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Premedia II - Midterm Review Sheet.pdf

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Graphic Communications
GRA 423
Natalia L

Premedia  II  -­‐  Midterm  Review  Sheet   Image  Assembly     Ø Image  assembly:  refers  to  placing  the  images  (pages)  to  be  printed  in  the   correct  position     Ø There  are  several  reasons  why  image  assembly  is  important.  For  example:   • It  ensures  a  correlation  between  the  image  area  on  plate  and  the  position  of   the  paper   • It  can  maximize  the  printable  area  of  the  paper   • It  enables  multi-­‐page  jobs  to  be  properly  imposed     Ø A  standard  offset  press  sheet  is  usually  wider  than  it  is  tall  (landscape).     Ø Not  all  of  the  sheet  can  be  printed  on.  The  area  that  can  be  printed  on  is   called  the  maximum  imageable  area.   • Any  areas  outside  of  the  maximum  imageable  area  should  not  have   ink  in  them   Ø Not  all  of  the  maximum  imageable  area  can  be  allocated  to  the  finished  print   job.     • Allowances  must  be  made  for  such  things  as  margins,  gutters,  quality   control  bars,  register  marks,  sheet  identifiers,  paper  gripper  and  so   on.     Ø During  sheetfed  offset  printing,  the  lead  edge  of  the  paper  is  physically   grabbed  and  pulled  through  the  press  by  paper  grippers.  There  cannot  be   any  image  area  in  this  space.     Plates:   • For  commercial  offset  printing,  each  printing  plate  has  a  bend  applied  to  it.     • This  allows  the  plate  to  be  securely  fastened  to  the  plate  cylinder.     • When  assembling  images  for  press,  an  allowance  called  a  plate  gripper  is   applied  to  compensate  for  this  bend.     Maximizing  the  Press  Sheet     When  running  a  job  on  press,  it  is  always  desirable  to  use  as  much  of  the  press  sheet   as  possible,  with  the  least  amount  of  waste.  Why?   • Paper  is  the  most  costly  consumable  in  printing.  Maximizing     press  sheets  keeps     costs  down  and     shortens  press  runs.   • Press  run  time  is  reduced       EXAMPLE:     An  8.5  x  11  plus  bleed  4/0  flyer  is  to  be  run  on  a  Heidelberg  sheetfed  offset  press   with  a  ½  paper  gripper  and  a  1½  inch  plate  gripper.  The  sheet  size  for  the  job  is  19   X  25.   In  order  to  maximize  the  job  for  the  paper  used,  we  need  to  calculate:     • How  many  flyers  we  can  get  on  one  sheet,  page  orientation,   and  head  orientation   • Any  job  allowances  such  as  bleed  and  gutters   • The  minimum  and  maximum  sheet  size   • Sheet  marks,  bars  and  indicators       Max  Sheet:  19  X  25   • Head  Position   Min  Sheet  18.5  X  22.5   • Dimensions     • Trims   Some  things  to  include  in  the  layout:   • Minimum  and  maximum   • Plate  Gripper   sheet  size   • Paper  Gripper     • QC  BAR   Note  that  plate  gripper  is  not   • Gripper  edge  indication   part  of  min  or  max  sheet   • Side  Guide  edge   size! indication   Pre-­‐Electronic  Image  Assembly:     Ø Before  Destop  Publishing  (DTP),  Imagesetters,  and  Computer  To  Plate   (CTP)output,  image  assembly  was  done  by  film  strippers.   -­‐  The  film  strippers  would  mount  individual  pages  of  film  onto  clear  mylar   carriers  in  the  correct  position  for  printing.  This  was  called  patching  for   press.     Ø When  patching  multiple  pages  to  a  flat,  a  process  called  checker  boarding   was  done  to  avoid  cutting  the  film  too  close  to  the  trim     Ø Premedia  operators  use  imposition  programs  like  Kodak  Preps  to  do  the   work  once  done  by  film  strippers.     Ø QC  BAR  –  COLOUR  BAR  >  Used  to  control  variability  on  press     Some  common  imposition  related  terms:   • Paper  Gripper   • Allowance  for  the  paper  grippers  on  press   • No  printing  in  paper  gripper   • Press/Plate  Gripper   • Allowance  for  the  part  of  the  plate  that  bends  and  is  fastened  to   the  printing  cylinder   • The  plate  gripper  and  paper  gripper  combined  give  a   measurement  for  plate  edge  to  first  trim   • Lead  Edge/Trail  Edge   • Lead  edge  is  the  edge  of  the  sheet  that  enters  the  press  first   (gripper).  The  trail  edge  is  the  other  end.  