Screen Frequency / Resolution

Resolution can be confusing, even for people who have been working in the trade for a long time. This is largely due to the fact that, in digital technology, resolution has to be considered in both the input stage (scan) and the output stage (Imagesetter or laser printer). Understanding these two resolutions is vital to the process of getting high-quality images.

Halftone Spots
Halftone spots are the result of turning off and/or on the dots in a halftone cell. This is how an imagesetter creates variant dot sizes.

Screen Frequency (Line Screen)
The number of rows or Lines Per Inch lines of spots in a halftone image within a given distance (lpi). Screen frequency effects the size and sharpness of the halftone spots the imagesetter will render. Choosing the correct screen frequency will depend on such things as the type of paper it will be printing on and the amount of dot gain expected on the press.

Resolution Specifications

LPI	Imagesetter Resolution
133 LPI	2400 DPI
150 LPI	2400 DPI/3000 DPI
175 LPI	3000 DPI

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Advance Scanning

What makes a good scan? In order to ensure a high quality reproduction, the initial scan must capture as much detail as possible. Check your scan against your original image to ensure that you've maintained as much detail as possible. This can take several rescans. You should also expect to do some tonal manipulation in Photoshop or other image editing program. Tonal manipulation is the key to setting the right contrast, overall tonal range and getting the most detail possible within the limitations presented by the paper and printing choices. See below for the tonal range specifications for specific paper stock types.

Screen Angles
When working with multiple colors that overlap, such as duotones or CMYK, it is necessary to angle the halftone screens. To avoid moire patterns, angle the screen 30 degrees apart.

Tonal Range Specifications

Stock	Shadow Dot	Highlight Dot
Uncoated Stock	80-87%	3-5%
Matte Stock	87-92%	5-7%
Gloss/Dull Stock	92-97%	7-10%

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How to Fix a Stuck Pixel on an LCD Monitor

If your LCD screen has a stuck or dead pixel (a point on the screen that is always lit or always dark), it is usually due to a transistor malfunction or uneven distribution of liquid in the liquid crystal display (TFT LCD). This can often be fixed.

Steps....

Software Method

1. Try running pixel fixing software (see Sources and Citations). Stuck pixels can often be re-energized by rapidly turning them on and off. If this fails, complete the following steps.

Pressure Method

1. Turn off your computer's monitor.
2. Get yourself a damp washcloth, so that you don't scratch your screen.
3. Take a household pen, pencil, screwdriver, or some other sort of instrument with a focused, but relatively dull, point. A very good tool would be a PDA stylus.
4. Fold the washcloth to make sure you don't accidentally puncture it and scratch the screen.
5. Apply pressure through the folded washcloth with the instrument to exactly where the stuck pixel is. Try not to put pressure anywhere else, as this may make more stuck pixels.
6. While applying pressure, turn on your computer and screen.
7. Remove pressure and the stuck pixel should be gone. This works as the liquid in the liquid crystal has not spread into each little pixel. This liquid is used with the backlight on your monitor, allowing different amounts of light through, which creates the different colors.

Tapping Method

1. Turn on the computer and LCD screen.
2. Display a black image, which will show the stuck pixel very clearly against the background. (It is very important that you are showing a black image and not just a blank signal, as you need the backlighting of the LCD to be illuminating the back of the panel).
3. Find a pen with a rounded end. A Sharpie marker with the cap on should be fine for this.
4. Use the rounded end of the pen to gently tap where the stuck pixel is - not too hard to start with, just enough to see a quick white glow under the point of contact. If you didn't see a white glow, then you didn't tap hard enough, so use just slightly more pressure this time.
5. Start tapping gently. Increase the pressure on the taps gradually for 5-10 taps until the pixel rights itself.
6. Display a white image (an empty text document is good for this) to verify that you haven't accidentally caused more damage than you fixed.

Tips....

• If the pressure and tapping don't work directly on the stuck pixel, start moving outward around the stuck pixel. If you see the pixel flicker while doing this then you know where you can focus the pressure and tapping techniques rather than directly on the pixel.
• Many people report success with this technique but these instructions won't work in every case. It may take a few attempts to make sure you are pressing exactly on the stuck pixel.
• These instructions will fix "stuck" pixels, not "dead" ones. Dead pixels appear black while stuck pixels can be one constant color like red, blue or green.
• An alternative, but similar technique involves gently massaging the stuck pixel with a warm damp (not wet) soft cloth.
• Alternative technique to tapping: Using a rounded pencil eraser, push with moderate pressure into screen at stuck pixel.
• If these instructions don't work, you can hopefully get the monitor replaced through your manufacturer. If your monitor falls under the specifications of replacement, get in contact with the manufacturer to set up replacement plans.
  

