I’ve had some interesting chats on the set of the last feature film I DP’d. I was talking to the lead actress and she was asking the difference between resolution and sharpness because she believed they are the same thing. Higher resolution images create sharper images because of a higher pixel count. However, if a high resolution image is “soft” or out of focus, you just have a really big unsharp photo. So in short, high resolution doesn’t = sharpness. Even though this is a common misconception, I’d like to explore this and go deeper.
Let’s start with the definition of each:
Resolution – a measure of the sharpness of an image or of the fineness with which a device (such as a video display, printer, or scanner) can produce or record such an image usually expressed as the total number or density of pixels in the image
Sharpness – : clear in outline or detail : DISTINCT. : set forth with clarity and distinctness.
Resolution and visual sharpness are different items because resolution is a one dimensional parameter and sharpness as the eye sees it is two dimensional.
Clarifying the resolution questions:
When someone mentions resolution, are they talking about the sensor size of the camera, the megapixel count of the camera, or the viewing size of a screen/print. or
There is another factor involved in resolution and that’s your lens. I am not just talking about glass quality. I am talking about lens aperture. You could have a Ursa Mini Pro and it could be less sharp than a classic Alexa. Why? Because there are several variables that impact sharpness and have NOTHING to do with resolution. Putting a cheap lens on the Ursa Mini Pro and an expensive lens on the Alexa, it may outperform the UMP. The same is true if you reverse the cameras.
Assume for a moment that all lenses are created equal. That they are perfectly “sharp”. Here’s how aperture comes into play. You should know by now that an aperture of f8 has a smaller opening than f4. Here’s the problem: light “bends”. It bends when it passes through small openings. We call this diffraction. The tighter the opening, the more light diffracts. It is like a hose with running water. If you squeeze the hose, the water will spread (bend). Squeeze it tighter and the water spreads even more.
Aperture affects resolution in ways that most photographers are not even aware of.
Diffraction is a physical property of the lens. When a lens is set to a high f-stop (small aperture), light waves passing through spread out and interfere with one another in a way that limits the amount of detail in the image projected upon a sensor. A particular camera lens may, for example, project a very sharp image on the sensor at f/5.6, a less detailed image on the camera at f/11, and a less detailed image still at f/22. This is purely a function of the lens aperture and has nothing to do with the sensor resolution (megapixel count).
Sharpness can be subjective and the perception of sharpness is influenced by a handful of factors like aperture, depth of field, shutter speed, lens resolution, and camera sensors. It has a lot to do with contrast too, especially along the edges of objects in a frame. For instance, by enhancing the contrast along edges in an image, a lower resolution image can actually appear “sharper” than a higher resolution image.
Why does a cinematographer want the highest resolution or the sharpest image.
- Oversampling, which basically means getting the most information you can out of the camera, so you can then have the most flexibility in the post production process.
- Repositioning and Re-framing.
- Stabilization
Thanks for reading. Hopefully this help straighten out any confusion.