Registration  is  tighter   on  the  lead  edge   • Side  Guide   • The  mechanical  guide  that  aligns  the  side  edge  of  a  press  sheet   • Registration  marks   • Printing  marks  that  help  determine  register  between  printing   units/colours   • Gutter   • The  distance  between  two  trim  marks   • Spine   • The  edge  of  a  signature  that  will  be  bound.  Usually  the  spine   edge  is  a  fold,  not  a  cut  when  finishing                 Quick  Image  Assembly  Review  Questions  &  answers     The most costly consumable in printing. Paper Placing an image to be printed in the correct position in relation to the printing plate and printed sheet. Image Assembly The plate and paper gripper are both important parts of planning a plate imposition. How do these distances relate to the sheet of paper? The plate gripper is not part of the sheet When film strippers would mount individual pages of film onto clear mylar carriers in correct position for printing. Patching for Press   Before DTP the number of exposures typically needed to create a plate. Three • One  for  the  crop  marks,  registration  marks,  and  QC  Bar   • One  for  the  first  checker  board   • One  for  the  second  checkerboard                                       Resolution     Pixels  per  Inch  (ppi):   • Refers  to  the  number  of  pixels  per  inch  in  a  digital  image   • ppi    and  dpi  are  often  used  interchangeably  but  strictly  speaking  this   is  not  accurate   • The  total  number  of  pixels  in  an  image  can  be  calculated  by   multiplying  the  height  and  width  of  an  image  by  the  ppi.   • E.g.  an  8  x  8  image  at  300  ppi  has  5,760,000  pixels   (8  x  300  x  8  x  300)   Dots  per  Inch  (dpi):   • Dots  per  inch  generally  refers  to  the  number  of  dots  per  inch  used  by   an  output  device  to  image  a  file.     • dpi  is  not  affected  by  ppi  –  a  300  dpi  printer  can  be  used  to  output   both  a  300  ppi  file  and  a  72  ppi  file.   • High  quality  output  usually  has  a  dpi  that  is  greater  than  the  ppi.  This   results  in  better  tonal  quality  because  multiple  dots  can  be  used  to   define  each  pixel.   • If  my  printer  has  a  resolution  of  1200  dpi,  and  my  image  has  a   resolution  of  300  ppi,  then  the  printer  is  using  4  dots  to  define  each   pixel.  At  2400  dpi,  there  would  be  8  dots  to  define  each  pixel.   (1200/300=4)     Input/scan  resolution:   • The  amount  of  pixel  information  that  has  to  be  captured  by  an  input   device  to  obtain  the  correct  output  resolution  at  final  print  size   • This  is  always  2  x  LPI  x  Scale  Factor  (or  R%)     • E.g.  a  4  x  4  original  would  have  to  be  scanned  at  600  ppi  to  get  an  8  x  8   image  at  300  ppi   • 4  x  4  x  600  x  600  =  5,760,000  =  8  x  8  x  300  x  300   • R/O=R%  à  8/4=2  or  200%   • 2  x  150  x  2  =  600  ppi       Output  resolution  and  effective  resolution:   • Output  resolution  is  what  you  want  the  final  image  to  be  a  print  size   • This  is  always  2  x  LPI   • Effective    resolution  is  a  term  that  factors  image  scaling  done  in  a   layout  program   • A  300  ppi  image  placed  in  InDesign  at  200%  would  have  an   effective  resolution  of  150ppi     Device  resolution:   • Device  resolution  is  the  number  of  dots  per  inch  an  output  device   images  at   • Device  resolution  and  dpi  are  really  the  same  thing,  but  dpi  is  often   used  incorrectly  to  refer  to  image  resolution,  so  the  term  device   resolution  can  be  used  to  differentiate     Line  Screen  Ruling     Ø Line  screen  ruling  is  the  resolution  of  the  final  printed  pattern.  It  is  measured   in  lines  per  inch  (lpi).   