) to match the incoming

picture format to the display.

Note that the use of the word resolution here is misleading. The term display resolution isusually used to mean pixel dimensions (e.g., 19201200), which does not tell anything about the

resolution of the display on which the image is actually formed.

In digital measurement the display resolution would be given in pixels per inch. In analog measurement, if the screen is 10 inches high, then the horizontal resolution is measured

across a square 10 inches wide.

This is typically stated as xxx lines horizontal resolution, per picture height. Example:

Analog NTSC and PAL TVs can typically display 480 (for NTSC) lines horizontal resolution,per picture height which is equivalent to 640 total lines from left-edge to right-edge.
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Selected standard display resolutions include:

Display resolution vs. native resolution in computer monitors: Computers can use pixels to display an image, often an abstract image that represents a GUI. The resolution of this image is calls the display resolution and is determined by the video card of the

computer.

LCD computer monitors also use pixels to display an image, and have a native resolution. Each pixel is made up of triads, with the number of these triads determining the native resolution. On some CRT monitors, the beam sweep rate may be fixed, resulting in a fixed native resolution. Most CRT monitors do not have a fixed beam sweep rate, meaning they don't have a native resolution

at all - instead they have a set of resolutions that are equally well supported.

To produce the sharpest images possible on an LCD, the user must ensure the display resolution of thecomputer matches the native resolution of the monitor. On a CRT with a fixed beam sweep rate, you

are required to use the native resolution. On a CRT without this restriction, you may use any

resolution supported by the monitor that matches the monitor's physical aspect ratio and it will lookfine. If the aspect ratio of the physical display and the selected resolution are different, many different

things can happen. On some LCDs, the monitor will stretch or squash the image to fill the entire

display.

On others, the aspect ratio will maintain while expanding the image to fit the display, resulting in blackbars on the top or sides of the image. This can also result in the image appearing blurry or jagged,depending on the native resolution of the display and the selected resolution on the computer.

For example, let's take the relatively common case of a full-screen application written assuming a 4:3aspect ratio running on a 16:10 aspect ratio widescreen display. If the selected resolution were

16001200 and you were running it on a 19201200 display that maintains aspect ratio while

expanding the image to fit, the image would not look blurry, because each pixel in the 16001200image maps to exactly 1 pixel on the 19201200 display.


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On yet other LCD monitors, if the selected resolution is less than the native resolution of the monitor,the monitor will display things in the selected resolution, with a black border around the edges.

Bits per pixel: The number of distinct colors that can be representing by a pixel depends on the number of bits per

pixel (bpp).

A 1 bpp image uses 1-bit for each pixel, so each pixel can be either on or off. Each additional bit doubles the number of colors available, so a 2 bpp image can have 4 colors, and a 3

bpp image can have 8 colors:

1 bpp, 21 = 2 colors (monochrome) 2 bpp, 22 = 4 colors 3 bpp, 23 = 8 colors 8 bpp, 28 = 256 colors 16 bpp, 216 = 65,536 colors ("High color" ) 24 bpp, 224 16.8 million colors ("True color")

Graphics:

Graphics often combinetext,illustration, andcolor. Clarity or effective communication may be the objective, association with other cultural elements

may be sought, or merely, the creation of a distinctive style.

Graphics can be functional or artistic. Graphic design basically is: Graphics (from Greek graphia) are visual presentations on some surface using text and/or

graphical elements. Your aim is to create something that is pleasing to the eye, such as a wall,

canvas, computer screen, paper, or stone to brand, inform, illustrate, or entertain and gets the

attention of the viewer. However, things cannot just look cool. They have to work as well. It may

consist of the deliberate selection, creation, or arrangement of typography alone, as in a brochure,

flier, poster, web site, or book without any other element.

Examples Photographs

Drawings Line Art Graphs Diagrams Typography Numbers, Symbols Geometric designs, Maps Engineering drawings
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What is Graphics Software?it is any kind of software which can be used to create, edit, and manage 2D computer graphics. These

computer graphics may be clip art, Web graphics, logos, headings, backgrounds, digital photos, or

other kinds of digital images.

