A&P The zone system, bit depth, M and AV mode, etc...

Discussion in 'Lifestyle' started by nainline6ftw, Jan 20, 2010.

  1. nainline6ftw

    nainline6ftw Winter is coming

    Joined:
    Oct 6, 2009
    Messages:
    12,298
    Likes Received:
    0
    I mentioned in another thread that I could post about this, and a few people wanted me to.

    [​IMG]

    The zone system, generally credited to Ansel Adams, is a technique used to increase the contrast of a photograph.

    There are 11 zones, each representing a light/dark value. See picture above, it's self explanatory.

    The important thing about the zone system is that zone 5 is middle (or 18%) gray. 18% gray is what a light meter says is "the correct exposure". Which leads me to metering modes...

    Each metering mode is different. The spot meter only meters the light directly in the center dot of the viewfinder. The rest of them take into account the light for the rest of the scene (and makes an average estimate of what most of the scene should be).

    For example, if you metered a black backpack and took the picture based on what the light meter said is the correct exposure, then took a picture of a white sheet of paper the same way, the exposure would make each of them the same shade of grey. When using color/digital cameras, this is harder to see since different color temperatures can cause the illusion of brightness. Nonetheless the important thing to keep in mind is that the meter is always telling you "this is middle grey (or zone)".

    But back to the zone scale. Look at it again. Each zone represents +1 or -1 stops from the middle exposure. Full stop, full ISO, halved or doubled shutter speed, or however you want to look at it.

    So to make a zone 5 exposure into a zone 4, you would underexpose it by one stop.

    Buy why does this matter if the camera can average the exposure of the scene on its own?

    Again, the point of the zone system is to increase the contrast of the photo. What Ansel Adams realized was that when you develop film, the highlights develop faster than the shadows.

    So in other words if you took a picture of say a rock with the sky behind it, you would want to under expose the rocks, that way the blacks/darks in the shadows would would fully develop (turn all the way dark in the solution) by the time the sky was developed. Since the highlights develop faster, exposing dark rocks at middle gray levels would result in either underexposed shadows/rocks or blown out skies.

    How do you know how much to under expose the picture?

    The zone scale corresponds to a stop and a shade. So if you know the camera's spot meter will give you the zone 5 exposure of whatever it is currently pointed at, you need to decide what zone it actually should be.

    In the case of film, you need to find out what the darkest thing that needs to have texture is and expose for that. This describes zone 3 BTW. So you look around and say "these dark shrubs are zone 3", meter it, then underexpose the photo by two stops.

    You run a very low risk of blownout highlights when you do this, so zone 3 is the only thing you need to worry about exposing. It's fine to underexpose the highlights on film because you can just develop the film longer and they will expose WELL BEFORE the shadows will keep exposing.

    So you need to make sure you have all of the details in the shadows exposed right, and compensate the film development time from there. This method will give you negatives with more contrast than is possible using ANY other method.

    OK this is interesting I guess but WTF does it have to do with digital cameras? We have photoshop and obviously don't use film.

    The zone system, surprisingly, applies to digital cameras as well but for COMPLETELY DIFFERENT reasons.

    They also meter 18% gray like film cameras do. So that and the chart is the same.

    The difference, of course, is that digital cameras record images with a sensor. Believe it or not, the sensor is not perfect and there are ways to use it more effectively than others.

    There are two main things you need to remember about digital photographs.

    1.) YOU NEED TO SHOOT IN RAW. Most of the time anyway, if you want a higher quality image. A RAW file has significantly more bit depth than a jpeg file. This means there are more colors and shades, more closely spaced.

    2.) POSTERIZATION / DIGITAL NOISE. Have you seen a histogram before?

    [​IMG]

    Yes you idiot why are you posting a huge histogram picture you stole from googe images?

    The bit depth of a photo is not constant over the entire histogram. Photos have the least bit depth in the shadows.

    Who gives a shit about bit depth when you're posting stuff on the internet and printing 4x6's?

    The problem becomes apparent when you are dealing with an underexposed digital photograph. Trying to bring back the detail on the tires inside your underexposed fender wells? Never gonna happen, you might as well give up and take the picture again.

    The low bit depth in the shadows mean that you are at a high risk of losing shadow detail. If you attempt to increase the detail through Photoshop and increasing brightness/contrast, etc... you will soon find that there are not enough shades of black...

    This results in GAPS in your shit

    [​IMG]

    And shadows that look like this

    [​IMG]

    Oh shit

    Yep that's right, I'm sure you've seen these before. The solution is to OVER EXPOSE the photo.

    Over-exposing a digital photo will bring the shadows towards the middle of the histogram, which has a significantly higher bit depth, and therefore even fairly severe over-exposure can be easily corrected back down to black BUT WITH MUCH GREATER DETAIL than if you exposed the blacks as blacks to begin with.

