Chap24

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Chap24

  1. 1.  Explain the meaning of monitor resolution and output device resolution.
  2. 2. In This Chapter, you’ll learn on:  Explain PPI and DPI  Measure an output device resolution.  Describe monitor and image bit depth.  Identify the various monitor resolutions and printer resolution
  3. 3. Explain PPI and DPI There are different type of resolution in computer graphics.  Pixels per inch, or PPI is used to measure monitor resolution or commonly known as screen resolution.  Dots per inch or DPI is used in reference to printers, imagesetters, and other paper-outputting devices. DPI is also refers as printer resolution or printed image resolution.  Samples per inch or SPI is used when referring to scanners.
  4. 4. Monitor Resolution and Printing resolution There are two different levels of resolution that a designer might use; monitor resolution and printing resolution. Monitor resolution  means how clear the image is when it is displayed onscreen, the recommended resolution setting is somewhere between 72 PPI and 96 PPI, even though resolution isn’t really a factor in preparing screen images. That’s just because monitors display somewhere in the 72 to 96 PPI range.
  5. 5. Printing resolution  means how clearly an image will print on a printer or in professional printing uses. Laser printers and inkjet printers used to output film for professional printing require more information than is available in a 72 DPI file to produce a smooth and clear image. How much more depends on the bit depth of the image. Note: DPI is the more common term and is often used interchangeably with PPI when referring to on-screen images.
  6. 6. Measure an output device resolution  Have you ever downloaded an image from the internet and then printed it, only to get results that were, well, less than you expected? The image looked great on your computer screen, but when you printed it, it either printed at the size of a postage stamp or when you try to get it printed at a decent size, it will look blurry or "blocky"? The culprit is image resolution. What you see on-screen is not necessarily what you'll see on the printed page.  This is due to the fact that an image will only requires a resolution of 72 DPI to appear clear on screen, but it requires a higher DPI (at least 200 DPI) for printing. An image with only 72 DPI resolution contains less information than one that is 300 DPI.
  7. 7. Measure an output device resolution  In order to determine the resolution of an image you need to know which printer you are going to use. However, to store an image in a higher resolution than the printer can print is no use. For example, if you scan an image in resolution higher than 300 DPI is redundant if you are only going to print the image on an ordinary laser printer. The image quality will not improve in printing; it will just take longer to print.
  8. 8.  Black and white (1-bit) bitmap images are actually pretty easy to understand in this regard. A designer doesn't need any more resolution in an image than the resolution of the final printing device. This means that, if the image is being final printed on a 600dpi laser printer (a cheap flyer perhaps), the images need resolution of 600dpi at 100%.  Grayscale and color bitmap images (8–32-bit) are a little bit more tricky. One needs to know how the image will be output and at what halftone screen (linescreen) before scanning an image. The linescreen refers to the number lines (of dots) per inch (LPI) that will be used to simulate tones of color and gray in the printing process. A typical linescreen for a laser printer is 85lpi. A newspaper's screen is usually between 85 – 120 LPI and a magazine is often between 133 and 150 LPI.
  9. 9.  A bitmap image's resolution should be twice the linescreen.  That is to say that, in the case of a laser printer, an image would require 170 DPI for the best appearance on a printer using 85 LPI.  A color magazine would require an image be 300 DPI for best reproduction at 150 LPI.  Anything less will cause an image to deteriorate and pixelate. The amount of the deterioration depends on how much lower the resolution is than what it should be.  Monitor and Web resolution (72 DPI) is a far cry from printing resolution. Don't even consider using that.
  10. 10. Describe monitor and image bit depth Monitor A Monitor is the most visual part of a computer system. We see it first and stare at it for much of the day. It provides a window into the Internet or into the workings of a computer. But, are they all the same? Hardly — as anyone who has gone through a catalog or visited a computer showroom can attest. A monitor is quite simply the term that we give for a display screen and the outer shell that contains it. There are several different ways to classify monitors. The most common is in terms of color capabilities. They are broken into three categories:
  11. 11. Describe monitor and image bit depth Monitor The most common is in terms of color capabilities. They are broken into three categories:  Monochrome monitors display two colors; one for the foreground (or text) and one for the background. Commonly these colors are black and white.  Grayscale monitors display different shades of gray. In the not- too-distant past, larger color monitors were so expensive that large grayscale monitors were common for design use.  Color monitors display anywhere between 16 and millions of colors. These monitors display colors by using three separate signals known as RGB signals (red, green, blue) not unlike a TV set. Today, unless you're working with really old equipment, you'll be hard pressed to find anything but a color monitor being used.
  12. 12. Monitors are then classified by the size of the screen. Like a television, the screen sizes are measured diagonally so size can be misleading. The standard monitor size today is 20" with 21" monitors very quickly becoming the norm. There is a significant jump in price once you jump to the 24" and 32" sizes.
