How many pixels are enough?

French Patisserie, 4Mpixel - 69AC0777/2002

As I reshape my photography direction I have been prompted to think about what I need from my camera. The launch of the 40-50Mpixel Canon and Sony camera bodies has generated a new question—do I need that many pixels?

I quickly came to the conclusion that I do not. As I consider how my photographs are used by me, and by clients, it is clear that most of the time I have very modest needs. However as I am moving into art photography there is a part of my future work where the demands are higher, but it seems they still not need the 40-50Mpixel of the new generation of full frame cameras.

Uses and image file size requirements

Most of my photographs are used for editorial purposes in magazines and on web sites. Even at 300dpi a double page spread only needs 5,000 pixels on the long side, in reality 16Mpixel would be enough. For many publications 200dpi would do so 3,500pixels would suffice. Often smaller still would be sufficient, I have recently sold a three page article to a magazine and the largest picture is a just under half a page. I knew that they would not be using my pictures as a double page spread or a cover so I sent 6Mpixel files (3,000pixel on the long side) to make transmission quicker and easier. [ask DK what dpi F2 magazine uses]

Detail: French Patisserie, 4Mpixel - 69AC0777/2002I am aiming to do much more art photography where I will need to create large display prints. I expect most will be around 18x12in (45x30cm) or about the size of a double page magazine spread. At first that suggests that 5,400 x 3,600pixels would be needed, or nearly 20Mpixel. Actually that is not really necessary, because as the print size increases so does the viewing distance. A book or magazine is viewed at arm's length, say 18in (45cm) but a typical wall print is normally going to be viewed at twice that distance, at least. Doubling the distance effectively halves the effective size of the dots that we can actually see—so, my 18x12in prints could be printed at 150dpi and still look crisp at normal viewing distance. As art is about quality I will aim to print much finer but 16Mpixels would still give nearly 300dpi at that print size. Obviously viewers of art works do sometimes get in close to look at the detail but a 16Mpixel 18x12in print will have as much fine detail as a similar sized print from film, especially 35mm. At that size film grain will be visible close-up even without a magnifier; no one considers that unacceptable. Indeed, I have an 18x12in  picture on my wall (heading picture of patisserie, detail right) that was printed from a 4Mpixel file (original Canon 1D) and the detail is very acceptable, even viewed closely.

Optical limits of the human eye

This experience is confirmed by physical limits to the capability of the human eye. The visual acuity of the human eye due to the spacing of cones (light detectors) in the retina give a theoretical limit of resolvable detail around 250dpi at a minimum comfortable viewing distance (for a young adult) of 25cm. For an older person that viewing distance will be greater and the resolvable detail correspondigly lower. In reality the visible fine detail is actually about half that ideal as the eye is diffraction limited, the size of the pupil of the eye 'smears' the detail of a point over adjacent cones. That explains why my 4Mpixel patisserie print looks acceptable, it is printed at 125dpi, the diffraction limit of the eye at 25cm. In practice even that is finer detail than most people's eyes will be able to resolve and in any case that print will usually be viewed at more than twice the 25cm minimum distance used to calculate that resolvable limit. So very large prints should be acceptable even if printed at 100dpi or less. As a result of the viewing distance billboards can be printed at 10-20dpi.

To confirm these principlse I am going to be running a test by making a much larger prints from 16Mpixel files from my Fuji X-T1. Extending the argument above I am going to make a print a metre (39in) or wider. That will effectively be printed at around 100dpi, less than my 4Mpixel patisserie print, but as it will normally be viewed at 2-3m it should be as acceptable as a  hand held 12x8in print from the same size file. From past experience, and comments from other photographers,  I fully expect it to be satisfactory for most purposes.

Art and quality demands

The art market is a wide one and increasingly collectible photographic art is not just about large gallery sized display prints. Photographers are turning to books, small prints, even electronic forms of presentation to meet changing market expectations. In reality it is often easier to sit in a comfortable chair with a smaller print or a book (or even a tablet computer) that can be held in the hand. Such a situation provides the ambience, time and comfort to really consider the work, far more than may be possible stood in front of a print on the wall. Indeed, it can be argued that not all images lend themselves to big display prints. Each subject and the artist's interpretation has an optimum size for its presentation; in many cases that may be quite small. For most of us the great images with which we are familiar, and which have moved us, we know from books and magazines rather than gallery displays. Smaller is sometimes better. Such hand held prints are usually smaller than even a magazine double page spread, the familiar 10x8in justifies its classic status. So again 16Mpixel is a big enough file even for images subject to close scrutiny.

Enough is enough

All things considered, it seems that around 16Mpixels are enough to produce high quality for most purposes. So my decision to go with the 16mpixel Fuji X series makes sense as it will produce the output quality I need for my business and artistic purposes. However, I am looking forward to the next generation Fuji X cameras which will give 24Mpixel files (the X-Pro2 has just been launched, I await the X-T2). It is not so much for the higher resolution but to give more flexibility when I need to crop or straighten up an image.

However, similar thinking has an impact on the specificication of the monitors for our editing workstations. That is the subject of My view on pixels has changed, my next post.

It seems I have the equipment that is more than adequate to support my business objectives, to provide high quality collectible art. I now need to refine my technique and vision, build an audience and a client base for my work. But they are different stories, for another time.

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