    This of course means that since you're over-exposing the photo, blowing out the highights is the biggest risk. This means you should expose the picture for the brightest thing that needs to have full detail (zone 7) and don't worry about the rest since anything darker than that can be adjusted to black with not just NO DECREASE in image quality, but an INCREASE in image quality by doing this ass backwards method.

    Anyway, a good example of zone 7 would be a silver car on a cloudy day. Expose the frame for zone 7, so meter the car and do +2 stops. Then the highlights will be properly exposed, and you can photoshop the darks into being as dark or contrasty as you want. You can also expose for zone 6 which is just +1 stop and sometimes safer :o

    A good method of doing this (has to be in raw because raw has high enough bit depth to accomplish this process) is to use the cameraRAW editor or whatever you have and just drag the slider on the black level, increase the contrast, then fine tune the curves. This will bring your weird looking over exposed pic back to normal. Here is an example that I've done:

    Original photo, exposed to about zone 6

    [​IMG]

    Contrast increased in photoshop

    [​IMG]




    As you may notice when you are using your camera in AV mode, the camera adjusts the shutter speed CONTINUOUSLY. If you want to use the zone system you need to remember to meter, then adjust the exposure bias, when focus and compose the shot, then take the picture.

    If you use M mode, you can adjust the exposure for the highlight by pointing the center AF point at whatever you want, finding the proper exposure, then increasing it by one or two zones, without the camera messing with your shit while you're trying to figure all of this out.

    AV mode is obviously better, and more effectively used with a weighted or parietal metering system, for action photography where you have very little time to do anything before you snap the shutter.

    :wavey:

    BTW I haven't re-read this after I typed it so I'm sure there are errors since I'm very :420:

    NOTE: It says zone 8 is the lightest thing with detail but exposing for +3 stops is usually risky and I wouldn't advise it for your first attempt at the zone system
     
    Last edited: Jan 20, 2010
  2. jared_IRL

    jared_IRL OT Supporter

    Joined:
    Feb 12, 2006
    Messages:
    17,737
    Likes Received:
    55
    awesome thread. Gonna read it in depth later, but i've been trying to explain 'shooting to the right' and bit depth here for a while...

    This makes it crystal clear.

    thanks! :h5:
     
  3. nainline6ftw

    nainline6ftw Winter is coming

    Joined:
    Oct 6, 2009
    Messages:
    12,298
    Likes Received:
    0
    Thanks. Hopefully someone will learn something from all of this lol.
     
  4. Smeghead

    Smeghead New Member

    Joined:
    Oct 6, 2006
    Messages:
    7,108
    Likes Received:
    0
    Location:
    Klingonlandia
    Thanks! This should be stickied btw.
     
  5. SonicYan

    SonicYan Active Member

    Joined:
    Jan 1, 2006
    Messages:
    10,259
    Likes Received:
    0
    Location:
    Orange County, CA
    Wow an educational post! Thanks. :h5:
     
  6. psykosis

    psykosis Go placidly amid the noise and the haste

    Joined:
    Oct 31, 2001
    Messages:
    123,841
    Likes Received:
    157
    Location:
    Listing between sin and salvation
    ifl.

    looks like a great edu at first glance. I'll read it more thoroughly later.
     
  7. wrong1

    wrong1 Member

    Joined:
    Sep 12, 2004
    Messages:
    1,363
    Likes Received:
    0
    Location:
    socal
    good stuff, thanks
     
  8. themolsen

    themolsen New Member

    Joined:
    Sep 29, 2006
    Messages:
    7,414
    Likes Received:
    0
    Location:
    Jacksonville, FL
    cool explanation. I've made a habit out of overexposing my images a bit anyways to help reduce noise, but I never thought about the other aspects. Thanks for the write-up :h5:
     
  9. the Rosswog

    the Rosswog OT Supporter

    Joined:
    May 14, 2002
    Messages:
    5,199
    Likes Received:
    0
    Location:
    Pittsburgh
    a lot of good information here, but one thing i have a big problem with: your example photo of the BMW is still underexposed, and your edited version is even worse. You cant see ANY detail in the shadows, particularly the front grills, and front bumper opening.

    This is a major problem these days... kids online who "know it all" and can't take a decent picture to save their lives.
     
