Troubleshooting Photos –
About the Printable Size of Photos
How big can you print your photos? Or, put another way, how many megapixels does your camera need for you to print pictures at the sizes you want? Here's the 'simple' answer – a table of the standard sizes of print that can be made from a camera of X megapixels, where X is any number of megapixels from 2 to 10. This table is based on three assumptions:
- you will print the photo as it comes from the camera, full-frame, without cropping or enlarging;
- you have learned the rule of thumb that says you should print at 300 pixels per inch – but you've also learned that there's considerable room for experimentation;
- that in case of need, you will ignore the 300 pixels per inch (ppi) rule and print, when you have to, at much lower resolutions – sometimes much, much lower. We'll get to skirting the 300 pixels per inch rule after the table.
You probably will not find a picture size that's identical to your camera's maximum size in the table. Every camera maker uses slightly different photo dimensions; many makers have several standard sizes. Rather than pick one maker and reproduce his sizes, this table uses rounded-off sizes. You may not find exactly the image size produced by your camera, but you should find something close.
Table of megapixels to printable sizes
| Megapixels | Approx. pixel dimensions | Max. print @ 300 ppi | Max. print @ 200 ppi |
| 2 | 1600 × 1200 | 5.3 × 4.0 in. | 8.0 × 6 in. |
| 3 | 2050 × 1540 | 6.8 × 5.1 in. | 10.2 × 7.7 in. |
| 4 | 2270 × 1700 | 7.6 × 5.7 in. | 11.4 × 8.5 in. |
| 5 | 2590 × 1940 | 8.6 × 6.5 in. | 13.0 × 9.7 in. |
| 6 | 2820 × 2110 | 9.4 × 7.0 in. | 14.1 × 10.6 in. |
| 7 | 3070 × 2300 | 10.2 × 7.7 in. | 15.4 × 11.5 in. |
| 8 | 3260 × 2450 | 10.9 × 8.2 in. | 16.3 × 12.2 in. |
| 10 | 3470 × 2740 | 11.6 × 9.1 in. | 17.3 × 13.7 in. |
300 ppi vs 200 ppi – what's the visible difference?
Virtually every source advises you to print photos at 300 ppi, and when you can do so, that's the 'safe' thing to do. The way newer printers translate pixels into print is now so sophisticated, though, that you can go much lower than that. So, don't panic if your preferred print size will come in at a lower value. The differences between two prints of this brooch, rendered at 200 ppi and 300 ppi from the same file, are so slight that you have to look carefully at the prints to see the differences, which are all but invisible in these scans. This is surprising because the original has considerable fine detail and many sharply defined edges, both of which normally reward greater print resolution.
Where the differences are visible – Differences show up along straight lines, and the slightly greater 'granularity' of the 200 ppi print starts to show up in this 3X- enlargement of the scanned prints. You need good eyes to see this even in the original prints.
Bending the rules
Many people are happy with 4-by-6 inch (or 10-by-15 cm) prints, so if you always print the full frame (the whole photo as it comes from the camera), a 3- or 4-megapixel camera may be all that you need. The ease of editing photos on a computer, though, is a powerful inducement to start tinkering, even if you've never before thought of doing anything to a photo. Once you start chopping and changing, you may find that what remains in your cropped photo may not have enough pixels to print at rule-of-thumb sizes. Or – by virtue of the freedom to experiment, you're taking photos you want to see at sizes larger than the old 4-by-6 inch prints.
Depending on what you like to photograph, this issue might arise once in a blue moon or frequently. If it's a rare occurrence, then a camera with a higher megapixel count is nice-to-have rather than essential. If your photos often are starved for pixels, or you want the greater detail that is sometimes available with a higher pixel count, then 6- or 10-megapixels is going to look more worthwhile (or you should think about getting closer to your subjects).
The generally accepted rule of thumb is that a photo printed at 300 pixels per inch will show all the detail that is contained in the original photo. Then, it's a sliding scale down to around 200 pixels per inch (some authorities say 220, so many editing applications warn you in the print dialog if you're about to print a photo below 220 pixels per inch).
Although most subjects can be printed at resolutions less than the optimum 300 pixels per inch, there comes a point where the photo starts to look "soft" (that is, there isn't much detail in places where you know it should be) and ultimately, blurred. Softness and blur kill the illusion or reality. This sequence of prints shows the effects of low resolution, and the improvements yielded by higher resolutions. Accordingly, it's a good idea to set your camera to the highest pixel dimensions and highest quality settings; you can always knock back detail but it's hard to fake it if detail isn't there to begin with.
Finally, no matter what the scene, differences in level of detail won't matter if viewers are never going to get close to a print; look at this sequence of prints from double, then treble your normal viewing distance. The differences quickly cease to matter (many advertising placards are rendered at around 72 very large pixels per inch; any finer resolution would be wasted at normal viewing distances).
Also, acceptable detail depends on your audience. If you take photos at an auto race, most people will see a colorful scene of thrills and speed. A serious auto-racing fan, though, will want detail and more detail, so you'd better be sure those details are visible).
If the file size is so low relative to the intended print size that the resolution will be lower than 240 to 200 ppi, it may be worth your while to re-sample the photo to a file size that will yield around 300 ppi at the size of the finished print. This will almost always yield visibly better print quality.
In a photo like this, a highly detailed print is nice-to-have rather than essential, because the point of the picture is not the fine fissuring of the huge cliff, but its scale and outrageously vivid – and unretouched – color. Note, though, that detail and the textures that it provides add to the overall credibility of the photo; if all detail were lacking, the photo would lose much of its impact. On the other hand, see also this landscape; distance and scale have turned the scene into an array of brushstrokes. Whether the scene is improved by the textures within each body of color is a matter of artistic preference rather than an absolute.
Taken with a cellphone camera, this photo of a girl was only 450 by 200 pixels – a low-resolution JPEG of only 16 Kb. Using the 300 ppi standard, its maximum printable size is a postage-stamp-like 1.5 by 0.6 of an inch (4 cm x 1.5 cm). Because of its dreamy, gauzy quality, most viewers won't expect it to have much detail or definition, so it was possible to make her an 8 inch (20 cm) high print that she thought was just fine.