Photoshop

Illustrator Paint Shop Pro

Graphic Industry: The Graphic Design industry relies on advertisers for its revenue. The current recession cut into a large slice of this industry's revenue, however, as demand from

advertising firms fell off.

As such, the past two years were poor ones for the Graphic Design and Advertising industries. The internet, however, is creating a new medium in which designers may specialize and is the industry's

largest growth segment.

The publishing sector is increasingly taking its products online, thus creating a new segment and demandfor qualified designers. In light of these trends and as the US economy recovers, the revenue forecast forthis industry will brighten but remain in a mature state.

Raster Graphics: A bitmap is basically an array of pixels with values indicating the color

The bitmap sizes are defined in pixels. BMP, TIF, GIF, JPG, PNG and most other graphics formatsare raster graphics

BMP records every pixels in the image, so the size is very big even for small images Image degrades when it is scale to a larger size

Raster Graphics Hardware

CorelDRAWThe GIMPMicrosoft Paint
http://graphicssoft.about.com/od/illustrator/http://graphicssoft.about.com/od/paintshoppro/http://graphicssoft.about.com/od/coreldraw/http://graphicssoft.about.com/od/coreldraw/http://graphicssoft.about.com/od/gimp/http://graphicssoft.about.com/od/gimp/http://graphicssoft.about.com/od/microsoftpaint/http://graphicssoft.about.com/od/microsoftpaint/http://graphicssoft.about.com/od/microsoftpaint/http://graphicssoft.about.com/od/gimp/http://graphicssoft.about.com/od/coreldraw/http://graphicssoft.about.com/od/paintshoppro/http://graphicssoft.about.com/od/illustrator/


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Vector graphics:A vector graphic contains the drawing

instructions other than the color value in

Pixels.

Like drawing a line drawing a rectangle,etc

It can be easily scaled without losing anycharacteristics

Vector Graphics Hardware

RGBcolor model:

The name of the model comes from the initials of the three additive primary colors, red, green,and blue.

RGB is a device-dependentcolor model: different devices detect or reproduce a given RGB valuedifferently, their response to the individual R, G, and B levels vary from manufacturer to

manufacturer, or even in the same device over time. Thus an RGB value does not define the same

coloracross devices without some kind of color management.

The main purpose of the RGB color model is for the sensing, representation, and display ofimages in electronic systems, such as,

Color TV and computer (CRT, LCD, plasma, etc.), Video cameras Image scanners Digital cameras Mobile phone displays Video projectors Multicolor LED displays large screens asJumboTron

Color printers, on the other hand, are not RGB devices, butsubtractive colordevices (typicallyCMYK color model).

Continuous & smooth lines

No filled objects random scan

refresh speed depends on

complexity of the scene
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CMYKcolor model:

Is a subtractive color model (process color, four color), used in color printing. CMYK refers to the four inks used in some color printing: cyan, magenta, yellow, and key black. However, it varies by print house, press operator, press manufacturer and press run, ink is typically

applies in the order of the abbreviation.

The CMYK model works by partially or entirely masking colors on a lighter, usually white, background. The ink reduces the light that would otherwise be reflecting. Such a model is call subtractive because inks subtract brightness from white. In additive color models such as RGB, white is the additive combination of all primary colored lights,

while black is the absence of light.

In the CMYK model, it is the opposite: white is the natural color of the paper or other background, whileblack results from a full combination of colored inks.

To save money on ink, and to produce deeper black tones, unsaturated and dark colors are produces byusing black ink instead of the combination of cyan, magenta and yellow.

Half toning: With CMYK printing, half toning (also called screening) allows for less than full saturation of the primary

colors.