Ø A  2400  dpi  platesetter  uses  16  laser  dots  to  create  one  printing  dot  when   outputting  a  150  lpi  plate  2400/150  =16     AM  Versus  FM   • Amplitude  Modulated  (conventional  screening)  uses  varying  sized   dots  equally  spaced  apart  to  create  the  illusion  of  continuous  tone   (e.g.  150  lpi)   • Frequency  Modulated  (stochastic)  screening  uses  equal  sized  dots  in  a   random  scatter  pattern  to  create  the  illusion  of  continuous  tone  (e.g.   10  micron)   • No  line  screen,  finer  detail,  no  moiré     AM   FM   Advantages   - Lower  dot  gain   -­‐  No  moiré  or  rosette  patterns   - Good  wear  on  the  plate   -­‐  Finer  image  detail   - Can  be  used  with  conventional  film   -­‐  Sharper  image   Disadvantages   - Less  detail   - Need  CTP   - Have  to  worry  about  dot  shape  and  angles     - Controlled  environment  (must  be  clean)   - Difficult  to  maintain  highlights   - Can  take  longer  to  RIP     Characterizing  plates     -­‐  There  are  several  ways  you  can  divide  all  of  your  plate  options   • Conventional  or  CTP   • Metal  or  Plastic   • Thermal  or  violet  diode   •  Processed  or  processless     Conventional  Litho  Plates     • Conventional  plates  are  exposed  from  negatives  or  positives  via  high   intensity  light  sources   • Conventional  plates  are  classified  as  either  negative  or  positive  working,  and   additive  or  subtractive  processing.     Negative  Working  Plates  (~90%  of  the  Canadian  market)   • Light  adds  image  area  (Exposure  Trait)   • Advantages:   • Less  dust/dirt  problems   • Less  complex  processing   Positive  Working  Plates  (Europe)   • Light  removes  printable  coating   • Advantages:   • Bake  =  run  length  extension   • Sharper,  less  dot  gain   Additive  Processing   • Image  reinforced  with  lacquer  during  development  (positive  plates)   Subtractive  Processing   • Non-­‐image  removed  during  development  (negative  plates)   Most  are  sensitive  to  Blue  &  UV  light     • Handled  under  Yellow  Safelights  &  require  exposures  of  approx  1  minute  to   5000W     Digitally  Exposed  (CtP)  Plates     -­‐  There  are  several  different  offset  plate  technologies  used  on  the  market  today.   • The  technologies  used  refer  to  the  coatings/processes  used  to  create   an  image  and  non-­‐image  area.   • Different  technologies  result  in  different  quality  (cost  vs.  quality)   -­‐  These  plates  are  exposed  via  a  laser  from  digital  files  -­‐  no  film  is  required.               Plastic     Silver  or  Polymer  Emulsions  on  Plastic  Substrates   • Run  lengths  under  25,000   • Single  or  spot  colour  work  only   • Questionable  for  process  work  due  to  dimensional  stability  (plastic   stretches)   • Some  are  conventionally  processed   • Developer,  fix,  wash,  dry   • Some  are  based  on  "dry  processing"  systems   • Polaroid  -­‐  Donor  Transfer   • Pearltek  -­‐  Vacuum  non-­‐image  area  (Heidelberg  DI)     Metal     Silver  or  Polymer  Emulsions  on  Aluminum   • Run  lengths  100,000  to  1,000,000   • Early  emulsions  had  exposure  consistency  issues,  and  a  max  LPI  of   175  (e.g.  Hoescht  N90)   • Today,  emulsions  are  improved  (Silver  Halide)  or   Silver/Polymer  emulsion   • Good  resolutions  and  run  lengths   • Advantages   • choice  of  a  variety  of  lasers   • visible  light  (including  newer  “Violet  sensitive”  CtP  plates   employing  lower  cost  Violet  Lasers),     • expose  both  film  and  plates     Thermal  vs.  Violet     • Thermal  technology  dominates  the  8pp  and  larger-­‐format  categories     • Multiple  beams  of  light   • External  drum  CtP  systems   • Owns  75%  of  plate  market   • Violet  CTP  is  key  in  smaller  format  installations  and  newspapers   • Single  beam  of  light   • Internal  or  flatbed  CtP  systems   • Thermal  needs  more  power  than  violet                   Thermal     Thermal  CtP  Plates  (standard  for  Litho  CtP  today)   • Advantages   • Run  lengths  2,000,000  plus   • Exposed  with  non-­‐visible  light,  so  it  can  be  handled  under   normal  room  light  conditions     • Stable  exposure  from  infrared  laser  (heat  threshold  vs.  light)   • Extremely  high  resolution  (Hard  to  spill  over  exposure)   • Disadvantages     • Conversion  to  thermal  necessary  -­‐  if  retrofitting  an  existing   imagesetter  -­‐  cannot  image  film  after  (special  laser  head)   • Cost  can  be  2x  conventional  plates   • This  is  coming  down     Plate  Making     • Generally  a  plate  is  coated  with  a  light  or  heat  sensitive  emulsion  layer   • Then  through  a  process  of  lasers  exposing  the  plate  a  latent  image  is   left  behind     Thermal  (CtP)  Plate  Making       Process  and  Processless  Plates     Processless  Plates   • Generally  shorter
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