Pixellation and dpi

[Tony Irwin]

The new pictures I've done for Shoujo Story are printing out ever so slightly pixellated. I scanned and saved the images at 300 dpi, which I understand is kind of the minimum quality you should expect to get away with?

I've got three questions and I'd be really grateful for any help anyone can give me with this. Please bear in mind that I find this stuff pretty hard to follow and you may have to define any technical terms you use...

1) I've noticed that people talk about dpi in terms of 300, 450, 600 and so on. Does it have to be a factor of 150?

2) Do I need to set the dpi of the pdf as well as the images in the document. What dpi should I set the pdf at?

3) These are black ink drawings printed on white paper. I'm planning to sell print copies only through Lulu so the size of the pdf isn't a big issue for me. Bearing all this in mind can you recommend a dpi for me to use?

Many thanks!

Tony

[Luke]

hi tony,

if you link me to a jpg sample I can give you more specific feedback, but right now, I'd make sure you're outputting your PDF at PRINT settings at minimum.

If you want to set the DPI of your PDF (which I don't recommend), you can set it to 150 DPI.

Most laser printers and inkjets print at 150 DPI (as determined by photoshop).

-L

[Ron Edwards]

Hiya,

Wincing ...

Focusing just on the scan issue: my advice is to scan at the very highest DPI that you can afford to store. I mean, really high, 1200 if you can.

You can always save new versions (and in new formats) at lower res. But believe me, when the day that must come comes, you'll kneel down and bless the day you scanned at the highest possible res.

Issues of application to print and PDF, I leave to experts like Luke and Clinton, among others.

Best,
Ron

[Matt Snyder]

Tony, one question/concern:

You say you've scanned these images at 300 dpi. That should be enough quality for almost any practical application (print, PDF, online, etc.). But, you say you're getting pixelated output.

What's the output? What kind of printer?

IMPORTANT: From what application are you printing these images. ARE THEY RESIZED in the application? (For example, maybe you "blew them up" or "resized" them on the page to, oh, 150% in InDesign -- that would account for pixelation, possibly.)

[Keith Senkowski]

To add to the barage of questions, what file format for the image did you use?  Did you prechance save it as a bitmap?

Keith

[jdagna]

Some thoughts:

1) 300 dpi is good for photos or drawings, but it's not sufficient for "line art" where everything is purely black and white (what you describe).  1200 dpi is the minimum I'd recommend for that, though you might get away with 600.  This is probably your problem.

2) If you scan at 300 dpi and then scale an image to double its scanned size, you really only have something at 150 dpi.  Never scale an image larger (unless you scan at a very high dpi to start with).  If you do scale it, never do it in your page layout program - you're almost always better off doing it in a dedicated graphics app.

3) PDF generators have output settings that can downsample some or all of your pictures, especially if you're using presets for web viewing.  Either tell your generator not to downsample at all, or set it really high (a high setting will not increase the memory of lower quality images).  If you have a specific printer, they'll often give you directions on what settings to use.

4) You should make sure to use an appropriate image type, and in this case I would only recommend TIF.  JPG formats can create compression artifacts (especially on sharp edges with high contrast) and that often looks like pixellation.  GIF images may dither (alternate colors of pixels to mimic a third color) which can look pixellated.

5) Make sure you scan the image in b/w mode, not color or grayscale.  You'll get sharper lines.  It doesn't sound like this is your problem, though.  As mentioned, do the scanning at very high quality - 1200 dpi for a b/w image is about the same file size as a 150 dpi color image anyway.

As a general answer to your questions about dpi, 150 point increments are common just to keep math simple, but monitors use 72 or 96 dpi, faxes are 200 dpi and many inkjet printers use multiples of 144 (especially 620, 1440 and 2880 in the newer ones).  However, actual printing presses and laser printers usually use 300 dpi increments (300 is a typical low end nowadays, with 600, 1200 and 2400 common) and so most layout pros tend to think in multiples or fractions of 300 dpi.

[Veritas Games]

Depending on what you are scanning in, the following trick may destroy the image, or it may vastly improve it.  For comic book images, it vastly improves it.

Blur the image with a Gaussian Blur at a 2 pixel range.

Then apply an Unsharp mask.

Comic book images are pixelated.  This type of technique can remove pixealation, at the cost of a little blurring.

[Angaros]

The new pictures I've done for Shoujo Story are printing out ever so slightly pixellated. I scanned and saved the images at 300 dpi, which I understand is kind of the minimum quality you should expect to get away with?

I've got three questions and I'd be really grateful for any help anyone can give me with this. Please bear in mind that I find this stuff pretty hard to follow and you may have to define any technical terms you use...

First off, listen to the Dagna. It sounds like he knows what he's talking about. But I'll still try to answer some of your questions.

2) Do I need to set the dpi of the pdf as well as the images in the document. What dpi should I set the pdf at?

A document created via Acrobat Distiller or by printing to "Adobe PDF" from another application will be made in a specific resolution. The Standard settings in Distiller has the document Resolution set at 600 dpi. If you, during the printing process, switch to the Press settings instead, the document will be printed at 2400 dpi. The document resolution really doesn't affect much else than gradients and other elements dependant on a resolution when calculated. Fonts are described as curves and images are generally of a lower resolution than that. If you need to specify this yourself, set it at 2400 or 1200 dpi.

3) These are black ink drawings printed on white paper. I'm planning to sell print copies only through Lulu so the size of the pdf isn't a big issue for me. Bearing all this in mind can you recommend a dpi for me to use?

