Hi Steve!
I am working with color images; I'm using a networked color laser printer
that is at least 600dpi (it may be 1200, but I'm not positive). I assume the
difference between 600 and 1200 would be beyond the scope of human
detection. I'd think (just a guess, I haven't tested) that the difference
between 100-200 is more easily detectable, and the difference between
200-300 detectable under certain circumstances, etc.
I hadn't thought about it, but the color laser probably must also use
interpolated dots to provide the appearance of the color range- so the more
color, the lower the 'true' resolution would be anyway. I can't help but
wonder if a 100dpi color image on a 300dpi printer is rendered in a way to
use the extra pixels for the coloring- probably not, it probably just prints
larger blocks of interpolated color... man, now I'm going to be wondering
about that all weekend. I suppose a color inkjet could overprint (resulting
in dye mixing for color rendering), but that's a whole different animal
anyway.
The good news (although with your logic, probably irrelevant) is that I
realized I could print these to pdf at 600dpi, effectively downsizing the
file. Of course, I have no idea what else the conversion might be doing to
the images (compression, etc). At least in initial tests, it seems to print
with sufficient clarity for our needs, and the file dropped from 30MB to
about 2MB- a heck of an improvement either way.
Thanks again for the logical explanation - next time I won't worry so much!
Keith
"Steve Rindsberg" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
>
> Let me make a couple educated guesses:
>
> - You're working with color or grayscale images, not pure b/w 1-bit images
> - You have a b/w laser printer rather than a color printer, probably a
> PostScript based printer.
>
> If both guesses are true, you definitely don't need 600dpi.
>
> Laser printers can't print gray; they can print black dots or not print
> black
> dots. By changing the way they print black dots, they can *fake*
> grayscale
> values but in doing that, they trade away resolution for the ability to
> produce
> so-called "halftones" (gray values). It's too complicated to go into here
> but
> the net result is that for a typical 600dpi laser printer, anything over
> about
> 150dpi is wasted, so PPT's 200dpi "Print" compression setting should do
> fine.
>
> But don't trust me. Test on your own equipment.
>
> Make three copies of one image with different filenames.
>
> Add three slides to a typical presentation you'd create.
>
> Pop one image into PPT normally (Insert, Picture from File)
>
> Pop another in and let PPT compress it to 200dpi (print setting)
>
> Externally downsample the third to 600dpi and then Insert, Picture, From
> File
> to bring it into PPT.
>
> Now print all three slides.
> Let truth be revealed. ;-)
>
> If the results are surprising in any way, c'mon back and let's talk.
>
>
>>
>> I'd rather stay with huge files than have lower than 600dpi resolution,
>> so
>> if there isn't a solution, I'll still be ok unless the printer chokes on
>> such a large file (maybe requiring printing a page or two at a time).
>>
>> Thank you!
>> Keith
>>
>
> -----------------------------------------
> Steve Rindsberg, PPT MVP
> PPT FAQ: www.pptfaq.com
> PPTools: www.pptools.com
> ================================================
>
>
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