On 23 Mar 2003 00:47:03 -0800, eko...@hotmail.com (Ezra Kortz) wrote:
>Somebody please help bring me up to speed with the following questions! I will
>be enormously appreciative and return the favor of education back into the world!
>1. How does a bitmap image differ from a vector image?
A bitmap image is a description of the color for each point in the
image. It can't be scaled/resized without losing image information.
Resolution is used for two different purposes: A) The number of pixels
that determines the size, B) the DPI/PPI that defines how dense the
pixels are printed.
A vector image is a set of mathematically defined curves, lines and
color fills. Each element's position is defined on a virtual page.
All Elements (and thus the whole image) can be freely scaled without
loss of information. Screen and print output are different,
independent views on this mathematical data, adapted to the devices
Colors in vector images are calculated the moment they are transferred
to the output device (rastered, actually) in the desired size.
>2. The quality of a vector image printer output is determined by what?
Printing a vector image on a printer is a process of rasterizing. So
the chosen resolution (here resolution means device setting or
capability) and the way mixed colors are created will affect the print
output. Print size is less relevant - except for banding (see later).
>3.The quality of a bitmap image printer output is dertermined by what?
Here the relation between image pixels (=information) and printer
pixels counts. Set of dots of different inks/toners make a pixel.
Printhead DPI resolution divided by dots needed for shading = printer
DPI; also depends on print media, current best results for
1200/2400/2880/5760 DPI-Printers are arount 350-450ppi.
If the image is too small for the desired print size, the image's
pixels will become visible (e.g. print 100x100pixels on 8"x8" you will
see each of the 156 pixels that fill each square inch.
>4. What is Raster Image Processing?
All manipulations on raster images - most of PSP's functions are.
But what you seem to ask for: What is a Raster Image
The device that converts vector images in the raster images that
printing devices need for their output.
For the common desktop inkjet printer the PC is the RIP-device.
For large-scale and/or high-speed printers separate RIP-devices
(actually specialized computers with large amounts of memory) are used
that are connected to the print-engine. The purpose of this is to keep
huge amounts of printer data off the network and reduce the PC-memory
used when printing.
Example: When you print a 24"x36" image that consists of vector curves
and takes only some 10 MB as a file on your PC at a desired output
resolution of 300 dpi, the following will happen:
Assuming a four color (CMYK) printer can print in 2400 dpi it can use
an 8x8 pattern per color for shading for your 300dpi image
(2400/300=8, 8x8=256, so 256 different intensities for each color for
each pixel are possible (theory...)). This will use 8 bytes of print
data per pixel per color (8 x 4= 32 bytes per pixel).
We talked about paper 24" wide. Each square inch has 300 x 300pixels.
300 x 300 x 32bytes per pixel
= 90000x32 = 2,880,000 bytes per square inch.
24" x 36"= 864 square inches
864 x 2,880,000 = 2,488,320,000 bytes total print data.
=2,430,000 kb = 2,373 MB = 2,3 GB
Nobody wants to transfer this through a PC spool system via parallel
or USB cable to the printer.
>5. Are all display imagery pixel-based?
Today there are only very few vector based applications left (e.g.
some air traffic control terminals).
There were some vector graphic terminals (Tektronics) for wireframe
CAD but high quality raster displays became cheaper and thus the
standard. None of the vector terminals was able to show shading.
>6.Define the term Postscript. What is it and what is its application?
Some say it is a page description laguage, others say it is a
For more details see Adobe home page.
>7.What are some strengths of vector based software?
>8.What is one cause of the "banding" that sometimes occurs when vector shapes
>with graded fills are output?
If the number of different colors that are available for the fill
(either by user's choice or the system'sinability) does not allow a
smooth transfer the border between the different color shades becomes
visible. Use more colors or more striped for shading (=more
>9.What are some of the advantages of converting vector data to bitmap data
>before sending the data for output?
Printers and other raster devices do know nothing about vectors. You
need to transfer into their language which only has words for dots.
>10.When converting vector data to bitmap data, you must always answer two
>questions. What are they?
Hey - that sounds like your homework questions, you should be able to
answer this by now.
