Bit depth?

Discussion in 'Beyond the Basics' started by manaheim, Jul 7, 2008.

  1. manaheim

    manaheim Jedi Bunnywabbit Staff Member Supporting Member

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    So my D300 can shoot at 12 or 14 bit depth.

    Photoshop tells me the images are 16 bit depth, though I assume that's just because Photoshop is designed to handle 8 or 16 and is rounding up... but I don't know.

    I could make the rash assumption that I always want to shoot at the highest bit depth possible, but I'm not sure I can visually see much difference between them.

    What am I missing? Is my monitor just lacking the color range? Is it something somewhat imperceptible? Perhaps something I should be concerned about primarily when printing and not worry otherwise?

    Or... some other thing? :)
     
  2. manaheim

    manaheim Jedi Bunnywabbit Staff Member Supporting Member

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    Wow, 20 reads and not a single reply. So must be a lot of people interested, anyway... :)
     
  3. *Mike*

    *Mike* TPF Noob!

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    Bit depth refers to the tonal range of an image - the number of colors that are able to be represented. Jpg's are only 8-bit. Many cameras shoot 12-bit, with newer bodies capable of 14-bit.

    8-bit files have 256 possible levels (0-255) of red, green, and blue. This results in 167,77,216 (256x256x256) possible combinations of RGB for your files. Now 12-but is able to produce 4096 levels per channel - 68,719,476,736 colors. 14-bit is even higher.

    So, the higher bit-depth you shoot, the more data you have to manipulate. Even though monitors and printers can't reproduce that full spectrum, the data is available when you start to manipulate the image in post-processing. As a result, the file holds up better and you will have less artifacts.

    Bottom line, if you're shooting jpg it doesn't matter, you're restricted to 8-bit. If you convert your RAW's to jpg before you edit, again, it doesn't matter. And in reality, most of the time 8-bit holds up just fine. But, recognize that you're producing more limited files than your camera is capable of... And, if you ever start to heavily manipulate an image, you'll wish you had the higher bit-depth so that the file was "sturdier" in a sense.
     
  4. Bifurcator

    Bifurcator TPF Noob!

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    What Mike said and:


    "I'm not sure I can visually see much difference between them."

    You can't - you're right. You're on an 8 bit (or even 6 bit) monitor but during edits there's more latitude to work with - so edits can happen in 12 or 14 bit that would cause clipping, banding, and etc. in 8 bits.
     
  5. Big Mike

    Big Mike I am Big, I am Mike Staff Member Supporting Member

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    I read an article a few years ago, which summarized this quite well for me.

    Take the histogram of your image...it's a exact graphical representation of the tones/colors in your image. When you adjust the image (a levels adjustment, for example) you are changing many of the pixels. However, the number of pixels is fixed, so when you change some of them, they move to a different spot on the graph, which can leave gaps where those pixels were. You can see this for yourself...do a levels adjustment & close the dialog...then open it up again. The graph will probably have some gaps. It may not be immediately visible in the image, but those gaps can show up as lines or rings where there should be a smooth gradient of color & tone.

    So when you have more bit depth, there is more information and the graph is made up of smaller pieces. So when you make changes, the gaps are smaller, which means that the gradients will be smoother.

    As mentioned, it's not something that is always visible and so not always necessary to worry about but on the other hand, it does make sense to use and keep the highest quality possible.
     
  6. Bifurcator

    Bifurcator TPF Noob!

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    Yup, it may or may not be long till 12, 14, or 16 bit display devices are available. Printers already are for the most part. (I think - Helen B or others would know more.)
     
  7. manaheim

    manaheim Jedi Bunnywabbit Staff Member Supporting Member

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    This is great info, guys. I appreciate it.

    I'm starting to think maybe I should be processing my images to something other than JPEG... maybe PNG, since it appears it is 24 bit. I always keep the RAW files anyway, but I double backup my "album" where I keep all the images I have corrected as a "just in case I lose a DVD of RAWs" kind of thing...

    Hmmm...

    This is a lot to think about in general.

    Thank you, all.
     
  8. manaheim

    manaheim Jedi Bunnywabbit Staff Member Supporting Member

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    ooo... NASTY. I just quickly tried to open a RAW image as 16 bit and save it as a PNG. 55 meg instead of 5. Ok that's SO not going to work. LOL

    Question... based upon what you guys have said, it sounds like if I opened the image in Photoshop as a 16 bit image, made my various corrections, and then converted it to an 8 bit image and THEN saved it that I would be better off than working with it as 8 bit to begin with... yes?

    If so, then maybe I should do that and plan to re-correct the image from the RAW when printing or working on higher-quality monitors down the road.
     
  9. RyanLilly

    RyanLilly No longer a newbie, moving up!

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    This is my understanding, Also the only reason to save as 8 bit is for jpeg, other than that I stay in 16bit files. If your printer can accept 16 bit tiff, that would be the highest quality, if you don't mind the huge files, although i think some printers software just converts them to 8 bit before printing, though I'm not sure.
     
  10. Bifurcator

    Bifurcator TPF Noob!

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    Use DNG (Digital Negative) format. It should be about 1/3 or 1/4 the size of a PNG.


    Yes indeed.


    Or just save DNG. Either way. I guess it depends on the number of images you have and that you plan to later "re-correct". If it's even more than a few though I would do the DNG thing!

    Download pages:
    Have fun!
     
  11. Mav

    Mav TPF Noob!

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    This post has been approved by the "official defender of JPEGs. :lol:


    Yes, 8-bit JPEGs are not as 'sturdy' if you plan to do a lot of manipulation, but most of the time they do hold up just fine. :thumbup:
     
  12. manaheim

    manaheim Jedi Bunnywabbit Staff Member Supporting Member

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    Yeah, I did the DNG thing for a bit when I didn't have CS3. (did the converter from the RAW...) I think, however, the DNGs are roughly the same size as the NEFs... ~15megish for my camera.
     

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