  10. FoolioABC

    FoolioABC New Member

    Joined:
    Jul 18, 2005
    Messages:
    335
    Likes Received:
    0
    i usually just lurk, but this thread has been super educational and i wanted to thank the thread starter. so you know, thanks.

    edit: nevermind read it closer and you've explained it already
     
    Last edited: Jan 20, 2010
  11. themolsen

    themolsen New Member

    Joined:
    Sep 29, 2006
    Messages:
    7,414
    Likes Received:
    0
    Location:
    Jacksonville, FL
    lol yea I just ignored the photo example
     
  12. BeachBoy

    BeachBoy New Member

    Joined:
    Mar 8, 2006
    Messages:
    1,214
    Likes Received:
    0
    Location:
    Calgary, AB
    houston, can't see shit in the blacks on the BMW (we even loose the grill details in front).. unless my work screen is bad.. I can't see the vertical lines in the grill on the last picture.
     
  13. Professor Chaos

    Professor Chaos New Member

    Joined:
    Sep 27, 2004
    Messages:
    21,219
    Likes Received:
    0
    Location:
    Hamilton, Ontario
    Good write up!

    But I have no idea what I'm doing when it comes to "fine tuning the curve" :(
     
  14. upi

    upi OT Supporter

    Joined:
    Aug 9, 2005
    Messages:
    8,776
    Likes Received:
    1
    Thank you.
     
  15. djlogik

    djlogik New Member

    Joined:
    Apr 22, 2004
    Messages:
    2,561
    Likes Received:
    0
    Location:
    Tinley Park, IL
    Nice write up, thanks.
     
  16. Total Xenocide

    Total Xenocide OT Supporter

    Joined:
    Jul 11, 2007
    Messages:
    572
    Likes Received:
    0
    Thanks for taking the time to write that up
     
  17. Ty Webb

    Ty Webb You don't have to go to college. This isn't Russia

    Joined:
    Dec 17, 2004
    Messages:
    10,927
    Likes Received:
    0
    Location:
    Bushwood Country Club
    Thanks for this. Really appreciate the time you put into explaining it.
     
  18. OlafBeserka

    OlafBeserka girls pee pee when they see me OT Supporter

    Joined:
    Jul 5, 2005
    Messages:
    7,485
    Likes Received:
    0
    Location:
    Hella Bay Area
    thanks. good info. needs better examples though
     
  19. nainline6ftw

    nainline6ftw Winter is coming

    Joined:
    Oct 6, 2009
    Messages:
    12,298
    Likes Received:
    0
    Wirelessly posted via wap.offtopic.com (trollphone: Mozilla/5.0 (Linux; U; Android 1.5; en-us; A6277 Build/CUPCAKE) AppleWebKit/528.5+ (KHTML, like Gecko) Version/3.1.2 Mobile Safari/525.20.1)

    I can see the lines in the grilles on both of my monitors and the print. When you're dealing with exposures that subtle they can easily be ruined by resizing and uploading them to Photobucket. At any rate it was a convenient example so take it or leave it.
     
  20. nainline6ftw

    nainline6ftw Winter is coming

    Joined:
    Oct 6, 2009
    Messages:
    12,298
    Likes Received:
    0
    I'm bumping this since I just sent the link to someone
     
  21. cyc1120

    cyc1120 OT Supporter

    Joined:
    Dec 17, 2006
    Messages:
    766
    Likes Received:
    0
    Good stuff. Thanks
     
  22. Girth

    Girth ¯\_(ツ)_/¯ OT Supporter

    Joined:
    Jun 28, 2002
    Messages:
    71,429
    Likes Received:
    109
    Location:
    Houston
  23. pantheR

    pantheR New Member

    Joined:
    Nov 1, 2006
    Messages:
    2,684
    Likes Received:
    0
    Location:
    Washington, DC
    More info on this??
     
  24. jared_IRL

    jared_IRL OT Supporter

    Joined:
    Feb 12, 2006
    Messages:
    17,737
    Likes Received:
    55

    You would think that a cameras sensor records equal amounts of data completely throughout the eposure range, but it doesn't. The way digital cameras record, more than 75% of the cameras available coding data happens in the highlight areas of the sensor. So if you look at your histogram, the right side of the histogram contains 75% the information, and the left side contains 25%. This is why you get tons of noise if you underexpose and image and try and save it in photoshop. There just isn't any data there to pull back, so the camera tries to fake it, and you get noise.

    Here's a longer and probably better explanation...

    http://www.luminous-landscape.com/tutorials/expose-right.shtml
     
  25. adamlewis88

    adamlewis88 New Member

    Joined:
    Dec 2, 2007
    Messages:
    5,392
    Likes Received:
    0
    Location:
    San Francisco, CA
    I really only bother with ETTR when I know Im shooting high ISO to try and keep noise down. Otherwise I dont bother. I appreciate the original post but that last example with the BMW is awful. Yeah there is contrast but its only because those blacks are flat out murdered. Youve got crushed blacks, selective coloring, vignetting, and saturation to 11. :ugh2:

    If youre shooting at high ISO, always try to expose to the right and pull it back in post. It will give you the cleanest image possible.
     

Share This Page