Need to reduce d.p.i. on Photos for Commercial Printer

[papajoe]

I'm having a problem reducing the number of pixels in gray-scale mode on my TIF Black & White graphics (obtained by scanning from color pictures). I have a HP Scan Jet IIcx, and have tried everything their Book suggests. However, I think the problem can be corrected by use of PhotoShop 5.0LE, which I received when I upgraded from PageMaker (IBM)6.0 to 6.5 version.
Can someone please walk me through this process. The graphics on my Bulletins look great when printed out by my HP Laser Jet 1100. However, when I take them to the commercial printer and they do their copy for enlargement and final processing in 9" by "12 paper format, the photos do not look the same--they have kind've a "bleached" affect.
Thanx...

 

[zefir]

The main question: how many pixels are necessary ?
Any printer works with ppi and lpi. High quality uses 1200...2400 dots per inch
and about 100 dots per raster cell. e.g. 1200 dpi, 100 lpi .
The highest professional raster frequency is 200 lpi.
Each raster cell needs 1.5 to 2 source pixels, let´s say 2.
For 5 inch image width you need 5*200*2 = 2000 pixels
Scan TrueColor 24 bit 300..600 dpi with this pixel width and
with the proportional height.
Do not use sharpeners for scanning. Apply any image processing,
especially the conversion Color to Gray (256 grays). Apply eventually
different Contrast and Sharpener. Store TIF or BMP.
Fundamental LAW: To many pixels do no harm - only the file size
is increased.
If you can´t handle such a big file during the scan, then scan half the pixel size
and blow up with PhS by interpolation (bicubic).

The scanning of rastered NEWSPAPER is much more difficult. Please refer
to URL: -----G.Hoffmann

http://www.fho-emden.de/~hoffmann/howww04d.html

 

[zefir]

Continued: PageMaker doesn´even touch your source image.
Sends only directives to the printer where to place and how to
scale the image. The actual rastering is then done by the printer
(RIP=Raster Image Processor).---G.Hoffmann

 

[zefir]

So far no reply - good occasion for a simple recipe:
Your printman tells you: I never use a higher raster frequency than 200 lpi.
You decided: My printed image width is never larger than 5 inch.
Necessary pixel width for scanning: xp = (1.5..2)*200*5 = 1500..2000 pixels.
Never scan in cm or inch sizes, always in pixel sizes.
Hope this helps -----G.Hoffmann

 

[papajoe]

Re: Problem with Commercial Printers copying my graphics for bulletins. Perhaps I failed to explain the problem correctly. It seems I have too many pixels in my Page Maker 6.5 product. When I place the "Linen Tracer" on graphics there is not enough "spread" between pixels. The printing shop folks suggest I reduce the number of dpi from 300 to 150 or 75. This is where my problem begins. I have a HP ScanJet IIcx scanner and a HP 1100 Laser jet printer. I also have Photoshop 5.0 Limited Edition that came with my PM 6.5 Upgrade.
Although I've read and reread the areas concerned in the manual, and followed the help menu in Photoshop, I still can't seem to arrive at a finished product that is compatible for reproduction at commercial printer.
Is there a way of "reducing" the number of pixels per inch through Photoshop 5.0, or through my scanner?

 

[zefir]

PapaJoe: You need simply ENOUGH pixels.
Too many pixels in the source file DO NO HARM.
What is "Linen Tracer" ? Never heard.
If you like, you can reduce the number of pixels
by PhS. Simply select Image Size and redefine
the pixel number, keeping the size in cm or inch the same.
BUT THIs IS NOT NECECESSARY FOR PAGEMAKER.
Why is the final quality not satisfying ? Please describe the appearance .
And, please, tell which printer was used for the tests.
---G.Hoffmann

 

[zefir]

PapaJoe: Please read again my third message:
this is for commercial printers.
Meet you tomorrow ... sleeping time now here
in Europe.----G.Hoffmann

 

[papajoe]

A "Linen Tracer" is a magifying device that views graphics 2.5 inches away from surface of paper. It shows the pixel spread and half-tones which will be transferred by commercial copier for newspaper-type duplication.

