raw dpi? 5d mkiii, quick Q

[nick_kuskin1]

<p>A multiple of stepping technology is exactly what it is I think. RGB LED/white light going thru something that spins, and a very good microscope lens. I think. Thanks. And Thanks! for the bigger description.</p>

[zml]

<blockquote>

<p>DPI is the relationship between pixels and inches, period</p>

</blockquote>

<p>No. That would be PPI (= pixels per inch.) DPI is a printer, or monitor, measure (=dots per inch) and is usually stated as two values: vertical and horizontal spatial "printer resolution", say 2400 x 1200 dots per linear inch. In other words, PPI refers to input and DPI to output. The value embedded in straight out of camera files is really PPI and, with its default setting of 240, it means that from a 2400x1200 pixel file one can print a 10x5 inch image using 240 pixels per linear inch of output. <br>

240 PPI is considered photographic quality (let's not debate this point here...) hence the default value.</p>

[Mark Keefer]

<p>@Jeff Dots Per Kilometer, lol, printing some very large photos. That's a lot of dots.</p>

[Mark Keefer]

<p>Posted before I saw the correction on the next page. :-)</p>

[john tonai]

<blockquote>

<p>@Jeff Dots Per Kilometer, lol, printing some very large photos. That's a lot of dots.</p>

</blockquote>

<p> <br>

Or REALLY BIG dots ;)</p>

[Andrew Garrard]

<p>Michael: If only it were that simple. There are printers (such as the HP that I referred to above) that only accept content up to 2400ppi, but actually control their output at multiples of this to allow dithering at the pixel level. There are printers that control the size of their dots, though this is often a print speed optimization measure. There are some printers that can genuinely print analogue pixels (dye sublimation printers, for example); going with "dots" is confusing even with the average 7+-colour photo printer. On the other hand, "ppi" is pretty confusing even for computer displays (does it refer to sub-pixels, to RGB triples, how about RGBW or RGBY? how about delta-nabla displays? PenTile RGBG? eInk?) and to camera sensors (Bayer? Foveon? Fuji odd layouts? RGBW? what about low-pass filters? what about Hasselblad's sub-pixel sensor/shift? how about scanning backs? film grain? how much can we reconstruct from multiple video frames? how much sensor noise is impacting reconstruction algorithms?)<br />

<br />

Speaking as a computer graphics professional, going back to the days when a lot of monitors really were bi-tone and "dots" made sense for the screen, I suggest letting it lie. We can normally work out what we mean when we say dpi or ppi, in as much as anyone ever needs to know. You're quite right that 240ppi is there because it's as good a default for "probably can't see the dots" as any (though most people actually tend to use 300ppi for that arbitrary figure), and because the figure in the JPEG file is typically utterly irrelevant. If I ever invent a time machine, I'll go back to the meeting where someone decided to encode this figure in the image format and have words with them. :-)<br />

<br />

Nick: Cool. I hope you have fun with it!</p>