As Justin said, scan the images in b/w mode (monochrome black and white if you will) in as high resolution as your scanner allows. Pure b/w images compress very well so size might not present much of a problem. It is VITAL though that you scan the images at 1200 dpi or preferrably higher. This is because of the b/w method which for each scanned pixel decides if it's gonna be black or white. No grayscales, no tones only black dots on white. If b/w images are scanned in too low a resolution you will get jagged lines and edges as a result.

- - -

A note on image resolution. What really determines how high resolution you need in your images is the halftone screen resolution of the printer used. The screen is usually described in lpi (lines per inch) and describes how many halftone cells the printer uses per inch. When printing, the printer only has two choices at any given point: drop ink/toner or don't. So, even if the printer can put out 2400x2400 dots per square inch it needs to use several of the avaliable dots to represent one shaded image pixel. Depending on the halftone method used, it either varies the size of the dot clusters or the number of dots used in each "cell" to represent a shade.

Common lpi values are: ~55 for office lasers and inkjets, ~85-120 for newspapers and magazines, ~133-150 for offset printers, ~1200-2400 for really high quality photo printers. A rule of thumb is to double the printer's lpi to get the appropriate image resolution (dpi). So for an office laser, 110-150 dpi would be quite sufficient. For printed matter, 266-300 is what you need. If reproduction accuracy is really important, then it might pay off to find out the exact lpi of the machines used at your print shop. But using 300 dpi images is usually a very safe bet. I would like to add though that a properly processed and well-prepared image of 150 dpi can look a whole lot better than a poorly processed and prepared 300 dpi image. Mucking around in Photoshop and using proper icc (color) profiles often pay off in the end. At least if you're printing in color.

[MatrixGamer]

Tony

I took a desk top publishing class last fall and they recommending 300dpi for grey scale pictures but 1000dpi for line art. The class was taught by a woman with 20 years experience in book design so I think the information is good.

When I scane pictures I shoot for around 400kb  for a 2x3 inch pic. The higher the resolution the slower the printing but the less chance of pixilation. Since your not doing the printing yourself, why not go for a higher rez?

Chris Engle
Hamster Press

[Chris Passeno]

Edit:: a lot of this is touch upon by Angaros.  I'll just agree with what he said.

Like most things in life, there are a dozen equally viable ways of doing something.

The way you scan something is determined by they type of scanner technology you are using.  For instance, if you are using a drum scanner, it's perfectly fine to scan color or greyscale images at 266 or 300 dpi.  Most lineart would scan at max 400-600 dpi.

Most of us have flatbed scanners though, which are entirely a different animal.  Each brand has its own idiosyncracies.

As a standing rule of thumb, you wanna scan things in at twice the lpi (Lines Per Inch) that your printer will be outputing at.  So if you are printing at 150lpi, you'd can at 300 dpi.  If they are printing at 200 lpi, then scan at 400.  The whole "scan as high as you can" fallacy came into being cause in the old days, scanners weren't very good, so you'd need to make up for that by scanning at the higher resolution.

Most consumer level scanners won't scan higher than 600 dpi, but they will give you the option to scan higher, by using interpolation.  This basically means that the scanner will use algorithms to guess at what it should look like at 1200, 2400, or 4800 dpi.

By the way, those resolutions are there cause of the old school linotype imagesetter machines.  Those are the negative makers for metal plate production in layman's terms.  Those Linotype machines were set for a much tighter and cleaner dot, i.e. 1225 dpi and 2450 dpi.

Now with the age of POD and Desktop Printing, there is very little reason to scan in at super high resolutions.  Most of the printing machines won't print higher than a 200 lpi.  If you are going the Traditional Route, it's an entirely different game and the higher dpi can factor in.

All the larger resolutions will do is to create a file with a bigger footprint and contain no more printable data than a smaller one.

Seriously, if you have questions, ask your printer.  They usually have a spec sheet on how to set up files for them.

Of course, this is only part of the issue.  As others have stated, once the file is set up correctly, you still need to make the pdf correctly.  Many people have the misconception that you click a button and you have the miracle PDF that will solve world hunger.  There are many joboptions in Distiller that will effect how the pdf turns out.  Again, ask your printer.

You'll find that everyone has an opinion on scanning stuff.  It's their tried and true, never fail method.  Great.  If it works for them, they use it.  But keep in mind that it's just like the PC vs. MAC argument or the Quark vs. Indesign agruement.  It's all opinions until your printer speaks up.

[Angaros]

As a standing rule of thumb, you wanna scan things in at twice the lpi (Lines Per Inch) that your printer will be outputing at.  So if you are printing at 150lpi, you'd can at 300 dpi.  If they are printing at 200 lpi, then scan at 400.  The whole "scan as high as you can" fallacy came into being cause in the old days, scanners weren't very good, so you'd need to make up for that by scanning at the higher resolution.

Just make sure you don't confuse the printer's dpi with it's screen lpi. Most technical detail sheets only specify the printing resolution (in dpi) but never mentions the halftone screen resolution (which is noted in lpi). But as Chris said, printers have usually gotten fed up with bad material from customers and created a document with guidelines for the customers to follow. All printers I've worked with have had such docs. Very handy. And they usually welcome questions since it means less hassle for them in the end anyway. :)

[Tony Irwin]

What a fantastic site this is, thanks so much to everyone who replied.

You've all given me lots to go on, and from that I can already see several things that I've been doing completely wrong.

Thanks again to everyone who replied.

Tony