I have no problem with my copying technique for Web use or personal letters with photos. The problem arises when these photos have to be recopied and printed by a commercial printing firm. They insist that the half-tones are not spread apart sufficiently for good reproduction. I have viewed what they use with the Linen Tracer and the pixels and gray scale half-tones are spread twice as much as on my end-products.

It's strange that I've been able to assist so many others with Pagemaker problems in the past and offered viable solutions that really work, but this one has me stumped.
I really would appreciate some assistance from anyone who has had this problem and conquered the same.
Joe Coppinger/Perris CA

 

[zefir]

PapaJoe: it´s funny that you get good results with the desktop
printer and the commercial printer doesn´t accept your
images. "Not spread apart": does this mean: the black is dark
gray and white is light gray ? Then you can apply in PhS
"tonal correction". You will see a histogram, and if my assumption
is true, then there is a gap at the left side and the right
siden. Expand both ends until the whole range 0....255 is used
for the new image version. I apologize for not being able
to tell you the PhS menue keywords, because I am German.
Once the technical part has been made clear, then someone else
could perhaps help to lead you through the menue.
Or did you apply Rastering (it´s called "Bitmap" in PhS) ?
Then it´s a different question ! The commercial printer usually
gets the unrastered (of course pixeled) BMP or TIF files.
G.Hoffmann

 

[papajoe]

The gal that works at the commercial printing shop states that she's also having trouble making this work on her IBM copy of Pagemaker and Photoshop. However, the printing shop uses a MacIntosh version of Pagemaker and Photoshop. So--this might be something only correctible by a Max computer and Mac version of Photoshop. We'll be comparing notes in person tomorrow at the printing shop. I'll get back to you if we find a fix. Thanx for the concern and suggestions. Regrds, Joe Coppinger/Perris CA

 

[papajoe]

Just found out that the one commercial printer who use a set-up similar to that of newspapers and magazine production, requires that I use 85 lines per inch at 72 dpi, which are different instructions from their guidelines of last week. I set these adjustments via Photoshop--and there are a couple other adjustments that have to be made as well.

At the other commercial printers, who use a large copying machine for their end products, they require that I use 85 lines per inch at 300 dpi.

I hope this will take care of the two individual duplication of photo and text files.

 

[zefir]

PapaJoe: nice, you are here again.
A rough estimate for desktop printers:
1200dpi/106lpi
600 dpi/ 72lpi
300 dpi/ 50lpi.
Can´t you send the Unrastered Images to the service
Bureau, and they can handle them as they like,
provided you have ENOUGH pixels in your source ?
The text quality is of course NOT affected by the lpi-setting.
The film is usually made by an Imagesetter with very high
resolution. G.Hoffmann

 

[papajoe]

zefir (G. Hoffman):
Are you saying I shoould print my 300 dpi TIFF at 50 lpi? Should I also check the "interpolation" box on Photoshop?
Joe Coppinger/Perris CA <papajoe32@aol.com>

 

[carlow]

If I may say something about this hole discussion , it is for me not very to the point.

If your commercial printer says you have to reduce your dpi's it is a question of time spending for him.

I'll explain.
If the scanned image is not more than half the size of your placed and printed version, you should consider the lpi of your commercial printer for adjusting the file's size. If the lpi of your commercial printezr is let's say 100 lpi, and you scanned the ima at 100% and the placed image is not more than 150% of the original, you take 2.5 times the lpi's of the commercial printer and set this as your scanning dpi's.

if you take more dpi's on the image the calculating time for the commercial printer's rip is very long. But when the ripping of the image has been done the printer will get rid of all the unneccessary data because of the limited lpi's. So his machine is calculating too much data and the result will never be better than with the conditions spoken above.

Most people think that a 50 MB Photoshop document will be a better document than a 5 MB document.

The contrary is true. If you adjust the size and dpi's in Photoshop to a reasonable rate, your commercial printer will be happy, and so will you because of the gain of time.

The lpi of the printer or the ultimate factor of quality, but you must take care if you're image hasn't got a too big magnifying percentage.

Hope this helps

grillhouse