A halftone image is made of a series of dots rather than a continuous tone. These dots can be different sizes, different colors, and sometimes even different shapes. Larger dots are

used to represent darker, more dense areas of the image, while smaller dots are used for lighter areas. Magenta printed with a 20% halftone, for example, produces a pink color, because the eye perceives the

tiny magenta dots and the white paper between the dots as lighter as and less saturated than the color ofpure magenta ink.

Without half toning, the three primary process colors could be printed only as solid blocks of color, andtherefore could produce only seven colors:

The three primaries themselves, plus three complementary colors produced by layering two

of the

Primaries (these subtractive complementary colors correspond roughly to the additive

primary colors):

Cyan and yellow produce green. Cyan and magenta produce a purplish blue. Yellow and magenta produce red plus layering all three of them resulting in black.

This close-up of printedhalftonerasters

show that magenta on top of yellow

appears as orange/red and cyan on top of

yellow appears as green.
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Halftone images use used in newspapers and magazines because it is a much more efficient way to printimages.

Since a halftone image is made of discreet dots, it requires significantly less ink to print than a continuoustone image.

As long as the resolution of the image (measured in LPI) is high enough, the dots appear as a continuousimage to the human eye.

However, if you closely examine the images printed in a newspaper, you should be able to see the dots thatmake up the halftone image.

Hex chrome: Hex chrome was a six-color printing process designed by Pantone Inc. In addition to custom CMYK inks. Hex chrome added orange and green inks to expand the color gamut, for better color reproduction. It also calls as a CMYKOG process. Pantone discontinued hex chrome in 2008 when Adobe Systems stopped supporting their software

[citation needed].

While the details of Hex chrome were not secret, use of Hex chrome was limit by trademark and patent tothose obtaining a license from Pantone.

CcMmYK color model: CcMmYK, sometimes referred to as CMYKLcLm, is a six color printing process used in

some inkjet printers optimized for photo printing.

It extends the customary four color CMYK process, which stands for Cyan, Magenta, Yellowand Key (black), by adding light cyan (lower case c) and light magenta (lower case m).

The light cyan and light magenta inks are essentially a washed out version of the cyan andmagenta inks.

Advantages of CcMmYK over CMYK: The most noticeable result of using light cyan and light magenta inks is the removal of a

distinct and harsh half toning dot appearance that appears in prints that use light shades of

cyan or magenta on the pure CMYK ink configuration.

Usually when printing a dark color the printer will saturate the area with colored ink dots, butwill use fewer ink dots to create the effect of a light color.

The result is hard to notice with Yellow because the human retina is not as sensitive to yellowas other colors.

However, the individual cyan and magenta ink dots will stand out in a sparse pattern due totheir darker color against a white background; the result is undesirable when it is notice.

By using light cyan or magenta, the printer can saturate areas that would typically use halftoning with these inks to remove the look of sparse magenta and cyan dots.

The downside however is the printer needs approximately twice as much light cyan/magentaink in areas to achieve the same saturation as pure cyan/magenta, which can lead to excess

ink usage.

The result however is significantly better for some photos.


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Screen angle: To improve print quality and reduce moir patterns, the screen for each color is set at a different

angle.

While the angles depend on, how many colors are used and the preference of the press operator,Typical CMYK process printing uses any of the following screen angles:

Benefits of using black ink:The black generated by mixing cyan, magenta and yellow primaries is unsatisfactory, and so four-color printing uses black ink in addition to the subtractive primaries. Common reasons for using

black ink include.

In traditional preparation of color separations, a red Keyline on the black line art marked the outline ofsolid or tint color areas. In some cases, a black key line is use when it served as both a color indicatorand an outline to be print in black. Because usually the black plate contained the Keyline, the K in

CMYK represents the key line or black plate also sometimes called the key plate.

Text is typically printed in black and includes fine detail (such as serifs), so to reproduce text or otherfinely detailed outlines using three inks without slight blurring would require impractically accurate

registration.

A combination of 100% cyan, magenta, and yellow inks soaks the paper with ink, making it slower todry, and sometimes impractically so. This also can cause the ink to bleed.

