[softwarelist] Re: Importing TIFFs into OPW

In article <4485F791.9000609@xxxxxxxx>,
   Clive Bonsall <C.Bonsall@xxxxxxxx> wrote:

> Thanks for this. Undoubtedly, I am using bigger images than I need to. 
> But I'm unsure about the optimum mode/dpi setting to use, so advice
> would be appreciated.

> For non-colour stuff, I tend to scan everything at 8bpp grayscale and
> the highest resolution (dpi) that my computer can manage, because I can
> always reduce the images to 1bpp and/or lower resolutions, as/when
> required.

> The JOB is this ... a book DTP'd using OPW, which will contain lots of
> line drawings and B&W photos.

First, I think it's important to distinguish between the two different
types of images you will be using in your book.

Lets start with the easy ones - B+W photos. These are in fact grey-scale
images and you will want these at 8bpp to give you the range of grey
tones you'd expect in a photo.

What can often cause confusion is that one person may refer to black and
white while describing a grey scale image (such as a photo), while somebody
else will take it to mean a 1bpp image. A 1bpp image is referred to as
'line art' and is ONLY black and white with no other tonal (grey)
levels. If there are other grey values in the image then it cannot be
called line art, even if the picture is drawn as lines.

> It will be sent to a commercial printer
> either as camera-ready copy or as a series of PDF files. For the line
> drawings what would be the optimum resolution -- e.g. is there anything
> to be gained by having the images at 1200dpi or even 2400dpi, or will
> 600dpi suffice?

There are some general guidelines that many people work to when
producing artwork/origination for printed mater. In reality there are
many factors that come into play when deciding on image resolutions,
such as printing method (litho, screen, digital press, di press etc).
Factors like device resolution and halftone screen frequency account for
most of the decisions. But as a general rule many designers stick to the
following:

1bpp line art at 1200 dpi

colour or grey scale images at 1.5 to 2 times the lpi halftone screen
frequency. So for most sheet-fed litho printed jobs 300 dpi is more then
sufficient.

For line art I most often use 600 dpi when being printed to our
imagesetter, for most jobs this is set at 2400 dpi and 150 lines per
inch screen frequency. There is no apparent visible gain in using 1200
dpi over 600.

And I'd use 300 dpi when setting grey scale images.

> In the process of generating a PDF, downsampling of
> images normally occurs. In Acrobat Distiller, if bicubic downsampling
> for monochrome images is set to 1200dpi (as in Distiller's press
> quality mode), is there any point starting off with an image that is
> larger than that?

No. But then that's the clue - 1bpp monochrome images don't need to be
over 1200dpi when being printed on a press.

> For information, these are the guidelines issued by CUP for a 
> publication I contributed to recently:

> "All illustrations, either as CRC (line figures), prints/transparencies
> (photographs) or as digital images.  If you're submitting the images
> digitally then they should be saved at a minimum resolution of 1200 dpi
> for line figs/300 dpi for photographs, when saved at the size at which
> they'll be reproduced in the book.  TIFF or EPS files, please."

These are the same values I've written above and are used in most print
specs. But what should be carefully noted here (and goes for all the
specs I've already written) is that these values are applicable to the
image at the size it is to be printed - i.e. when they are in the
document and scaled to the final size you require.

Ovation Pro has the very handy feature of providing the Picture info
dialogue which clearly shows the resolution, in dpi, of the image in the
frame at its current scaling - i.e. what it will be when printed.

A good method to get your final image sizes down is this:
Drop in your overly large scan into the frame and scale it to the desired
size. Look at Picture -> Info... and see what the resolution is.

Load the image into DPScan, and with the Select/pointer tool selected
enter this dpi value into the dpi writable icons and press return.

Use Edit -> Resize... and set the Resolution values to the final
required values (1200/300 depending on image type) and hey presto you
have the required image size when you load it back into OPW.
[for RISC OS/DPlngScan use Edit -> Scale, Resample]

> In this case I found that my computer (Athlon 2600+, 1GB memory)
> couldn't even manage to save 1200dpi TIFFs of some of the illustrations 
> (those that included grey tones) -- 800dpi was its limit. Yet this is 
> what many publishers are asking for.

Thats the confusion over the terminology being used. Anything with tones
only needs to be 300dpi, 1bpp line art at 1200 dpi.

One final point - avoid saving images with anti-aliasing turned on -
especially when you have areas of solid black against pure white, such
as text. It seems to be a very common mistake these days and it can turn
a nice design into an instantly poor printed job.


I'm just trying to think if I've covered everything. Probably not, so if
you are not sure just ask. Having spent over 20 years in the
prepress/print industry I find it difficult to sum up that experience
into a few paragraphs when someone asks me 'how do you want it?'.

-- 
Gavin Crawford
email: gav@xxxxxxxxxxxxxxxxxxxx
  web: www.crawford-print.co.uk

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