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Re: [OM] how many megapixels here?

Subject: Re: [OM] how many megapixels here?
From: John Hudson <OM4T@xxxxxxxxxxx>
Date: Wed, 02 Dec 2009 12:22:00 -0400
Pixels per inch "PPI" and Dots per Inch "DPI" are different concepts.

PPI refers to the pixel resolution of an image. DPI refers to the resolution 
of a printer [so says Martin Evening in his Adobe Photoshop for 
Photographers book].

According to the "New Epson Complete Guide to Digital Printing" book it 
states that "Epson prints at three photo settings: 720dpi, 1440 dpi and 2880 
dpi. Some Epson printers let you choose these numbers; others do not. 
Typically, however, the Photo option selects 720 dpi, Best Photo selects 
1440dpi and Photo RPM gives 2880 dpi"

If Epson could satisfy discriminating customers at the "300dpi" level I am 
sure that their printers would be putting out 2880 dpi

Given this information I suspect that printing at much below "300 dpi" is 
going to produce a poor print.

The question is the relationship between pixels and dots, along with LPI 
[lines per inch] when transforming a pixel measured image into a dots 
measured image on paper.

jh




----- Original Message ----- 
From: "Ken Norton" <ken@xxxxxxxxxxx>
To: "Olympus Camera Discussion" <olympus@xxxxxxxxxxxxxxxxx>
Sent: Wednesday, December 02, 2009 11:51 AM
Subject: Re: [OM] how many megapixels here?


> >
>> Is an 11 Mpix sensor big enough with make a 48" wide image with more than
>> enough fine detail to withstand careful up close scrutiny ?
>
>
> If the edge-sharpness is there, the answer is a resounding yes!
>
> All this talk about maintaining 300dpi for printing is a bunch of hogwash.
> The eye is able to discern a line at 300dpi, but is unable to see anything
> else down there.
>
> To prove me wrong, do the following:
>
> Make an image file in your editor of choice and create a pattern of 1 
> pixel
> wide vertical black and white lines. Print this at 300dpi.  Can you see 
> the
> pattern?  Let's go one step further. Add horizontal black lines.  This
> should give you 1 pixel white dots surrounded by 1 pixel of black.  Can 
> you
> see the dots?
>
> Now, start scaling the images up to 200dpi on the printed page.  Then try
> 150dpi.  Even try 75dpi.
>
> At 150dpi the human eye is easily able to discern the lines and dots
> (provided that the scaling engine didn't blur things too much), but just
> barely. If the edges of the lines remain sharp and not blurred, the detail
> is maintained to the maximum of what the human eye is comfortably viewing.
>
> Now comes the fun part.  I hope that the three prints are identical.
> Randomize the prints and grab one and guess which one is at which
> resolution.  Hand the 150dpi print to another anal-retentive photographer
> and ask him/her what resolution it was printed at.
>
> Folks, when tests like these are performed without bias, you'll find more
> times than not that the lower-res image looks exceptionally sharp and 
> highly
> detailed.
>
> AG
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