Warning....

• Do not attempt to open the monitor as it will void the warranty and the manufacturer will not replace it.
• Make sure you don't get any electrical equipment wet or it may break.
• Some people claim that touching the screen can cause more pixels to become stuck, although this has not been proven.

  

• Sub-Pixel Layers
  LCD Displays are composed of multiple layers. Each layer is separated by ve ry small glass spacers. These spacers and the individual layers are very delicate. Rubbing an LCD panel with a finger or even a cloth can cause the spacers to break and cause further issues beyond the original pixel fault. As such most repair technicians with service certifications are trained not to use the rub or tap methods - use them at your own risk.
• Most LCD manufacturer warranties for LCD displays will cover replacement of the panel when the display reaches a certain number of pixel anomalies. These warranties however generally will not cover damage caused by rubbing the screen so use extreme caution and contact the manufacturer before proceeding to see if you qualify for repair or replacement.

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What is LCD Monitor?

LCD stands for Liquid Crystal Display, referring to the technology behind these popular flat panel monitors. An LCD monitor is distinguishable from a traditional CRT monitor as the latter has a bulky footprint with a depth of several inches and a weight of 30 - 50 pounds (13 - 23 kilograms) or more, while LCDs are commonly 1 - 3 inches (2.5 - 7.5 cm) thick and weigh less than 10 pounds (4.5 k).

LCD displays were used on laptop computers before the technology improved enough to make the jump to desktop monitors. An LCD monitor consists of five layers: a backlight, a sheet of polarized glass, a "mask" of colored pixels, a layer of liquid crystal solution responsive to a wired grid of x, y coordinates, and a second polarized sheet of glass. By manipulating the orientations of crystals through precise electrical charges of varying degrees and voltages, the crystals act like tiny shutters, opening or closing in response to the stimulus, thereby allowing degrees of light that have passed through specific colored pixels to illuminate the screen, creating a picture.

As LCD technology evolves, different techniques for producing color emerge. Active-matrix or TFT (thin film transistor) technology produces color and images as sharp as any CRT and is generally considered superior to passive-matrix technologies.

Important specifications to consider when shopping for an LCD monitor include contrast ratio, brightness (or "nits"), viewing angle, and response time.

Contrast ratio relates to the display's comparative difference between its brightest white values and its darkest black values. A higher contrast ratio will have truer colors with less "wash out." The standard offering for lower end models is commonly 350:1. Many experts recommend a contrast ratio of 500:1 or better.

An LCD monitor is brighter than a CRT, giving the consumer little reason to hunt for an especially bright model. Brightness is measured in nits, or one candela per square meter. Anywhere from 250 - 300 nits is standard. If the nits are much higher you'll likely end up adjusting the brightness way down.

The viewing angle is an especially important consideration if you plan to have multiple people viewing the LCD monitor at any given time. There is a vertical and a horizontal viewing angle specification, which refers to the degree you can stray from dead center before the picture starts to wash out. High contrast levels usually go hand-in-hand with wider viewing angles. Many recommend a viewing angle of at least 140 degrees horizontal and 120 degrees vertical. The wider the viewing angles, the better.

Response time is measured in milliseconds (ms) and refers to how long it takes pixels to turn from completely white to black and back again. Smaller values represent a faster response time and are more desirable, especially for gaming or viewing video. If the response time is slow, "ghosting" or "trailing" can occur with fast-moving images, as repaints of the screen overlap. A maximum response time should be no more than 25ms for general use, and 17ms is better. Many gamers report no ghosting using an LCD monitor with a response time of 16ms or less.

LCDs use only one-third to one-half the electricity of their CRT counterparts. They are much easier on the eyes, take up 90% less space, and only weigh a few pounds. They also emit far less low-frequency radiation than CRTs. This makes LCDs a great choice for nearly everyone, and ideal for people who work all day in front of the screen. Colors may change hue as one moves to the outer limits of the viewing angle, particularly on displays with narrow viewing angles and low contrast ratios. For this reason graphics professionals that require exacting color consistency regardless of viewing angle generally use CRTs, though LCDs have improved in this regard.

An LCD monitor comes in standard sizes from 15-inches to 21-inches, and larger. The viewing screen is the same size as the rated display, unlike CRT monitors. Therefore a 15-inch LCD will have a 15-inch viewing screen.

