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Common Printer Myths Explained - PPI vs DPI


joshwa e2
4 710 United Kingdom
6 Jul 2011 9:33AM
A while ago someone suggested we should put together an article to explain the difference between PPI (pixels per inch) and DPI (dots per inch), and how to set the optimum printer settings for the best prints... we contact Mike MacNamee, a printer expert, and he's put together this article on the subject:

http://www.ephotozine.com/article/common-printer-myths-explained-16876

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Big Bri e2
13 15.7k United Kingdom
6 Jul 2011 9:47AM
Nice article. I presented a similar topic to my camera club last year (only had one member fall asleep), so I might link them to this, as it explains things better than I did Smile
cameracat e2
11 8.6k 61 Norfolk Island
6 Jul 2011 9:55AM
LOL.....Chris_L will be pleased......Smile

Odds on we still get forum questions on the subject.

Wink
User_Removed 5 4.6k 1 Scotland
6 Jul 2011 7:27PM
This is a prime example of how someone, purporting to be an "expert", can publish nonsense on the internet and, probably for years afterwards, have ignoramuses quoting him as "an authority"

The very first sentence in the article is pure ***** - "Images are made from pixels.". What a load of garbage.

The only images that are "made from pixels" are those viewed on a computer monitor or television screen. Printed images may be made of ink dots or of continuous tones. Painted images are made up of brushstrokes of paint. Photographic images consist of particles of silver halide.

How can we stop rubbish like this being published on our site?

(Edited to remove the foulest, but totally justified, expletives)


.
Big Bri e2
13 15.7k United Kingdom
6 Jul 2011 7:35PM

Quote:Printed images may be made of ink dots or of continuous tones


continuous tone printing just means that each pixel can be printed at any colour, rather than having to be simulated by a pattern of dots from a fixed number of colours. They are still pixels. Digital images are made from pixels. Those pixels may be printed. It was an article about printing digital images on inkjets. Duh.
strawman e2
11 22.0k 16 United Kingdom
6 Jul 2011 7:37PM
If you add one word it all makes sense and its not as bad as reported.

"Images are made from pixels.". could be "Digital images are made from pixels.". After all a print is no longer digital it is a print.

And if you read the article you can see where the author is coming from.

And to be even fairer if you put in the title from the very line above
For pixels, the simplified version runs something like this:

The context was set so I view the challenge was wrong and the author has not deviated so they gain a point and retain the subject.
Big Bri e2
13 15.7k United Kingdom
6 Jul 2011 7:41PM
LOL @ JOhn
User_Removed 5 4.6k 1 Scotland
6 Jul 2011 11:13PM
I take your point, but the general worry about unaccredited "experts" talking rubbish on internet sites still applies.

If only writers would use phrases like "in my opinion" or "my view is" or "I may be wrong, but..." then their contributions could be regarded as lay opinions contributed to a low-level discussion. The problem arises when they present garbage as fact and some folk might believe them.

I have both an MSc and a PhD but I would never claim to be an expert in anything other than the very narrow fields of my research (which are only marginally related to photography and, in any case, are probably 40 years out of date). The people writing those articles need to understand that their readers are possibly even less well versed in the science than they are and, therefore, are not in a position to recognise the flaws in what they are reading. It is amazing how much unwarranted credibility the simple process of publication bestows upon an article.
User_Removed 10 3.3k 4 United Kingdom
6 Jul 2011 11:28PM
is pleased!
User_Removed 10 3.3k 4 United Kingdom
6 Jul 2011 11:39PM

Quote:the general worry about unaccredited "experts" talking rubbish on internet sites still applies.


