Over expose or under expose?

Discussion in 'Canon EOS' started by danielransom, Oct 29, 2006.

  1. Is it better to sightly over expose or slightly under expose a shot? I have heard discussion on both sides
    as to which is better. Both sides say that their technique carries more info. I shoot with a Canon 30D.
    Could this be another one of the differences between CMOS and CCD sensors?
     
  2. This may sound a bit smart-alecky, but why not properly expose? Seriously though, If you plan to post process the photo, over-expose. If you plan to leave it as-is, then under expose.
     
  3. Very often, overexposed means blown out highlights and by that definition, anything overexposed (ie, pixel value greater than 255 255 255) will be pure white and no info can be recovered from it. >> Result: you are screwed.

    Things underexposed does not mean pixel value of 0 0 0 so info can be extracted out. If you increase the exposure digitally, you end up also amplifying the noise so the noise will be much worse for that particular ISO that you were using.

    However, the real reality depends on the situation. if the over exposed section is a street light in the background, that's perfectly find. Or if the over exposed region is some cloud that's not important and does not add much to the photo, then go ahead and over expose it if that's what you need to bring the rest of the photo to proper exposure. (i.e. overexposed useless highlights so that the main subject is properly exposed).

    If the main subject is over exposed to 255 255 255, then you are screwed. In this case, better to underexpose.

    Just to throw this out there. If you shoot raw, you have about another stop to play with and can recover a 255 255 255 over exposed section if it's only very slightly overexposed past 255 255 255.
     
  4. Shoot RAW, and expose to the right. The best exposure is generally one which is as far right as possible, without clipping. If you err on the side of underexposure, you lose dynamic range and get more noise. If you err on the side of overexposure, you get clipped highlights, which cannot be recovered.
    If you shoot JPEGs, aim for an exposure which makes the JPEG look the way you want it. Given the limited bit depth of JPEGs and the use of lossy compression, you are best off if you can avoid having to do any editing, so try to get it right the first time.
     
  5. Why overexpose or shoot the histogram to the right, noise. That's why, to minimize noise you need to overexpose the highlights to minimize noise in the shadows. When do I use this technique? Shooting at the rink photographing skaters. I can't picture using this technique other than a low light situation.

    Gerry
     
  6. A perfect bell curve histogram that touches neither end...
     
  7. Really? What if you're photographing a bride in her white dress, or the groom in his black tuxedo?
     
  8. Avoid over-exposure of digital images that results in completely blown out highlights - it
    is difficult or
    impossible to get back detail here.

    There will be shots in which your sensor cannot handle the full range of brightness, in
    which case you have to choose what you will lose. In general (though I can imagine
    exceptions) I'd rather see a shadow go completely black than see highlight areas go totally
    white.

    Shoot RAW since you can often recover some detail that would be lost in .jpg. You may be
    able to get
    back some detail from those shadow areas.

    Other useful tricks include doing two separate
    RAW conversions - one for bright portions of the image and another for the shadows -
    and combining them.

    As someone pointed out, keeping the curve from being lopped off at either end of the
    histogram is a Good Thing.
     
  9. If you shoot RAW the general rule is to expose to the right as far as possible without clipping
    your highlights... for a more detailed explanation as to why this is a good idea, read here...

    http://www.luminous-landscape.com/tutorials/expose-right.shtml
     
  10. Something I've just been trying to get my head around: It really depends on the shot. The camera assumes your scene is neutral grey brightness, but that's not always the case. If I'm shooting a shadowy dusk scene, and I want it to look the way I see it, I should underexpose, a stop or two. If I'm shooting bright snow and skiers scene, I should overexpose a stop or two.
     
  11. Properly expose. It's not all that difficult.
     
  12. My vote is that if you are shooting raw then expose as far to the right as you can WITHOUT clipping the highlights. If you are looking for .jpg straight out of the camera then most situations call for slightly underexposing (1/3 to 2/3 stop). This inst ideal "shooting raw is" but you get good shots with no post processing most often that way.
     
  13. Lots of superstition here, lots of misinformation...someone even wrote that blocked up shadows (value 0,0,0) can be recovered! What cr@p. The fact is, blown highlights (4,095, 4,095, 4,095) and blocked up shadows (0,0,0) both are gone forever. For RAW shooting, 12-bit color, 2 to the power of 12 is 4,096 levels of brightness. 4,096 to the power of 3 is 68.7 billion color combonations.

    If you shoot raw then over expose WITHOUT blowing highlights on the SUBJECT of your composition. It's not true that one must never blow high lights. This is a falisy...when it comes to the subject then one must be careful. This is more a guideline then a hard and fast rule.

