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photo:megapixels

megapixels - how many is best for you?

Introduction

  • the initial thought for most people who don't understand photography and its nuances is that more megapixels in a camera is better - but they would be WRONG!
  • for most people somewhere between 16-24 megapixels is probably the sweet spot and having more megapixels will probably NOT get them better image quality but more problems

How many do you actually need?

  • the current 16-24mp sensors give more detail than the traditional 35mm full frame film cameras
  • in general, you cannot tell substantive differences in image quality in prints until you double the resolution, however, this doubling factor probably only works for sensors 30mp or less as sensors greater than this may not result in substantive better images for the reasons outlined below
  • if all you do is post to the internet:
    • Instagram
      • 1080×1080 square (1.2mp) or 1080×1350 (1.5mp)
      • note that when posting to IG, you WILL NEED to crop your images to their ratios as above, so if you have a 3:2 sensor such as is found in all APS-C and full frame cameras, you need to do a LOT of cropping - the issue is MUCH LESS in Micro Four Thirds system cameras as they have a 4:3 aspect ratio which is much closer to the IG standard
    • most other photo websites
      • protect your images by keeping your net images restricted to 1200px on the long side = 2.2mp
  • printing to 30“ x 40”
    • very good results are possible with well taken images at 12mp
    • those who want better close up viewing resolution 20-24mp will be better (in some situations up to 45mp may give better prints in some circumstances when printed to 50“ size and viewed up close)
    • remember the larger the print, the further away your viewer should be so you really should not need more than the above, this is why Apple promote their iPhone on road side billboards showing images taken with there 8mp iPhones blown up still look great

The problems with more megapixels

  • large file sizes which means:
    • slower shooting - these cameras generally have slower burst rates and take longer to clear the buffer so you can continue shooting
    • the need for larger memory cards and hard disk drive storage
    • slower backup times (especially to the internet)
    • much slower post-processing which can become extremely frustrating
  • more image noise and poorer image quality at higher ISO levels
  • issues with producing video outputs which need far less megapixels
  • cameras are usually sold at higher premium prices
  • YOUR IMAGE QUALITY MAY WELL BE WORSE or ONLY MARGINALLY BETTER (see below)

The supposed benefits of more megapixels

  • ability to crop more
    • this may hold true for some subjects and situations but see limitations below which means you probably will not get that great a benefit from the extra megapixels in reality
    • there is a reason the pros buy those big, heavy, ultra-expensive super telephoto lenses instead of just cropping
    • but what about cropped sensor cameras you say?
      • the difference here is that in general, their lenses are optimised for the higher pixel density count and to have this level of optical quality across the whole image in a full frame lens means very expensive and heavy lenses
  • smaller image noise
    • well this probably does hold true, while you get more image noise with higher pixel density sensors, the higher the megapixel count means that each individual component of the noise is smaller and thus more easily managed
  • larger print sizes are possible
    • under studio situations with optimum techniques and equipment and with no moire issues this may hold true
    • for most other circumstances the validity is questionable (see below)
  • commercial agencies or clients may prefer larger resolutions
    • this may be true and may be important for some pro photographers

Why your 80mp sensor camera may not give significantly more than 24mp image quality

  • to achieve greater image detail with the extra pixels you need EVERY one of the following to be present:
    • high optical lens quality
      • a lens initially released before 2010 is unlikely to have the optical quality to achieve better than 24mp and many of the “pro” 35mm film camera lenses probably struggle with 16-24mp
      • even with a superb new design lens, it must be used at its peak performance to avoid diffraction aberrations at smaller apertures which will quickly make all those extra pixels useless
    • super accurate focus
      • you will only see the benefits of more pixels if you are magnifying the image and this means your acceptable zone of sharpness becomes razor thin - any mis-focus becomes very evident and even having more depth of field (DOF) will not address this issue well
    • subject MUST have detail as well as be in the focus plane
      • in fact, the benefit of those extra pixels is ONLY going to be realised in those areas of the image which have tiny details and are in the focus plane, all the out of focus areas or those areas with no details (eg. blue sky), will have NO benefit from more pixels, and one could have just have easy used editing software to interpolate those areas to make the final image larger
    • a subject that is NOT moving
      • sure you can use really fast shutter speeds to “freeze” the subject, but most sports photographers would probably only get around 10mp of detail due to the issues of camera movement and subject movement
    • camera is not moving
      • camera sensor based image stabiliser becomes very important, and even resorting to tripods may be required, but even these may result in camera movement if there is wind or the surface itself is moving
      • for super telephoto lenses these tend to keep shaking for some seconds after the shutter button is depressed and any such shake may rapidly degrade the image wasting all those extra pixels
      • many cameras also have shake caused by the mirror or the sensor shutter mechanism which may require mirror lock up and 1st shutter set to electronic rather than manual
    • subject MUST be relatively close
      • more than 10m or so of air creates aberrations which will degrade image resolution (similar to looking down an airport runway on a hot day)
      • this is one of the reasons why:
        • the argument that lots of megapixels allows one to crop more has limitations - the air is going to make things more blurry anyway if the subject is a long way from the camera
        • the argument that you need lots of pixels for a large landscape print may not be valid if that image are obtained in a single shot - distant features in a landscape will be blurred due to the amount of air between the camera and the subject, especially if one shoots into the light

alternate means of getting more pixels

  • panoramic stitching
  • sensor shift multi-image High Resolution mode (eg. Olympus Hi Resolution mode) - this has the advantage of reducing moire effects but is limited to static subjects
  • medium format sensor with more megapixels is not as demanding on the optics as the pixel density can be retained at a lower level and allowing pixel size to be large giving better image quality
photo/megapixels.txt · Last modified: 2019/01/21 11:48 by gary1