How Many Megapixels (MP) Are Required for X Print?
by daniel on Nov.25, 2009, under Photography
Many of you are probably thinking/asking how many megapixels are required for a 4×6 print? or a 8×10? or a 24×36?
Here is a small table of the minimum sizes (at 300dpi) high quality:
| Printed Size | Min. Resolution | Megapixels |
|---|---|---|
| 4×6 | 1200x1800px | 2.2 MP |
| 5×7 | 1500x2100px | 3.2 MP |
| 8×10 | 2400x3000px | 7.2 MP |
| 8.5×11 | 2550x3300px | 8.4 MP |
| 13×19 | 3900x5700px | 22.2 MP |
| 20×30 | 6000x9000px | 54.0 MP |
| 24×36 | 7200x10800px | 77.8 MP |
Here is a small table of the minimum sizes (at 150dpi) bare minimum:
| Printed Size | Min. Resolution | Megapixels |
|---|---|---|
| 4×6 | 600x900px | 0.54 MP |
| 5×7 | 750x1050px | 0.8 MP |
| 8×10 | 1200x1500px | 1.8 MP |
| 8.5×11 | 1275x1650px | 2.1 MP |
| 13×19 | 1950x2850px | 5.6 MP |
| 20×30 | 3000x4500px | 13.5 MP |
| 24×36 | 3600x5400px | 19.4 MP |
As you can see, actual pixel count is fairly demanding for a “high quality” print. High quality meaning what is actually observed by the camera and not made up by some computer program. Typically computers are used with a algorithm called a Bayer Interpolation that will blend and “guess” the colors to make up missing information between colors and pixels when someone tries to enlarge them, so it is possible to get an OK looking 8×10 from a 5 MP camera, or an OK looking 24×36 from a 22MP camera. So keep in mind that if you are producing any of these sizes with less than the Megapixels listed your print is more a test of the quality of your computer software than it is your camera!
Also keep in mind that imaging sensors will see only one color and one intensity per pixel. So 1 px will see red at lets say a value of 210 (1 to 255 intensity, 16 Bit color). In order to record the real color emitted in real life you need at least 3 of these. Yes, just like your TV or anything else the camera will blend the 3 colors to create the real “observed” color. What is the caveat for this? Digital cameras (non-Foveon) only really “see” 1/3 of the claimed Megapixel value that they advertise (because they are using 3 pixels to record each “real” color) so that fancy 10 MP camera you own in reality only can record 3.3 MP worth of actual real life image, just enough for a high quality 5×7, the rest is blended and made up by computer software. This makes a strong case for the reason why REAL professional photographers still use film for all of their important work. This is because film CAN record a real color at each “pixel” which is still higher than digital (roughly 88 real megapixels for a 35mm piece of film).
December 3rd, 2009 on 12:22 am
Hmmm, where to begin…?
— Computers don’t use Bayer interpolation; camera imaging sensors do. Bayer interpolation is how the sensor gets three color values (R, G and B) for each pixel position, even though each sensor pixel is covered by only one color in the filter mosaic; the interpolation derives the other two colors.
That means it’s only the color value that’s interpolated, not the brightness value… so your statement farther down that “digital cameras… only really ‘see’ 1/3 of the claimed megapixel value” is also off-base, because it’s only the color data that’s interpolated; the luminance data, which accounts for most of what the eye registers as detail, is per-pixel accurate.
— Your “How many megapixels are required for an N size print” chart is unrealistically demanding; in real life, not nearly as many pixels are needed as the chart shows. That’s because very few output devices actually resolve 300 machine pixels per inch.
Even those that run the print engine at 300 ppi don’t actually resolve that much, because the dye spreads into the emulsion; in practice, a viewer won’t be able to see any difference between a 300ppi print and a 240ppi print, and most people find a 180 ppi print just as acceptable.) For a chart based on real-world output devices, see here:
http://ranger9.net/?p=46
The practical criteria actually get less demanding as prints get larger, because people seldom examine a 24×36 print at nose-touching range. So a letter-size print, which is about the largest size you can examine conveniently at reading distance, typically is the worst-case scenario. On the other hand, you can easily blow up a 6-megapixel image to billboard size, since nobody sees a billboard from less than hundreds of feet away!
— “REAL professional photographers still use film for all of their important work”… really? My employer buys a couple of million dollars’ worth of high-end studio photography per year, and ALL of it is shot as digital — guess either those guys aren’t “REAL professionals” or they don’t regard my employer’s work as “important,” huh?
C’mon, be serious — we all love the aesthetics of film and it’s still a great medium of artistic expression, but anti-digital hype is SO 20th century. If your final deliverable is a digital image — and for commercial use, that’s almost always the case — you get a cleaner file if you start with a digital original.
Besides, there’s no way you’re ever gonna scan a full “88 megapixels” worth of actual data out of a piece of 35mm film… once you crank your scanner much past 4000 ppi, all you’re doing is imaging more grain and dust! (On the other hand, if you’re talking about an 8×10 transparency on a drum scanner, THEN maybe you can convince me! A lot of high-end catalog work still gets shot on sheet film.)
Oh, well, snark mode off — thanks for a fun challenge, at least! And I love what you’re doing with your RX8!
December 3rd, 2009 on 1:17 am
Josh! How ya been?
December 3rd, 2009 on 1:19 am
PS – You know me, I AM unrealistically demanding
Lol
March 1st, 2010 on 10:14 am
hi, can u say in 1 frame how many pixel will be there…