A potential weak link of an LCD monitor is the backlight. Many monitors come with a 3-year warranty, but stipulate 1 year for the backlight. Models with 3-year warranties that cover the backlight usually cost a little more but may be worth the extra investment.

Reflective twisted nematic liquid crystal display.

1. Polarizing filter film with a vertical axis to polarize light as it enters.
2. Glass substrate with ITO electrodes. The shapes of these electrodes will determine the shapes that will appear when the LCD is turned ON. Vertical ridges etched on the surface are smooth.
3. Twisted nematic liquid crystal.
4. Glass substrate with common electrode film (ITO) with horizontal ridges to line up with the horizontal filter.
5. Polarizing filter film with a horizontal axis to block/pass light.
6. Reflective surface to send light back to viewer. (In a backlit LCD, this layer is replaced with a light source.)

A liquid crystal display (LCD) is an electro-optical amplitude modulator realized as a thin, flat display device made up of any number of color or monochrome pixels arrayed in front of a light source or reflector. It is often utilized in battery-powered electronic devices because it uses very small amounts of electric power.

A comprehensive classification of the various types and electro-optical modes of LCDs is provided in the article LCD classification.

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What is a CRT Monitor?

CRT stands for cathode ray tube, describing the technology inside an analog computer monitor or television set. A CRT monitor or TV is readily recognizable by its bulky form. LCD monitors and plasma television sets, or flat panel displays, use newer digital technologies.

The CRT monitor creates a picture out of many rows or lines of tiny colored dots. These are technically not the same thing as pixels, but the terms are often used interchangeably. The more lines of dots per inch, the higher and clearer the resolution. Therefore 1024 x 768 resolution will be sharper than 800 x 600 resolution because the former uses more lines creating a denser, more detailed picture. Higher resolutions are important for displaying the subtle detail of graphics. For text, resolution isn't as critical.

But how do those colored dots appear on the screen?

Inside a CRT monitor is a picture tube that narrows at the rear into a bottleneck. In the bottleneck is a negative charged filament or cathode enclosed in a vacuum. When electricity is supplied, the filament heats up and a stream or "ray" of electrons pour off the element into the vacuum. The negatively charged electrons are attracted to positively charged anodes which focus the particles into three narrow beams, accelerating them to strike the phosphor-coated screen. Phosphor will glow when exposed to any kind of radiation, absorbing ultraviolet light and emitting visible light of fluorescent color. Phosphors that emit red, green and blue light are used in a color monitor, arranged as "stripes" made up of dots of color. The three beams are used to excite the three colors in combinations needed to create the various hues that form the picture.

To precisely direct the beams, copper steering coils are used to create magnetic fields inside the tube. The fields move the electron beams vertically or horizontally. By applying varying voltages to the steering coils, a beam can be positioned at any point on the screen. Each image is painted on the screen -— and repainted -- several times each second by scanning the electron beams across the screen at incredible rates. This must be done even when the picture being displayed is unchanging, because the phosphor only glows for a very short time.

The refresh rate indicates how many times per second the screen is repainted. Though monitors differ in their capabilities, lower resolutions normally have higher refresh rates because it takes less time to paint a lower resolution. Therefore a setting of 800 x 600 might have a refresh rate of 85Hz, (the screen will be repainted or refresh 85 times per second), while a resolution setting of 1024 x 768 may have a refresh rate of 72Hz. Still higher resolutions usually have refresh rates closer to 60Hz. Anything less than 60Hz is generally considered inadequate, and some people will detect "flicker" even with acceptable refresh rates. Generally speaking, high-end monitors have higher refresh rates overall than lower-end models.Another specification regarding CRT monitors is "dot pitch" which relates to the tightness or sharpness of the picture. A lower dot pitch such as .25 is preferable over a higher dot pitch. In the heydey of the CRT monitor this was an issue because some models were sold with .32 dot pitch, resulting in "fuzzy" text. By the end of the CRT era, virtually all displays had .28 or better and today's CRT monitors can have dot pitches as low as .21.

The CRT monitor comes in 15-inch to 21-inch sizes (38 — 53 cm) and larger, though the actual viewing screen is about 1 inch (2.5 cm) smaller than the rated size. Screens are measured diagonally from corner to corner, including the case.

Tried, true, dependable and economical, CRT technology ruled for decades before its dethroning in the late 1990s - early 2000s. Negatives of the CRT include radiation emission, high power consumption, weight and bulk.

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