    You need to realize that more then half of the image detail lives in the last 1.5 to 2 stops (rightmost) of the historgram, so that means that if your shadows are value (0,0,0) then just like blown highlights (4,095, 4,095, 4,095) they are not recoverable. And since more then half of the image detail lives in the 1 - 2 rightmost stops of the histogram then it is better for the shadows if one over exposes, but again not to the point of blowing the highlights on the subject of the composition. Once in post processing one can pull back the historgram left to get the shadows in their correct brightness.

    As for shadow detail, the left most stop of the histogram contains only 128 brightness levels (4,095 when shooting raw across the entire histogram)! A pitiful small amount, but if you expose to the right you'll have a better chance of saving the shadow and even mid tone details.

    A good exposure is not necessarily one where the data just touches the right and left extremes of the histogram....another falisy because this does not guarentee that your subject is exposed properly...what exposure is right is as unique as each composition...but in general, for highest image quality, shoot only raw, and expose to the right but watch the highlights.

    The biggest mistake users of DSLRs make is to think that just because the image exposure looks great on the LCD display on the back of the camera, that the exposure is great. WRONG...this is not necessarily true and judging exposure this way will often make for bad exposed pictures. Better to use the image on the back LCD ONLY for judging the COMPOSITION....and for judging the exposure ONLY use the histogram.

    Another mistake that DSLR users make is trying to get a raw image to look "right" at the time the shutter is released....this mistake will often cost the image precious image detail because the photog tries to make the image look great via the display on the back of the camera....but this often will cause the photog to NOT expose to the right because doing so could make the image look washed out. But what he does not realize is that the image is SUPPOSED to often look washed out. Better to expose to the right, then pull back during post processing. If your raw image looks "great" on the back of the camera's LCD, then the photog probably didn't expose to the right, thereby causeing added noise, and the LOSS of shadow image detail.

    Remember, raw images are supposed to look a bit washed out, flat, and lacking razor sharp focus....this is the part that really throws a lot of DSLR raw shooters off. During the required post processing, one pulls back during raw conversion, and this is done with as much image detail as possibly saved during exposure in the camera.

    One last thing...since the dynamic range of all our DSLR's are pitifully too narrow, when you compose a picture you will often be in a position to have to compromise.,...do you expose for the highlights, the shadows? Again, expose to the right, and if non-subject areas of the composition get blown so be it...this is not necessarily wrong....just make sure your subject gets exposed properly and if doing so blows the background, so be it.

    So if you shoot raw, and you expose to the right, and then you get home from your trip and most of your 1,000 images of Paris are washed out, flat, fuzzy, and just plain blah, then rejoice because this means you probably exposed those images perfectly, and these images will be an excellent foundation for most excellent post processing results!

     
  14. check this out...

    http://forums.dpreview.com/forums/read.asp?forum=1032&message=20664428
     
  15. I agree 100% with everything Pavel said.

    Just get out there and try it. One of the beauties of digital is instant feedback. I come from a film background where you had to write down all your exposure data then wait to process the film. Then you would print it and put all together to see what worked. Now just look at the ExF data and look at the image you took just moments before.
     
  16. Everything he says but:

    "someone even wrote that blocked up shadows (value 0,0,0)"

    If you took the time to read my sentence clearly you wouldn't be making this claim.
     
  17. Thanks to everyone. This site always has great input. My consideration is how to get the
    most information in each shot, and not really a problem with basic exposure. I can
    regularly expose properly in almost every situation except extreme dark and light. Very
    bright days while using flash to avoid shadows; or small, dark rooms while facing a
    window, also using flash, like facing the street while shooting in a storefront. Both of
    these situations are real life occurances with me. The key part of the equation would be if
    I was shooting in manual in those conditions and relying on viewing the monitor to
    determine exposure. This is of particular consideration if I am shooting RAW and JPEG
    simultaneously.
     
  18. Wow, seems this "simple' question has touched such a nerve, or opened a greater vein.
    You gotta love it. Please keep up the input.
     
  19. Weiyang, I stand corrected, however uderexposing is a really bad idea....like I wrote earlier, there it about 128 levels of brightness in the most left stop of the histogram....so if you underexpose, even if shadows are not blocked, guess what? You loose tons of precious image detail....better to over expose, pull the shadows to the right, then at time of raw conversion, pull them back...that way you get the most image detail information possible.

    When underexposing, just because the histogram shows no blocked shadows does not mean that precious image detail is preserved....often it is not, nor can it be recovered...again the most left stop of the histogram carries very little data.....the 4,096 levels of brightness are not destributed linearly across all the stops of the histogram.
     

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