The Datafile PD-CD 5/DATAFILE_PDCD5.iso/utilities/c/cfsiscale/!CFSIscale/!HelpFile/HelpFile

Text File | 1993-08-21 | 10.6 KB | 217 lines

!CFSIscale

       With thanks to Data Store for their 'on-line help' code

 Help on the use of !CFSIscale v.1.30 - © M R Davies - December 1992
 ===================================================================

  1. Introduction
  ===============

  In order to obtain the best results when printing images from the
screen, and bit-images (Sprites) in particular, it is important that
as much information as possible is preserved from the original image
within the image to be sent to the printer and that its x-y pixel
resolution should match that of the printer to be used, on a 1:1
basis, - taking into account the final desired size of the printed
image.

  Since many images to be sent to a printer will be of a different
size and/or aspect ratio to the original and with varying x-y pixel
counts, the need for accurate scaling prior to printing is
essential.

  If less than optimal scaling is used then there is a risk that
information will be lost and/or that interference patterns may be
introduced - especially when dealing with scanned and digitised
images. The printer should not have to do any scaling on its own
account for optimal results and this is especially evident when
attempting to get the best results from colour printers such as the
HP500C or PaintJet.

  The notes accompanying Acorn's "!ChangeFSI" cover these points as,
in more detail, do those recently released with the updated RISC-OS
3.xx Printer Drivers covering the use of "!ChangeFSI". An extract
from the latter ( © Acorn ) is appended to these brief Help notes.

  Whilst the calculation of the appropriate factors to be
incorporated in "!ChangeFSI" is a straightforward mathematical
exercise, it is a tedious one to have to perform each time a new
sprite or print size etc. is required. With this in mind, this small
application was developed to enable any values for printer x + y
resolutions, together with a required print width, height or both
width and height, to be used to quickly calculate the scaling
factors required by ChangeFSI.

  It should be noted incidentally that the example calculation used
in the Acorn notes, referred to above, could be misleading since it
does not reproduce the input sprite's aspect ratio in the calculated
printout. This corresponds to choosing values (possibly without
regard to the sprite's aspect ratio) for both width AND height in
"!CFSIscale" rather than just width OR height which will preserve
the original aspect ratio of the input sprite in the printout and
might be the more usual printing requirement.

  2. Operation of "!CFSIscale"
  ============================

  1.  Double click on the application to mount on the icon bar in
  the usual way.

  2.  A standard info box opens on clicking MENU over the icon bar
  and contains the usual Info, Help (this file) and Quit options.

  3.  Click SELECT over the icon bar to open the "!CFSIscale"
  window. This can be moved, sent to the back or front or closed in
  the normal way.

  4.  Click SELECT over (a) the desired printer resolution (300x300
  dpi is the default): (b) the desired final print dimension(s) to be
  entered - Width only, Height only or both Width + Height ("Width
  only" is the default) - and: (c) the desired units (inches or cms).
  Any other boxes will then be de-selected.

  5.  Enter + <RETURN> the desired printer resolutions (if "Other"
  has been selected) followed by the required final print dimension(s)
  in inches/cms + <RETURN> and the input sprite's X- and Y- pixels +
  <RETURN>. The "CALC" box may also be clicked at any time.

  6.  Values to be entered in "!ChangeFSI"'s scaling boxes will then
  be calculated. These can be picked up from "!CFSIscale" and
  transferred to "!ChangeFSI" using a utility such as !Transfer from
  Apricote Studios or entered by hand. Input variables and printer
  resolutions may be changed at any time and succesive strokes of
  <RETURN> or a click on the "CALC" box will re-calculate the new
  scaling factors.

  7.  The cursor may be moved around the window's boxes in a
  sensible fashion by the use of the cursor keys as well as the mouse
  pointer and most "silly" entries will throw up an error and ask for
  new values to be re-entered.

  N.B.  Do not forget that images from both !Paint and !Draw print
  out at 90 dpi from the screen. Printing scales for X- and Y- axes
  should therefore be adjusted by a ratio of 90 : X- or Y- printer dpi
  in !Paint, or scaled within !Draw by the appropriate factor(s),
  before printing. If this is not done the resultant printout will be
  of the wrong size!
  Example : If printer resolution is 300x300 dpi then scaling in
  !Paint's print box is 90:300 and the scaling or "magnification"
  factor for the image in !Draw, before printing, is 0.30 (90/300 =
  0.30).

  3. Extract from Acorn's release notes with RISC-OS 3.xx !Printers
  =================================================================

 " Using !ChangeFSI for colour bit image printouts.
   ------------------------------------------------
  The colour matching of the printer drivers is not always quite what
it could be, and how good it is varies depending on the image being
printed. If you are printing bit images (ie. sprites) to colour dot
matrix pinters, an alternative is to use !ChangeFSI on the Support
disc. This tends to give better colour matching (it is certainly
different and vision is very subjective) and it gives you more
control. Doing this requires care to ensure that !ChangeFSI and the
printer drivers do not fight with each other. It also requires lots
of memory for large images eg. you will need 8MB of memory to print
full A4 at 360 by 360 DPI, and to print full size A3 at 360 by 360
DPI 16MB of memory is just about enough. Obviously lower resolutions
and smaller output sizes will take less memory eg. 180 by 180 DPI
full size A4 can be printed on a 2MB system and 180 by 180 DPI full
size A3 can be printed on a 4MB system. Halving the resolution
divides the amount of memory needed by four.