A combination of 100% cyan, magenta, and yellow inks often results in a muddy dark brown color thatdoes not quite appear black. Adding black ink absorbs more light, and yields much darker blacks.

Using black ink is less expensive than using the corresponding amounts of colored inks. When a very dark area is desirable, a colored or gray CMY bedding is applies first, then a full

black layer is applies on top, making a rich, deep black; this is called rich black. A black made

with just CMY inks is sometimes calling composite blackorprocess black.

The amount of black to use to replace amounts of the other ink is variable, and the choicedepends on the technology, paper and ink in use.

Processes called under color removal, under color addition, and gray componentreplacements is use to decide on the final mix; different CMYK recipes will be use depending

on the printing task.

C 100 15 105

M 15 45 75

Y 0 0 90

K 45 75 15

A color photograph of theTeton Range.
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Comparison with RGB displays: Since RGB and CMYK spaces are both device-dependent spaces. There no simple or general conversion formula that converts between them. Conversions generally done through color management systems, using color profiles that

describe the spaces being convert.

Nevertheless, the conversions cannot be exact, particularly where these spaces have differentgamut.

The problem is, computing a colorimetric estimate of color that results from print variouscombinations of ink has been address by many scientists.

A general method that has emerged for the case of halftone printing is to treat each tinyoverlap of color dots as one of 8 (combinations of CMY) or of 16 (combinations of CMYK)

colors.

Which in this context are known as Neugebauer primaries. The resultant color would be an area-weighted colorimetric combination of these primary

colors, except that the YuleNielsen effect ("dot gain") of scattered light between and within

the areas complicates the physics and the analysis; empirical formulas for such analysis have

been develops, in terms of detailed dye combination absorption spectra and empirical

parameters.

Other printer color models: CMYK or process color printing is contrast with

spot color printing, in which specific colored

inks are use to produce the colors appearing on

paper.

Some printing presses are capable of printingwith both four-color process inks and additionalspot color inks at the same time.

High-quality printed materials, such asmarketing brochures and books, may include

photographs requiring process-color printing,

other graphic effects requiring spot colors (such

as metallic inks), and finishes such as varnish,

which enhances the glossy appearance of the

printed piece.

CMYK process printers often have a relatively

small color gamut. Processes such as Pantone's

proprietary six-color (CMYKOG) Hex chrome

considerably expand the gamut. Light, saturated

colors often cannot be creating with CMYK, and

light colors in general may make visible the

halftone pattern. Using a CcMmYK process, with

the addition of light cyan and magenta inks to

CMYK, can solve these problems, and such a

process is used by many inkjet printers,

including desktop models


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Digital Printing:First - What is digital printing?

Printing digitally is a technology that permits the linking of printing presses to computers which

proves beneficial in a number of ways: faster turnaround times, lowered production and setup costs,

and the ability to personalize documents easier. This fairly new technology is prominent in the

printing industry because it's simply a more efficient way of printing.

Tip: When referring to digital printing you should be aware there are a couple of different ways to

describe it, Short-Run printing, and On-Demand printing; each term is used interchangeably. For a

good resource on printing terms check outPrinting-Press.org. Also check out theDo's and Don'ts of

printing.

Second - The Digital Process

1. Gathering your information, i.e. image, text, or both through an analog means like scanning in yourdocument or through a digital means like a digital camera or word processor document.

2.

Converting your information; your file format needs to be converted to a useable file, such as TIFF, orEPS.

3. Setting your layout.4. Printing can start almost immediately after your design and layout is set.

Third - Printing Methods in the Digital Realm

There are many different ways of printing in the digital printing realm. Here are some examples of

the methods used by printing companies:

Inkjet- Currently, inkjet printing is the primary printer technology for home, home offices, and manysmall businesses. Inkjet printers are inexpensive and produce good color output but can be slow. Bestresults are normally achieved when printing to specially coated inkjet or photo papers.
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Thermal Wax - Thermal wax printers produce vibrant color but require very smooth or speciallycoated paper or transparencies for best output. Thermal wax printing technology works well for

businesses that need to produce large quantities of transparencies for colorful business presentations.

