Site Sponsors
Page 2 of 2 FirstFirst 1 2
Results 51 to 76 of 76

Thread: Canon 1DX and implications for MF

  1. #51
    Super Duper
    Senior Member
    Shashin's Avatar
    Join Date
    May 2011
    Location
    Florida, USA
    Posts
    4,498
    Post Thanks / Like
    Images
    141

    Re: Canon 1DX and implications for MF

    60MP in a 35mm sensor. Hmm... You do know that photography is light dependent and not plagued by it. Pixels actually having a surface area is important. It is all about catching photons.

  2. #52
    madmanchan
    Guest

    Re: Canon 1DX and implications for MF

    Don't want to get too sidetracked here ... but Jack and Lars are correct about the capture dynamic range of a digital sensor.

    Yes, it is true that from a representation / storage point of view, the dynamic range and bit depth are independent. The former is the contrast (height of stair case) and the latter is the # of steps.

    However ...

    A digital sensor is a linear capture device, so the bit depth is therefore directly related to the maximum possible dynamic range that can be captured. Remember, a linear device means that 2x the amount of light (# of photons) captured translates to 2x the digital image value. For example, a sensor with a 12-bit ADC represents the brightest recordable pixel value at 4095. One stop below that (half the light) is ~2048. Two stops below white (1/4 of the light) is ~1024, then ~512 for 3 stops, then ~256 for 4 stops, etc. all the way till we reach the minimum representable value (the integer 1), which is 12 stops below the maximum value of 4095. So, there is no way to capture a scene of, say, 14 stops, because 14 stops below 4095 is ~0.25 (less than 1).

    What many folks here are thinking of is the output dynamic range of an image (rather than the input or capture dynamic range). Certainly it is true that one can use tone curves, local dodging/burning, gamma encoding, etc. to distribute tonal values however you wish, and use however many bits of precision you want to store the results. For example, you can choose to tone-map an image into 1 stop (really low contrast!) and use 16 bits to represent it. But this is a completely separate matter from the capture dynamic range (i.e., what the sensor is capable of holding).

  3. #53
    Super Duper
    Senior Member
    Shashin's Avatar
    Join Date
    May 2011
    Location
    Florida, USA
    Posts
    4,498
    Post Thanks / Like
    Images
    141

    Re: Canon 1DX and implications for MF

    Quote Originally Posted by madmanchan View Post
    A digital sensor is a linear capture device, so the bit depth is therefore directly related to the maximum possible dynamic range that can be captured. Remember, a linear device means that 2x the amount of light (# of photons) captured translates to 2x the digital image value. For example, a sensor with a 12-bit ADC can represent the brightest pixel value at 4095. One stop below that (half the light) is ~2048. Two stops below white (1/4 of the light) is ~1024, then ~512 for 3 stops, then ~256 for 4 stops, etc. all the way till we reach the minimum representable value (the integer 1), which is 12 stops below the maximum value of 4095. So, there is no way to capture a scene of, say, 14 stops, because 14 stops below 4095 is ~0.25 (less than 1).
    ???? Now who is confusing the file with the signal?

    If DR has a range of 14 stops, I can divide/bin that into any bit depth. The top number would be the peak signal and regardless of bit depth, the peak signal is the same, just a different value assigned to it. Only contrast index, for want of a better term, determines the actual difference in exposure value between two levels. To say the difference between levels 2048 and 4095 is one stop would be completely wrong or at least unknown until you can do some calculations. The sensor response may be linear, but the length is not fixed and bit-depth can be distributed along it no matter the length.
    Last edited by Shashin; 19th October 2011 at 09:58.

  4. #54
    madmanchan
    Guest

    Re: Canon 1DX and implications for MF

    If DR has a range of 14 stops, I can divide/bin that into any bit depth.
    Yes, you can, but the sensor cannot.

    To say the difference between levels 2048 and 4095 is one stop would be completely wrong or at least unknown until you can do some calculations.
    It turns out I do these calculations for a living.

    Suppose I take a picture of an object and it shows up in the original (linear Bayer mosaic) raw data as 4095. If I re-take the picture with half the exposure (e.g., close down 1 f-stop, or half the exposure time), then the pixel values of that object in the 2nd image will be 2048 -- i.e., half. You can replace these example numbers with any specific values you wish. The point is that it's a direct linear relationship in the original raw capture data. So, 2x the exposure means 2x the raw image pixel values ... half the exposure means half the raw pixel values. I have checked this property for many, many cameras (from compacts to MFDBs).