  13. 13. Bit Depth  A "bit" in computer language refers to the smallest amount of information that a computer can understand. It is an electronic pulse that contains one of two characters. It contains either a 1 or a 0 and can either signal on or off. Bit depth refers to the number of bits found in a graphics file or that can be displayed on a monitor.  Pixels, which make up a monitor's screen to display an image, are made up of bits. The more bits that are contained in the pixel, the greater the bit depth. The greater the bit depth, the more colors can be displayed at one time. This is also true of a graphics file. Bit depth of a graphics file indicates the amount of color in that file. As you might expect, greater bit depth brings greater file size. A 4" x 5" RGB photo (24-bit depth) will have a bigger file size than a grayscale image (8-bit depth) of the same size and resolution.
  14. 14. Bit Depth  Below is a chart that shows how many colors and bits are contained in each of the electronic color modes. The number of channels refers to the number of "plates" of color that a file contains. Color Mode Bit Depth Channels Colors Bitmap 1-Bit 1 2 tones Grayscale 8-Bit 1 256 (254 grays, black & white) RGB 24-Bit 3 (R, G and B) 16.7 million CMYK 32-Bit 4 (C, M, Y & K) 16.7 million Indexed 8-Bit 1 2-256 colors
  15. 15. Identify the various monitor resolutions and printer resolution  A monitor's resolution is the next area to be concerned with. A monitor's resolution indicates how closely packed the screen pixels are. The more pixels that you have, the sharper the image on screen and the more expensive the monitor. High end monitors display 1280 pixels by 1024 pixels and above. Low-end monitors display 640 pixels by 480 pixels.  All of these factors should be taken into consideration when purchasing a monitor and when considering if a monitor is as good a deal as it seems. Designers are encouraged to purchase the largest monitor, with the greatest resolution, that they can afford. The programs designers use come with a lot of control palettes that take up screen space. On top of that, working with color images is not really practical or possible with anything but a high-resolution monitor which features lots of pixels per inch.
  16. 16. Identify the various monitor resolutions and printer resolution  If you are going to display an image on the screen you should always use 72 dpi, unless you want to be able to resize the image.  Monitors display patterns of colored pixels. These displays are measured in pixels per inch or ppi. Web pages and multimedia projects typically use 72-96 ppi both to keep file sizes down and to display properly on small or low-resolution monitors.
  17. 17. Identify the various monitor resolutions and printer resolution  How an image appears on-screen is actually dependent on a couple of factors. The quality of the monitor being used plays an important role as does the actual image's quality. If an image is a 24-bit, RGB image with 16+ million colors, but a monitor is only able to display 16 colors, the image won't look too good no matter what. The common resolution for on-screen images (for electronic presentations and Web pages) is 72dpi. This is because 72dpi is what monitors can display. Anymore resolution than that is wasted. A higher-resolution image won't look any better on-screen but, you can be sure, the file size will be larger.
  18. 18. Identify the various monitor resolutions and printer resolution  If one is going to use images for a Web page or an on-screen presentation, it's important to understand what is not necessary for the image's best appearance. Sometimes, people make the mistake of putting image files, of the same resolution that they use in printed materials, on the Web or in presentations. As a result, the images take a long time to download from the Web and presentation programs run very slowly.  It’s wasted because an image at 72dpi will appear just as clearly and as smoothly as one that is 720dpi. The images will look the same but the one that is 720 dpi will have a much bigger file size. This bigger file size will take longer to download on the web and will significantly slow down the performance of a presentation program like PowerPoint. The presentation document will also balloon in size proportionately.
  19. 19. Identify the various monitor resolutions and printer resolution  Images used purely on-screen should be in the RGB color mode or index color which is based on RGB. Both Web pages and on-screen presentations are seen on monitors which use red, green and blue (RGB) pixels to display color on-screen so, images saved in an RGB color mode will naturally look better.  Printers apply dots of ink or toner onto paper or other media. Printed images are measured in dots per inch or dpi. Each printer has its own output image requirements. Modern desktop printers (laser or inkjet) typically print somewhere in the range from 300 to 1700 dpi.
  20. 20. Identify the various monitor resolutions and printer resolution  The smaller the print pixels, the higher the resolution setting. For instance, an image with a dpi of 150 will have smaller dots than an image set to 72 dpi. The higher the resolution, the higher quality the print out will be, up to the printer's physical capabilities.  When an image is printed, each image pixel puts out a dot of ink or toner. When an image is printed with enough dots, the human eye perceives discrete color changes as continuous, and the digital image looks like an analog photograph.
  21. 21. Identify the various monitor resolutions and printer resolution  What can be very confusing to the new Photoshop user is that an image with a low resolution can look good on the screen if not zoomed in too close. You could work away on an image believing that you have a high quality image and when you print it out be very disappointed when you see that the large size of the pixels makes the image look blocky or pixilated. It takes a higher resolution for an image to look good in print than it does on screen.  Information on printing resolution can be found in the above section on Measure on Output device resolution.

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