Dye Sublimation - Dye-sublimation printing methods are favored by some graphic designers for high-end proofing and by some businesses that want to produce the best possible color materials in-house.

Electrostatic - Electrostatic printing is a process for printing or copying in which electrostatic forcesare used to form the image in powder or ink directly on the surface to be printed; the process basicallyusestonerinstead of ink to add color spotlessly to produce media, decorative or package printing.

Spray Jet - This printing process is similar to the Inkjet process, however the ink is applied to thesubstrateusing spray nozzles.

Dye-sublimation printers-These are known as dye-subs for short. They employ a printing processthat uses heat to transfer specially designed dyes to a medium such as a plastic card, paper or canvas.The dye-sublimation process consists of successive color passes using a ribbon that features separate

color panels. Dye-sub printers are proficient at high-quality color applications, including colorphotography. Once this technology became more accessible to be implemented, dye-sublimationprinters flooded towards consumer dedicated photo printer markets.

Toner-based laser printers- Laser printers produce high quality prints at good print speeds andthese devices are well known for their lowest cost-per-copy. Laser printers are also considered the

device of choice for many general-purpose office applications, but, when it comes to consumeradoption, it still remains an unpopular solution due to a high initial cost.
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Plotters-The true origins of this kind of printers presented vector graphics printing device thatconnected to a computer. Plotters printed their output by moving a pen across the surface of a piece ofpaper. This means that plotters were restricted to line art, rather than raster graphics as with the

other printing technologies. They could draw complex line art, including text, but did so comparatively

slower because of the mechanical movement of the pens. Because of this, plotters were incapable ofcreating a solid region of color; instead, they could hatch an area by drawing a number of close, regular

lines. They were mostly used in CAD applications, but with the emergence of faster and preciser laser

and ink technologies, they became obsolete. Nowadays, the term plotter is informally attributed to

large industrial inkjet or laser printers.

Advantages of Digital Printing

Cost - pre-press/setup costs are significantly lower than most plate printing methods. This makesmaking digital short runs much more affordable.

Size - Digital images can be produced in virtually any size. Output devices range in size from a fewinches wide to over sixteen feet in width. For even larger graphics, images can be "tiled" and

assembled in pieces. Turnaround time - Digital imaging allows quick turnarounds and the ability to change images "on the

fly." Most conventional printing methods involve proofs and setup. Digital printing simplifies the

process.

Printing has now recently caught up with the digital age utilizing digital means to help your business

produce your printing needs faster and less expensive than ever before. ThePrintGuide has a list of

Recommended Digital Printing Suppliers that are some of the best in the business for all of your

custom printing needs.
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Example Printer:

Canon's imageRUNNER series of network digital MFPs play a central role in document input and

output processes in the office.

The Printing Process

Imaging devices such as digital MFPs, laser beam printers and full colour copying machines employthe same electrophotographic printing principle.


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Offset printing: Offset printing is a commonly usedprintingtechnique where theinkedimage is transferred

(or "offset") from a plate to a rubber blanket, then to the printing surface. When used in

combination with thelithographicprocess, which is based on the repulsion ofoilandwater,

the offset technique employs a flat (planographic) image carrier on which the image to be

printed obtains ink from ink rollers, while the non-printing area attracts a water-based film

(called "fountain solution"), keeping the non-printing areas ink-free.Development of the offsetpress came in two versions: in 1875 by Robert Barclay ofEnglandfor printing on tin, and in

1903 by Ira Washington Rubel of theUnited Statesfor printing on paper.

Photo of fset Side view of the offset printing process. Multiple ink rollers are

used to distribute and homogenize the ink.

The most common kind of offset printing is derived fromthe photo offset process, which involves using light-

sensitive chemicals and photographic techniques to

transferimagesandtypefrom original materials to printingplates.