  5. #55
    Super Duper
    Senior Member
    Shashin's Avatar
    Join Date
    May 2011
    Location
    Florida, USA
    Posts
    4,498
    Post Thanks / Like
    Images
    141

    Re: Canon 1DX and implications for MF

    Quote Originally Posted by madmanchan View Post
    Yes, you can, but the sensor cannot.



    It turns out I do these calculations for a living.

    Suppose I take a picture of an object and it shows up in the original (linear Bayer mosaic) raw data as 4095. If I re-take the picture with half the exposure (e.g., close down 1 f-stop, or half the exposure time), then the pixel values of that object in the 2nd image will be 2048 -- i.e., half. You can replace these example numbers with any specific values you wish. The point is that it's a direct linear relationship in the original raw capture data. So, 2x the exposure means 2x the raw image pixel values ... half the exposure means half the raw pixel values. I have checked this property for many, many cameras (from compacts to MFDBs).
    Well, naturally the file will change those values by a factor of two. You have changed the exposure by a factor of two. But what we are talking about is the scene luminance range and the DR of the sensor. What you cannot tell me is if the luminance difference in the scene is actually a factor of two.

    I do scientific imaging and use all kinds of cameras. It is not a simple thing to get subject luminance values from images.

  6. #56
    madmanchan
    Guest

    Re: Canon 1DX and implications for MF

    I was using the in-camera exposure setting as an example.

    But the same holds true for natural scene luminance range, and is actually pretty easy to check using a spot meter (I use a telespectroradiometer such as the Photo Research devices, but simpler devices will work too). Just measure the radiance at a spot and take a picture with the camera. Do the same thing for a darker (or brighter) spot. Compare the ratio of the radiances with the ratio of the recorded digital raw values. They will be the same.

  7. #57
    Super Duper
    Senior Member
    Shashin's Avatar
    Join Date
    May 2011
    Location
    Florida, USA
    Posts
    4,498
    Post Thanks / Like
    Images
    141

    Re: Canon 1DX and implications for MF

    Well, the ratio will stay the same. Afterall, the slope is linear (but the angle unknown). However, the signal can still be binned into any bit-depth for any DR and the tests you do will show the same relative changes in your tests (but it does not indicate actual luminance levels)--I can assign 4095 to the peak signal just as I can 16,535. Changing the bit depth will not change the DR of any particular sensor--signal determines DR. Bit depth comes from ADC, it just bins the analog signal into the levels. A signal has no bits, it is simply the electrical response from the photosite. The ADC need to convert that into numbers and the bit depth is simply the scale it uses, but my coffee cup is not taller in millimeters than it is in centimeters because it has more of them.

  8. #58
    madmanchan
    Guest

    Re: Canon 1DX and implications for MF

    Shashin, I am not saying changing the bit depth of the ADC fundamentally changes the photon capturing properties of the sensor. I am saying that the bit depth of the ADC places a fundamental limit on the linear dynamic range of the scene that can be captured. If a scene contains a very bright area, I can choose my in-camera exposure such that, after conversion to a digital value, it will map to the maximum representable value (e.g., 4095 for a 12-bit system). If that same scene contains a dark area -- say, 8 stops darker than the bright area -- then in the same picture it will map to a digital value that is 8 stops lower (e.g., ~16 for a 12-bit system). If that same scene contains an even darker area -- say, 15 stops darker than the bright area, then it cannot be represented.

    The sensor ADC does not simply "bin" the analog signal into the digital levels. It is not free to scale the analog signal into however many bins it wants. There is a direct linear relationship between the magnitude of the analog signal and the resulting output digital level. If you have 2x the radiance coming from your scene, you'll have 2x the # of photons captured by the pixel, 2x the magnitude of the analog signal, and 2x the resulting digital level.

    If you don't believe me, you can easily verify this for yourself by taking spot readings of the radiance levels in the scene (like I mentioned earlier, telespectroradiometers are great for this type of work). Then take a picture in raw mode and study the digital raw levels (you can use dcraw or other software tools for this). Thus you can establish the relationship between the absolute radiance of a spot in the scene and the corresponding raw level, which you'll find to be linear ...