Lol LF it was only a few weeks ago [ here ] that you told somebody they needed to set their images to 72 ppi before uploading. "72 is the best. Any more just increases file size for no benefit when viewed on a monitor." which is, to use your word, RUBBISH
mikehit e2
5 7.1k 11 United Kingdom
7 Jul 2011 9:16AM
On the first table is the following:


Quote:

here is a simple table which defines how big your file should be
Print Size 6x4 in
Size in MB 2.2
Pixel Count
width 1080 height 720



Doesn't that go against the very aim of the article? I can have an image 3,600 pixels by 2,700 pixels and I can print that at any size I want - the program convert the (screen) pixels to (printer) dots t a ration of 1:1 or 5:1 or a gazzillion:1 to create the print size or the resolution I define. So to say that an image 1080x720 will give a print 6x4 is misleading. Do you mean that is the maximum print size you will get to have a half-decent image? If I have misunderstood then the explanation is not clear.
User_Removed 10 3.3k 4 United Kingdom
7 Jul 2011 10:58AM
Just above that it says "this is how big your file should be to produce a half-decent print". It's perfectly correct if you had an image from a camerphone and it was 1080 x 720 you could expect to print it at 6x4 but you wouldn't get good results at 20" x 16" as you need more pixels (which the camera hasn't produced).

You say "I can have an image 3,600 pixels by 2,700 pixels and I can print that at any size I want", yes but article is talking about minimum sizes for a half-decent print so of course you can print your 3,600 x 2,700 image really small but if you print it at 144 inches x 108 inches you wouldn't get good results. You'd either have fake (interpolated) pixels or visible gaps between pixels
mikehit e2
5 7.1k 11 United Kingdom
7 Jul 2011 12:37PM

Quote:"this is how big your file should be to produce a half-decent print".


But at what dpi (180 vs 200 vs 300)? The article only addresses that much further down. The information may be there but the flow of information (the way it is presented, if you like) is crucial and this had me trying to untangle it.
It may seem obvious to you but as the article is aimed at people who do not know anything about it, then it should not be making assumptions if you want to get the message across. The part about printing at 180 vs 200 vs 300 dpi is fine - I just did not find the link between ppi and dpi at the start of the article to be as well done as was intended and the part I quoted was just part of that.


Quote:but article is talking about minimum sizes for a half-decent print


surely it was about maximum sizes ....Wink

I am trying to make constructive criticism here as someone who is not hugely technically literate and hates making assumptions when reading articles meant to explain things.
User_Removed 10 3.3k 4 United Kingdom
7 Jul 2011 6:11PM
Mike it was about the minimum size of your digital file or the maximum size of your print. I'll try to simplify it for you to the extreme.

To get top class results you need to print about 300 pixels for every inch of paper. So if you want something 10 inches wide you need a file 3000 pixels wide.

10 x 300 = 3000 (or 3000 divided by 300 = 10)

You shouldn't need a table, the arithmetic really is that simple.
User_Removed 5 4.6k 1 Scotland
7 Jul 2011 7:44PM

Quote:the general worry about unaccredited "experts" talking rubbish on internet sites still applies.

Lol LF it was only a few weeks ago [here] that you told somebody they needed to set their images to 72 ppi before uploading. "72 is the best. Any more just increases file size for no benefit when viewed on a monitor." which is, to use your word, RUBBISH



Chris,

You really are an ignorant sod, aren't you?

I am not trying to be unkind, but you are totally missing the point here (as you seem to do most of the time).

The point is this. On an internet discussion forum, like this one, it is to be hoped that most contributors recognise that a range of opinions will be expressed, some of which will have more knowledge and expertise behind them than others. Sometimes contributions are well-founded, sometimes they are just plain wrong, sometimes they are opinionated, sometimes they are humorous, sometimes they are provocative, etc., etc. That is the nature of internet discussion forums.

I have actually seen some beginners getting very good advice on here and I have also received some very helpful comments when I have been trying to solve a problem or two.

But the huge difference between contributions to a discussion forum and a published article is that, in the latter case, readers will sometimes assume that the writer, merely because he has been published, knows what he is talking about. How often do seekers after knowledge now use Google to find information. If they do that and find a seemingly authoritative published article, they may be misled into thinking that the information is sound. As the author of over a dozen published and highly regarded books, some of which are best-sellers in their field (not photography I hasten to add), I am very aware that sometimes what I have written is afforded a degree of authority that I would never have claimed - but at least it has been peer-reviewed before publication and then subjected to expert criticism after publication.

In this "information age" when so much is published spuriously on the internet, often without even the precaution of peer review, I can't see an easy answer to this - other than to point out whenever we can, where obvious errors are being promulgated. OK, it might not be popular with the authors, but have you a better idea?

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