In current use, original materials may be an actualphotographic print and typeset text. However, it is more

common with the prevalence of computers and digital

images that the source material exists only as data in a

digital publishing system.

Offset litho printing on to a web (reel) of paper is commonlyused for printing of newspapers and magazines for high

speed production.

How ink is transferred from the ink duct to the paper has several steps.

1. Ink duct roller delivers ink from the ink duct to the ink pyramid.2. The drop roller transfers ink from duct roller to distribution roller. It is never in contact with both

rollers at the same time.3. The distribution rollers evenly distribute the ink. The first distribution roller picks up the ink from

driving rollers, and the last distribution rollers transfer the ink to the form rollers.

4. The transfer rollers transfer ink between the ink-absorbing and ink-delivering driving rollers.5. Driving rollers roll against the distribution rollers and either absorb or deliver ink, depending on their

placement.6. Ink form rollers transfer ink from the last distribution rollers on to the printing plate.7. The printing plate transfers the ink to the offset cylinder(typically called blanket cylinder) usually

covered with a rubber 'blanket'.

8. The paper is then pressed against the blanket cylinder by the impression cylinder, transferring the inkonto the paper to form the printed image.

Types of paper feed1. Sheet-fed litho

"Sheet-fed" refers to individual sheets of paper or paperboard being fed into a press. A lithographic

("litho" for short) press uses principles of lithographyto apply ink to a printing plate, as explainedpreviously. Sheet-fed litho is commonly used for printing of short-run magazines, brochures, letter

headings, and general commercial (jobbing) printing.
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2. Web-fed litho"Web-fed" refers to the use of rolls (or "webs") of paper supplied to the printing press. Offset web

printing is generally used for runs in excess of 10 or 20 thousand impressions. Typical examples of

web printing include newspapers, newspaper inserts/ads, magazines, catalogs, and books. Web-fed

presses are divided into two general classes: "Cold" or "Non-Heat set," and "Heat set" offset web

presses, the difference being how the inks that are used dry. Cold web offset printing dries through

absorption into the paper, while heat set utilizes drying lamps or heaters to cure or "set" the inks.

Heat set presses can print on both coated (slick) and uncoated papers, while coldest presses arerestricted to uncoated paper stock, such as newsprint. Some coldest web presses can be fitted with

heat dryers, or ultraviolet lamps (for use with uv-curing inks). There is also another possibility of

adding a drier in a cold-set press and making it as a semi-commercial press. It is a concept where a

newspaper can print color pages in heat set and BW pages in coldest.

3. Web press v. sheet-fed (photo offset)Sheet-fed presses offer several advantages, because individual sheets are fed though, a large number

of sheet sizes and format sizes can be run through the same press. In addition, waste sheets can be

used for make-ready which allows for lower cost make readies, so that good paper is not wasted

while setting up the press, for plates & inks (waste sheets do bring some disadvantages as often

there are dust, offset powder particles that transfer on to the blankets and plate cylinders, thereby

creating imperfections on the printed sheet in the form of "hickies").

Web-fed presses, on the other hand, are much faster than sheet-fed presses, they are roll fed (no

sheets, and most rolls come in 17" & 34" sizes, and weigh up to 1000 lbs) The speed of the web press

is in excess of 20,000 cutoffs per hour. Their speed makes them ideal for large runs such as

newspapers or magazines. However, web-fed presses have a fixed cut-off, unlike other presses such

as rotogravure or flexographic presses.

Types of platemakingGenerally, the plates used in offset printing are thin, and are mostly made of aluminum, thoughsometimes can be made of multimodal, paper, or plastic.

1. Polyester platesPolyester plates can be used in place of aluminum plates for smaller formats or medium quality jobs,

as their dimensional stability is lower (Kipphan 209).

2. Computer to Plate (CTP) / Direct to Plate (DTP)Computer to Plate (CTP) is a newer technology that allows the imaging of metal or polyester plates

without the use of film. Eliminating the stripping, compositing, and traditional plate making

processes, CTP revolutionized the printing industry and led to reduced prepress times, lower costs of

labor, and improved print quality.