  9. #59
    Senior Member Graham Mitchell's Avatar
    Join Date
    Nov 2007
    Location
    London/Kiev
    Posts
    1,079
    Post Thanks / Like

    Re: Canon 1DX and implications for MF

    Maybe this will help people to understand. Here is a photo of a subject with 17 stops of dynamic range, yet it is an 8-bit image.


  10. #60
    madmanchan
    Guest

    Re: Canon 1DX and implications for MF

    Yes, Graham, but those aren't the actual values from the raw file ...

    As I mentioned earlier, a rendered image (like the example you posted) can indeed represent however many stops you want with whatever bit depth you want. However, the original raw data in a digital capture can't hold more stops than the bit depth of the sensor's ADC.

  11. #61
    Super Duper
    Senior Member
    Shashin's Avatar
    Join Date
    May 2011
    Location
    Florida, USA
    Posts
    4,498
    Post Thanks / Like
    Images
    141

    Re: Canon 1DX and implications for MF

    madmanchan, can you show that all n-bit cameras have the same DR? (I understand there is a limit to information, but you are suggesting DR is limited to bit depth.)

  12. #62
    Senior Member Lars's Avatar
    Join Date
    Nov 2007
    Location
    Sunnyvale, California
    Posts
    1,811
    Post Thanks / Like
    Images
    19

    Re: Canon 1DX and implications for MF

    Quote Originally Posted by madmanchan View Post
    It turns out I do these calculations for a living.
    Me too.
    Monochrome: http://mochro.com

  13. #63
    Super Duper
    Senior Member
    Shashin's Avatar
    Join Date
    May 2011
    Location
    Florida, USA
    Posts
    4,498
    Post Thanks / Like
    Images
    141

    Re: Canon 1DX and implications for MF

    So why can an Alpha 77 have a 13.2 EV DR and an E-P3 have a 10.1 EV DR? They are both 12-bit cameras.

  14. #64
    Senior Member Graham Mitchell's Avatar
    Join Date
    Nov 2007
    Location
    London/Kiev
    Posts
    1,079
    Post Thanks / Like

    Re: Canon 1DX and implications for MF

    Quote Originally Posted by madmanchan View Post
    Yes, Graham, but those aren't the actual values from the raw file ...

    As I mentioned earlier, a rendered image (like the example you posted) can indeed represent however many stops you want with whatever bit depth you want. However, the original raw data in a digital capture can't hold more stops than the bit depth of the sensor's ADC.
    ok, but here is the quote which started this whole discussion: "Bit-depth refers to the number of luminance levels an image is binned into. It has nothing to do with dynamic range which is related to how much signal can a photo site absorb. So a 16-bit image does not automatically give you more dynamic range."

    But I see where the confusion came from. Yes, you need a 16 bit raw file in theory to capture a scene with 15 stops of DR, but that point is moot as we don't have sensors with 15 stops of DR, so the 16 bit raw file is a waste, which was shashin's original point.

    p.s. raw files are often not unadulterated ADC output, but that's another matter entirely

  15. #65
    Senior Member Lars's Avatar
    Join Date
    Nov 2007
    Location
    Sunnyvale, California
    Posts
    1,811
    Post Thanks / Like
    Images
    19

    Re: Canon 1DX and implications for MF

    Quote Originally Posted by Graham Mitchell View Post
    But I see where the confusion came from. Yes, you need a 16 bit raw file in theory to capture a scene with 15 stops of DR, but that point is moot as we don't have sensors with 15 stops of DR, so the 16 bit raw file is a waste, which was shashin's original point.
    Well put (although I read shashin's original point differently, perhaps mistakenly). And hopefully that's how camera manufacturers reason when they decide on bit depth of the processing pipeline. Although it baffles me a bit why in a computer it makes sense to cap A/D and calculation pipeline to 14 bits, almost all chips seem to work in bytes these days.
    Monochrome: http://mochro.com

  16. #66
    madmanchan
    Guest

    Re: Canon 1DX and implications for MF

    Hi Shashin, generally N-bit cameras have at most N stops of DR, but in practice less than N stops because of (read) noise. In other words, the ADC bit depth places an upper limit on the recordable scene dynamic range, but it's not the only limit. The noise floor of the sensor is the main other limit.

    The recent Sony cameras like the A77 use a 12-bit compressed internal format to store the image values, but the actual linear raw data is 14 bits.