  There are two very important steps. The first is to set the "Output"
window of !ChangeFSI to "Mode" 27 (or 31 ie. 4 bits per pixel,
square pixels), "Use current mode" off, "Ignore pixel aspect" off,
and select "Special:" and enter "D" in the special box. For the
technically minded this tells !ChangeFSI to produce output in terms
of 1 bit of each of red, green and blue ie. saturated colours. There
is an exact mapping from this to the CMYK (Cyan, Magenta, Yellow and
Key black) colour space used by the printer drivers and hence they
can accurately print the output from !ChangeFSI.

  The other important step is to get the output from !ChangeFSI to be
exactly the pixels that will be printed on the paper, so that the
printer drivers do no scaling. You will use !Paint to print the
output from !ChangeFSI, and in !Paint there are 90 dots to the inch
(90 DPI). So for example if you are printing to a 9 pin colour
ribbon printer at 120 by 72 DPI, you need to set the "Scale x" to
90:120 and the "Scale y" to 90:72 in the !Paint print dialogue box.
For a 24 pin printer at 180 by 180 DPI it would be 90:180 and
90:180, and for the Canon BJC-800 bubblejet printer at 360 by 360
DPI it would be 90:360 and 90:360. Obviously to be able to do this
the image needs to have been scaled correctly in !ChangeFSI
otherwise it will be the wrong size, and will be distorted on a 9
pin printer.

  To get the scaling correct in !ChangeFSI, you need to look at how
big in pixels your source image is, work out how many printer pixels
you want to turn that into, and scale it appropriately. It is worth
scaling something up in size, particularly if there are a lot of
colours in the original (eg. a 24 bit master) as this will give
!ChangeFSI more pixels to play with in the error diffusion and hence
the colour matching will be better. For example you have a 24 bit
master image which is 1384 by 1760 pixels in size. You are going to
print this on A4 paper to a 9 pin printer at 120 by 72 DPI. A4 is
8.269 by 11.694 inches. To cater for the fact that the printer can't
print to edges of the paper, knock 10% off which gives 7.517 by
10.631 inches. Multiplying those sizes by the 120 by 72 DPI
resolution gives 902 by 765 pixels required as the output sprite
size. In the "Scaling" window of !ChangeFSI, set "Ignore pixel size"
to off and select "Custom" scaling. The top size (for horizontal or
X scale) should be set to 902:1384 and the bottom size set to
765:1760. You may select either (or both) of "Mirror L/R" and
"Mirror U/D" without affecting anything else, but if you select
"Rotate" you will have to think carefully about the affect this will
have on the pixel sizes. Print it straight first and then experiment
later.

  The only other thing you need to do is apply whatever "Processing"
you want in !ChangeFSI. It has been found that on 24 pin colour
ribbon printers and high resolution inkjet printers (eg. Star
LC24-200 at 180 by 180 DPI and Canon BJC-800 at 360 by 360 DPI)
"Gamma correction" turned on and set to 3.0 works quite well. For a
9 pin colour ribbon printer (eg. Citizen Swift 9 at 120 by 72 DPI)
the gamma correction needs to be less; around 1.6 to 2.0 works well.
To lighten the image increase the gamma correction and to darken it
decrease it. Changing it in increments of about 0.4 seems to get the
right balance between changing too quickly or too slowly.

  You are unlikely to need any of the other "Processing" options
unless there is something actually wrong with the original image
which needs correcting, in which case it would also need correcting
even if you were going to just use the printer drivers to do all the
work instead of using !ChangeFSI.

  Set the printer drivers up to be the highest colour resolution you
have enough memory for eg. 120 by 72 for 9 pin printers and 180 by
180 for 24 pin printers. You may use either "Colour, small halftone"
or "Colour, dithered" for the "Quality:" field. In practice it has
been found that "Colour, dithered" tends to give more pleasing
results particularly at higher resolutions as it tends to smooth out
the graininess introduced by using "Special:" of "D" in !ChangeFSI.
You should try both and see which you prefer. "Colour, dithered"
takes longer and needs more memory however. "

                        ==========================

  4. Final note
  =============

  I hope that you find the use of optimal scaling gives the
  improvement in printer output that I have found and that this
  application removes some of the tedious pencil + paper arithmetic
  used in the calculations.

  All comments, queries and details of your experiences would be
  welcomed - especially from HP500C users.

  Malcolm Davies
  Marebrook Cottage
  Newborough
  Burton on Trent
  Staffs  DE13 8SP         Tel / Fax: [phone]

  December 1992