Most CTP systems used thermal CTP as opposed to violet CTP, though both systems are effective,

depending on the needs of the printing job. Thermal CTP does have the advantage of extremely high

quality, but Violet CTP does cost significantly less. Thermal plates are generally used for longer runs,

while Violet CTP is employed for shorter runs, and popular with 2-up and 4-up applications (Bruno,

Romano, and Riordan 126).

Thermal CTP has the added bonus of utilizing binary exposure, which limits the risk of under or

overexposure, and makes it possible to work under yellow light (Bruno, Romano, and Riordan 126).

Thermal CTP involves the use of thermal lasers to expose and/or remove areas of coating while theplate is being imaged. This depends on whether the plate is negative, or positive working. These

lasers are generally at a wavelength of 830 nanometers, but vary in their energy usage depending on


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Acid-based fountain solutions are still the most common variety and yield the best quality results by

means of superior protection of the printing plate, lower dot gains, and longer plate life. Acids are

also the most versatile, capable of running with all types of offset litho inks. However, because these

products require more active ingredients to run well than do neutrals and alkalines, they are also the

most expensive to produce. That said, neutrals and, to a lesser degree, alkalines are still an industry

staple and will continue to be used for most newspapers and many lower-qualityinserts.

In recent years alternatives have been developed which do not use fountain solutions at all

(waterless printing).

Advantages of offset printing compared to other printing methods include:

Consistent high image quality. Offset printing produces sharp and clean images and type more

easily than letterpress printing because the rubber blanket conforms to the texture of the

printing surface.

Quick and easy production of printing plates.

Longer printing plate life than on direct litho presses because there is no direct contact between

the plate and the printing surface. Properly developed plates running in conjunction with

optimized inks and fountain solution may exceed run lengths of a million impressions.

Cost. Offset printing is the cheapest method to produce high quality printing in commercialprinting quantities.

Disadvantages of offset printing compared to other printing methods include:

Slightly inferior image quality compared to rotogravure or photogravure printing.

Propensity for anodized aluminum printing plates to become sensitive (due to chemical

oxidation) and print in non-image/background areas when developed plates are not cared forproperly.

Time and cost associated with producing plates and printing press setup. As a result, very small

quantity printing jobs are now moving to digital offset machines.

IdentificationEvery printing technology has its own mark so has the offset printing. In text reproduction the type

edges are sharp and have clear outlines (see following picture). The paper surrounding the ink dots

is usually unprinted. The halftone dots are always irregular and blurry though there are different

screening methods.

In industryOffset lithography became the most popular form of commercial printing in the 1950s ("Offset

Printing"). Subsequent improvements in plates, inks, and paper enhanced the technology and

maximized its superior production speed and plate durability. Today, lithography is the dominant

printing technology in the US, and most lithography is printed as offset lithography.Today, offset

lithography is "responsible for over half of all printing using printing plates" (Bruno, Romano and

Riordan 137). The quality of the prints made is consistently high, and the volume of prints created

for their respective cost makes commercial offset lithography very efficient for businesses, especially

when many prints must be created quickly.
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Other Things you may know about graphs and its industry:

1. Image Types & File formats:2. Import and Export functions in graphic applications:

3. Printing Technology:i. Paper selection

ii. Other printing materials Papers, ink etc.iii. Color separation methods/ machine (industry)iv. Printing Methods

Digital printers, offset printers (Industry) Plate maker, Paper cutter etc. (Industry)v. Designing layouts

Measurement Page design Background

vi. Applying colorvii. Working with fonts

viii. Photo editing4. Copyright issues & Observe ethics & norms in graphic industry.[

5. The hardware dependency and requirements for graphic software:6. The different between platforms(Apple, IBM ) effects graphic quality:

Reference: Wikipedia and Google

graphics basicss

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