  17. #67
    Member
    Join Date
    Sep 2011
    Posts
    77
    Post Thanks / Like

    Re: Canon 1DX and implications for MF

    I fear I am getting a little lost in the bit -depth discussion. Is the gist
    of the answer that current sensors can NOT generate sufficient tonal
    range as to need 16 bit? Is it the consensus then that 16 bit AD is NOT
    really needed (because it can't really be used) and hence a 14 bit
    path is just as good (for now) as a 16 bit?

    If so, then why (with the possible exception of the pentax 645D) are
    the medium format cameras 16 bit and the 35 mm 14 bit? Is this
    merely marketing?

    Thanks for clarifying and educating!!

    craig

  18. #68
    Senior Member Lars's Avatar
    Join Date
    Nov 2007
    Location
    Sunnyvale, California
    Posts
    1,811
    Post Thanks / Like
    Images
    19

    Re: Canon 1DX and implications for MF

    This whole discussion about bit depth and DR of course assumes a linear sensor and linear processing pipeline. As far as I know, this holds for almost all digital cameras on the market. There are however other possibilities.

    Howtec (and now Aztek) drumscanners have an A/D converter that can be loaded with a response curve, so effectively you can place the bins where you need them the best, for example use a gamma response curve to push more bins towards the shadows. At gamma 2, 14 bits would be sufficient in terms of DR even for more extreme HDR sensors.

    Or perhaps we'll see floating point A/D converters in cameras eventually, which would make this discussion about bit depth a bit moot. For imaging purposes 16-bit "half" floats are quite sufficient.
    Monochrome: http://mochro.com

  19. #69
    Super Duper
    Senior Member
    Shashin's Avatar
    Join Date
    May 2011
    Location
    Florida, USA
    Posts
    4,498
    Post Thanks / Like
    Images
    141

    Re: Canon 1DX and implications for MF

    All I was trying to say was that adding 16-bit ADC was not suddenly going to let a camera capture anymore DR than the sensor is going to provide. 16-bit seems to be brought out as some kind of silver bullet that will do amazing things to expand the sensor signal.

  20. #70
    Sr. Administrator Jack's Avatar
    Join Date
    Oct 2007
    Location
    Los Altos, CA
    Posts
    10,486
    Post Thanks / Like
    Images
    1031

    Re: Canon 1DX and implications for MF

    Quote Originally Posted by Shashin View Post
    All I was trying to say was that adding 16-bit ADC was not suddenly going to let a camera capture anymore DR than the sensor is going to provide. 16-bit seems to be brought out as some kind of silver bullet that will do amazing things to expand the sensor signal.
    We never said that either. Eric explained it very well, and not wanting to beat a dead horse, but the basic thing to take away from this is that in addition to color fidelity, bit-depth IS related to total usable DR, and more is better; you cannot generate a true 17 stops of DR from an 8-bit file, the math will not allow it. What you can do is what Graham showed, PERCEPTUALLY render (compress) 17 stops in 8 bits, but if you read those values you will see they are not true full stops, but at at best rather 8/17ths or roughly 1/2 of a stop increments of light values.
    Jack
    home: www.getdpi.com

    "Perfection is not attainable. But if we chase perfection, we can catch excellence."

  21. #71
    Workshop Member Wayne Fox's Avatar
    Join Date
    Nov 2009
    Location
    Draper, Utah
    Posts
    871
    Post Thanks / Like
    Images
    134

    Re: Canon 1DX and implications for MF

    Quote Originally Posted by craigrudlin View Post
    I fear I am getting a little lost in the bit -depth discussion. Is the gist
    of the answer that current sensors can NOT generate sufficient tonal
    range as to need 16 bit? Is it the consensus then that 16 bit AD is NOT
    really needed (because it can't really be used) and hence a 14 bit
    path is just as good (for now) as a 16 bit?

    If so, then why (with the possible exception of the pentax 645D) are
    the medium format cameras 16 bit and the 35 mm 14 bit? Is this
    merely marketing?

    Thanks for clarifying and educating!!

    craig
    I think most of the MF backs are actually 15 bit, not 16. But rather than compressing the data down to 14 bit, they expand to 16 bit since that's what most use the raw processing pipeline. As mentioned, bit depth of the resulting file isn't related to the bit depth sensitivity of the sensor.

