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Is it the sensor to blame? Because film-based pictures do not need sharpening.

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    \$\begingroup\$ Who says that? Sounds like B.S. to me, or a poor demosaic algorithm. \$\endgroup\$
    – Itai
    Commented Jan 8, 2014 at 4:39
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    \$\begingroup\$ @BBking The use of unsharp masking to make an image sharper in the darkroom has been used since at least the 1930s. en.wikipedia.org/wiki/Unsharp_mask \$\endgroup\$
    – Michael C
    Commented Jan 8, 2014 at 7:14
  • \$\begingroup\$ More exactly, I was browsing at the library and found a book that said so. I think the aothor was *. Fraser? \$\endgroup\$
    – angel rojas
    Commented Jan 9, 2014 at 5:14

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There's two mistaken statements in your simple question: first, that sharpening is always needed for digital photographs, and second, that it's not needed in film.

Let's start with the second. Film actually isn't fundamentally different here. Scanned photos often benefit from digital sharpening to match the output medium. But not even digital: the common "unsharp mask" digital sharpening technique is called that because it is based on an analog technique used with film.

It is true, though, that there are some things about digital sensors that mean that sharpening is a normal part of the workflow. One of these is that most digital cameras include an antialiasing filter to help reduce moire. That works by introducing blur, so sharpening counteracts that. Also, sharpening needs to be part of interpolation when using a Bayer-pattern sensor. Digital leaves you the flexibility of leaving that sharpening for the end of your workflow rather than locking it in. Depending on your sensibilities, though, you might decide that sharpening isn't needed at all.

But also, digital photography has ushered in trends that aren't related to needing sharpness in an absolute sense but are definitely related to an obsession with it. People tend to view images on computer screens, in high resolution, and when critiquing them, zoom in to 1:1 pixel view. This is like scanning over every photo with an extreme magnifying glass; in the film days, some people did this, but most people recognized that you could appreciate a photo without doing it. Now, sometimes, people get an obsession with a certain sort of technical perfection in their photographs (often to the detriment of artistic qualities, or even more complicated technical qualities).

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  • \$\begingroup\$ I think its commonly said that you need to sharpen for your target viewing size, which may simply get understood as a general need to sharpen. This answer kind of says how to choose an appropriate sharpening radius: photo.stackexchange.com/a/9447/889 \$\endgroup\$
    – drfrogsplat
    Commented Jan 8, 2014 at 6:45
  • \$\begingroup\$ I don't get that part about film. I don't know a way to "sharpen" film photographs if not by manual retouching to enhance edges. When you use a scanner to digitize a film photograph it no longer is what was meant in the question, the way I read it. \$\endgroup\$
    – Esa Paulasto
    Commented Jan 8, 2014 at 9:59
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    \$\begingroup\$ en.wikipedia.org/wiki/Unsharp_masking makes a good explanation of how unsharp masking works with film photographs. \$\endgroup\$
    – Cornelius
    Commented Jan 8, 2014 at 14:36
  • \$\begingroup\$ @Cornelius - Thank you for the link. A great explanation there. \$\endgroup\$
    – Esa Paulasto
    Commented Jan 8, 2014 at 22:41

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