How many pixels in a megapixel?

Started Apr 2, 2012 | Discussions thread
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Ed Rizk
Senior MemberPosts: 1,398
How many pixels in a megapixel?
Apr 2, 2012

Don't say a million. If you commit the cardinal sin of pixel peeping from time to time, it is clear that the only useful answer is "it depends".

So many megapixel threads have come up recently, and they all lead me back to this question. I'm no real photographer, but I have been at digital photography for a little over two years now. I peep at pixels periodically to see how photos will work for large prints. Pics that look good on the screen, often will not look good in print, so if you don't want to throw away a lot of prints, you must peep.

The capture of the shot, as well as its processing both seem to affect the usable resolution of the final image. Those 18M pixels start dropping off as soon as you put the camera up to your eye. The fall off continues all the way through the process even to the actual printing.

High ISO yields pics with noise which masks detail. Noise reduction software smears more detail away.

There seems to be less detail in red portions of any picture that other colors in the same light.

When I shot film, I was taught to leave room to crop. This one is obvious, but much larger than you would think. Just cropping to an 8X10 ratio knocks out 20% of your pixels. There is usually more cropping than that for me.

Straightening or correcting perspective causes pixels to be lost since pixels can't be stretched or compressed. They are replaced with other square pixels that approximate your corrected image causing a loss of pixels.

Even adjustments in color saturation appear to kill detail.

Finally, when you go to print, unless the resolution of the printer is exactly the same as the resolution of your file, you lose more pixels in the resizing process.

Of course none of this matters if you are displaying the images at a small enough size. Now that I have upgraded (a year ago) to the 18MP 60D, only the worst problems are visible at 8X10. Lots of the problems with my old P&S shots (9MP) were visible at 8X10. At 16X20 or above, all of the above pixel thieves must be minimized to get a good picture. Sure, some shots look good with a little blur for surreal effects, but more detail is usually better than less detail. The theory of looking at prints from the appropriate distance doesn't hold water. People always look closely to see the detail in large prints.

Even photogs with greater skill than me crop an process most shots. So, on average, how many pixels really are in a megapixel at the end of the day?

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Ed Rizk

Canon EOS 60D
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