    Does it make a difference? As one who shoots several formats (NEX5, M9, 5D Mark2, IQ180) I do know I can pull more shadow details with less noise for the MF files than anything else, and I really don't feel I need to bracket unless the situation is extreme (such as sun in the image) with the MF. I have intentionally underexposed by 4 f-stops (shooting at ISO 35 but with the same settings I would use if I was at ISO 400) and have processed the resulting file to give identical results to one exposed at 400. I was doing this to research the idea that changing ISO in a Phase back doesn't really do anything to help overall quality, but was rather shocked to see files with literally not much there process out to be equal in quality to those that looked normal.
    wayne
    My gallery

  22. #72
    Senior Member Thierry's Avatar
    Join Date
    Jun 2011
    Location
    Switzerland
    Posts
    329
    Post Thanks / Like

    Re: Canon 1DX and implications for MF

    +1

    Quote Originally Posted by Graham Mitchell View Post
    "Bit-depth refers to the number of luminance levels an image is binned into. It has nothing to do with dynamic range which is related to how much signal can a photo site absorb. So a 16-bit image does not automatically give you more dynamic range."
    Quote Originally Posted by Shashin View Post
    All I was trying to say was that adding 16-bit ADC was not suddenly going to let a camera capture anymore DR than the sensor is going to provide. 16-bit seems to be brought out as some kind of silver bullet that will do amazing things to expand the sensor signal.
    Thierry Hagenauer
    [email protected]

  23. #73
    Member
    Join Date
    Sep 2011
    Posts
    77
    Post Thanks / Like

    Re: Canon 1DX and implications for MF

    Some clarification, please...

    So, if two sensors both have the same dynamic range, but one is "piped" into 14 bit and the other 16bit, the one that is 16 bit should allow a greater
    tonal range and hence the image will appear to have more tonal range
    and more of the "micro contrast" or 3-D appearance that characterizes
    MF and larger format prints?

  24. #74
    Sr. Administrator Jack's Avatar
    Join Date
    Oct 2007
    Location
    Los Altos, CA
    Posts
    10,486
    Post Thanks / Like
    Images
    1031

    Re: Canon 1DX and implications for MF

    Quote Originally Posted by craigrudlin View Post
    Some clarification, please...

    So, if two sensors both have the same dynamic range, but one is "piped" into 14 bit and the other 16bit, the one that is 16 bit should allow a greater
    tonal range and hence the image will appear to have more tonal range
    and more of the "micro contrast" or 3-D appearance that characterizes
    MF and larger format prints?
    Not necessarily. If the sensor has a true DR of MORE than 14 stops, then yes.

    The thing to try and understand is how a digital sensor renders an image. This is an oversimplification, but consider it two distinct parts: a digital sensor that can ONLY respond to Luminance values in a linear fashion, a Bayer filter to render Hue, and then the combined effects of both of those render Saturation, giving you basically an HSL color model to work with. So while bit-depth certainly is important to color fidelity, it also directly relates to luminance read values coming off that monochrome sensor. Here since it's linear, to be most efficient it has to use half of its bits to render it's brightest value, then one stop down is half of that, one more stop down, half of that again, so on. In 8-bit parlance the sensor needs 128 of its bit per channel to render the top value, one stop down it needs 64, one more down it needs 32, then 16, 8, 4, 2 and finally 1. Counting those values you get a maximum of 8 stops of accurate LINEAR DR rendered. Anything more shown in 8-bits has to be compressed, which may well generate a PERCEPTUALLY pleasing result, but not an accurate linear rendering of total DR. Again, once you understand how a digital sensor generates luminance separate from hue values, you can begin to understand the limitations bit-depth places on linear luminance readouts.
    Jack
    home: www.getdpi.com

    "Perfection is not attainable. But if we chase perfection, we can catch excellence."

  25. #75
    Not Available
    Join Date
    Jul 2009
    Location
    New York
    Posts
    1,864
    Post Thanks / Like

    Re: Canon 1DX and implications for MF

    Meh. Canon FF 35mm sensor <> MF.

  26. #76
    Member
    Join Date
    Jan 2010
    Location
    Munich/NYC
    Posts
    29
    Post Thanks / Like

    Re: Canon 1DX and implications for MF

    Quote Originally Posted by Double Negative View Post
    Meh. Canon FF 35mm sensor <> MF.

Tags for this Thread

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •