Saturday, August 18, 2012

Megapixels and cropping

click photo to enlarge
How many megapixels does a photographer need? That question is as difficult and as pointless to answer precisely as, "Which is the best camera?" It all depends on your requirements in terms of image size and the type of photography you undertake.

If you sell photographs to print publications it's quite difficult to argue that you need more than 8 megapixels in a suitable camera with a good lens.. Why 8? Well, a 10 inches by 8inches photograph printed at 300dpi requires 7.2 megapixels. If you bear in mind that some magazines print at 240dpi and that most single page magazine images are less than 10X8, then 8 megapixels is clearly enough. (You'll have worked out that 5 megapixels is more than enough at 240dpi.) If, quite understandably, you want to allow for reasonable cropping then 12 megapixels is absolutely fine. If you aspire to cover the odd two page spread then 16 megapixels will do it comfortably. The number of megapixels that manufacturers offer us continues to increase, but as the above shows, unless you have a particular requirement to print large, then 8, 12 or 16 is plenty. Moreover, as print slowly gives way to screens in their many guises those numbers become significantly more generous and allow much heavier cropping.

If it isn't maximum detail in very large size prints that is used to justify high megapixel counts then it's the ability to crop and stillretain a large file. There are purists who scorn cropping, seeing virtue in composing using the camera's frame and sloppiness in composing after exposure by trimming bits off the four sides of the image. I have no qualms about cropping. I see no intrinsic worth in the offered aspect ratios of 3:2, 4:3, 1:1 or 16:9. I do have preferences, and some suit a particular subject - say portraiture - but generally speaking they all have their uses. But to find compositions in the world that perfectly fit these proportions is not always easy and can be an exercise in futility. So I think that cropping has its place.

Today's photograph is one that is double cropped. If I had a tilt-shift lens it would be only single cropped. The Broadway Theatre on Broadway in Peterborough is quite a large building, probably a former 1930s cinema, with a recent, rather good, big, glazed extension on the main elevation. Even standing on the opposite side of the road with my widest lens at 17mm I couldn't photograph it with the correct verticals that I wanted for an architectural interpretation of the building. So, I placed it in the frame with plenty of space around it and took my shot. Then I corrected the verticals and cropped the surround (smaller photo above). However, that composition wasn't as good - I think - as the further crop (main photo above) that gives greater emphasis to the people that I had deliberately included. My second crop changes the character of the photograph from architectural to a bit more of a "street" or "urban" shot, and makes an image that I like better. It's not the way a purist would shoot, but I see no problem with it. The original shot was 21 megapixels: the second crop took it to 15, and the final crop to 9 megapixels.

photograph and text © Tony Boughen

Photo 1
Camera: Canon
Mode: Aperture Priority
Focal Length: 17mm
F No: f8
Shutter Speed: 1/500 sec
ISO: 100
Exposure Compensation:  -0.67 EV
Image Stabilisation: On