Doing the Math

[Sanford]

<p>At 300 dpi, a photo taken with an XE1 opened in PS measures 10.88"x16.32" for a total of 177.58 square inches. A photo taken with a Lumix GX1 measures 11.5"x15.3" at 300 dpi for total of 176 square inches. Virtually the same! </p>

[Charles_Webster]

<p>DPI specs of files are meaningless. Only when printing does DPI have any meaning whatsoever.<br>

What are the pixel dimensions of each camera? That's the meaningful measurement.<br>

<Chas><br /><br /></p>

[bebu_lamar]

<p>But it does mean that both cameras have about 16MP. You asked to do the math so I did.<br>

The XE1 has 15,980,544 pixels and the GX1 has 15,835,500 pixels.</p>

[Sanford]

<p>Should have said ppi, not dpi. Both cameras are 16mp.</p>

[andylynn]

A shot from a Nikon D4 would also be around the same size at the same PPI, as would a Galaxy S5 phone. It just goes to show that

megapixels aren't the only measure of an image.

[bobatkins]

<p>Figures often beguile me," wrote Mark Twain, "particularly when I have the arranging of them myself; in which case the remark attributed to Disraeli would often apply with justice and force: 'There are three kinds of lies: lies, damned lies, and statistics.'"</p>

[Karim Ghantous]

<p>My take-away message here is that statistics is an unfairly treated discipline.</p>

[bebu_lamar]

<p>So to the OP what's your point on this?</p>

[Sanford]

<p>The point is that M4/3 and APSC produce essentially the same square inches of photograph.</p>

[bebu_lamar]

<p>That is no point. Any 16MP camera of any size sensor would produce the same that including the older medium format cameras with low pixel count and the current Nikon D4s and Df. </p>

[Matt Laur]

<blockquote>

<p>The point is that M4/3 and APSC produce essentially the same square inches of photograph.</p>

</blockquote>

<p>Which would be relevant if the only thing that mattered were the presence of the the number of pixels in the output. We can look at 500 words typed by a child on an iPhone, and 500 words written by Shakespeare, and say, "Look, it's 500 words either way, so they occupy the same amount of paper when printed." Which doesn't shed much light on things, either.<br /><br />Smaller format cameras have immediately obvious shortcomings for certain kinds of image-making. They have some advantages in others. A lot of people never notice, one way or the other. I know I do. I regularly use stills from a GoPro (at 12MP), or might take a roughly 12MP chunk out of the middle of a frame recorded by a DX or FX Nikon body or an APS-C Sony mirrorless or video body. Talking pixel count is like talking word count.</p>

[frode]

<p>PPI (pixels pr inch) is a scaling factor, nothing more, nothing less (just as DPI is, but then you are talking about dots pr inch for a printer). It says how large you intend to print the image.</p>

<p>Say you have a 3000 pixel wide digital picture from your camera, if you print this picture with 300 pixels pr inch, your image will print 10 inches wide (you need 10 inches to print all the 3000 pixels in the image). If you instead print it at 3000 pixels pr inch, your image will print 1 inch wide (you need only one inch to print all 3000 pixels).</p>

<p>The "math":<br>

(printed image width in inches) = (digital image width in pixels) / PPI</p>

<p>Same for image height:<br>

(printed image height in inches) = (digital image height in pixels) / PPI</p>

<p>Note: The PPI could also be used (and is sometimes used) for scaling the image when displaying it on a computer screen. This is however not normal. I guess this is because one usually wants to display the image with the computer screen's native resolution (the screen's PPI) to avoid artifacts like moire and blurring (the later possible corrected for with an automatic sharpening that usually is not very predictable). One just re-samples the image to a reasonable pixel width and height that one guesses will show the image in a usable size on most computer screens (like for example 400x600, 600x900 or somewhere thereabout) and hope for the best.</p>

<p>Hope this was of some help. If not, print it out, crumple it up and throw it in the bin.</p>

<p>HNY & regars,<br>

Frode Langset</p>

<p>(and excuse my English, its not my native language)</p>

[Ed_Ingold]

<p>An unsophisticated viewer like Microsoft Internet Explorer or Safari will display an image on a pixel=pixel basis. The actual size will depend on the size of the image (in pixels) and the resolution of the screen.</p>

<p>An advanced viewer like Photoshop has several options for display - the scaled size, 1:1 (pixel = pixel) or 100% (fills the available screen). The image display can be scaled any place in between (or even beyond). You must enter the actual screen resolution to display the scaled size. It defaults to 96 dpi, which is often close enough.</p>

[q.g._de_bakker]

The important bit however is the one brought forward by BeBu and Andy: so what that they bpoth produce X MP? It's the quality of what is filling up this in itself empty metric that counts. So even though 16 MP = 16 MP, there is no comparison.

[rashedahmed]

<p>Your 8 MP mobile phone camera image will give the same or nearly same as your 8 MP DSLR image size. But the quality of images will not be the same because of sensor size and fine optics.</p>

[ljwest]

<blockquote>

<p>The point is that M4/3 and APSC produce essentially the same square inches of photograph.</p>

</blockquote>

<p>If, and <strong>ONLY</strong> if the megapixels and the DPI/PPI displayed or printed at are the same (or very close). The same does not hold true if the APS-C sensor is 18MP, and your M4/3 is still only 16 MP. Or v-v.</p>

<p>Bombshell: my Canon 7D (APS-C) takes pictures the exact same size as a Canon 1D X (Full Frame)! They're both 18 MP sensors, so when displayed or printed at the same DPI/PPI, the area (and in this case, the dimensions) are exactly the same. </p>

[Sanford]

<p>Now that makes sense! How do the printed photos compare?</p>

[q.g._de_bakker]

Charles', BeBu's, Andy's, Bob's, Karim's, Matt's etc. responses all made perfect sense, Sanford.<br>It's not how many, but how good or bad those many are that matters.