>11.What is the minimum resolution required for professional line
In 1986 the correct answer was 300dpi. Try converting into printers
raster or lines per inch system :-)
>12.How do you determine the necessary resolution required for color
Depends on purpose, media, device capabilities, price/budget...
>13.The number of possible color choices for each pixel in an image is
>14.An 8 bit color system (indexed color) has how many possible color
>choices for each pixel, and how is this number determined?
How many possible values are there for one byte?
>15. What is the best display resolution for reading text on a 19"
1600x1200 with font settings of >16pixels and antialias active.
Or get better glasses and use smaller fonts.
The question is nonsense if only the display resolution is asked for.
Readability needs to consider font size too - finer resolution and
bigger fonts are better than coarse resolution with edgy, pixelated
BTW: There are still 19" monitors designed for 800x600 pixels only and
my 28" TV monitor can't dispaly anything better than 720x576.
Keep only the first four words of the second paragraph.
>16.You have created a 6" x 8" full color illustration in Photoshop at
>300ppi in CMYK mode for a client. The client now requests a version of the
>file for Web publication that is 360 pixles wide. What steps would you
>take in Photoshop to prepare this illustration for the Web?
6 x 300 = 1800, 8 x 300 = 2400
resize accordingly, sharpen
While this is a computer image, it is already available in RGB so you
only need to save in the desired file format.
>18. A digital image is 200 x 300 pixels. If this image is 1.25" wide,
>whaat is the resolution of the image? How did you arrive at the answer?
Resolution is pixels per inch. Divide Pixels by inch.
>19. What is Bicubic resampling?
See Photoshop help.
>20. If a document in Photoshop reads 100% RGB how does this size relate
>to the size the image will appear in a Web browser?
>21.Define the terms image resolution and divise resolution (laser printer).
>What is the primary difference between the two?
>22. If you are scanning a watercolor illustration to prepare it for
>digital printing, and you will be printing the illustration and 3/5
should read: ...at 3/5 of...
>its original size, from a printer that has a resolution of 2540 dpi
>and a linescreen of 150 lpi, at what resolution should you scan the image?
Assuming that the question is "how can you avoid moir patterns
scaning an image printed as described with contents that doesn't
require sharp edges?" I would scan at 600 dpi, use gaussian blur until
the print dots disappear and then reduce to the necessary size.
In case of a real watercolor image: I don't know. Where is the size of
the watercolor illustration?
If you calculate the actual resolution difference between linescreen
of the printed image and target size and scan at ~150 dpi the result
wil be a fine demonstration for moir effects.
>22. If we change the resolution of a bitmap image from 150 dpi to 450dpi
>keeping the file size the same, and the original size of the image
>is 9" wide by 12" tall, what will the new size be?
Resolution and size are in reverse proportion. You calculate.
>23.What is the size of each halftone cell for a 1200 dpi printer set
>at 80lpi? How many gray levels are available?
>24. A PowerPoint slide is always 10' wide by 7.5" tall. You will be
>viewint the slide on a PC with a screen res of 96dpi. You are creating'a
>background illustration that you want to completely fill the PowerPoint
>slide. At what size pixels and resolution will you need to create
Another nonsense question.
Powerpoint slides are presented in different environments and even
printed. So the image size should keep the 3x4 aspect and be at least
big enough to fill the screen.
The teacher's assumption that there is any relation between those
96ppi and the image size goes bust when someone clicks on "full screen
presentation" where the assumed 960 pixel wide slide is spread over
the screen at usual 1024 or 1280 pixels width.
Where do they teach device specific presentation design? I'd like to
blacklist that university for recruiting.
>28.Now you are developing a PowerPoint presentation for a Mac with a
>Screen res of 80ppi. What will you need to do to prepar the background
>illustration in the previous question, so it will fill the slide of
>29. You are creating a bitmap illustration for a magazine cover that is
>8.5" x 11". The cover will be printed at a line screen of 133lpi. How many
>total pixels should your image consist of?
Calculate the relation LPI to pixels as A.
Calculate pixels as 8.5 x A x 11 x A
>30. What is the file size of a 4" x 5" CMYK image that is 350 ppi. Show the
4" x 350ppi x 5" x 350ppi x 4 colors is the raw image data.
File size is nonsense again without a given format to consider
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