Dynamic range of some model cameras

davesrose wrote in post #3660197
Tonal range of an image can only be manipulated within the dynamic range of the image file itself. In a classical RGB color space, that's 256 shades of tone. Jpeg has a total of 256 luminosity levels to distribute....12bpc RAW has a total of 4092. Tom's examples are proof that jpeg has more limited tonal range then RAW....and here's a bit more:

Here are the terms for the different DRs of photography:

http://en.wikipedia.or​g/wiki/Exposure_range

I just found this article which describes the differences in contrast range and what that means in F stops between the different bit depths:

http://www.cambridgein​colour.com/tutorials/d​ynamic-range.htm

Could someone please explain something to me.

I thought that for an 8 bit system 0 represented pure black and 255 represented pure white.

I also thought that for a 12 bit system 0 would represent pure black and 4091 would represent pure black.

Neither system seems to go darker than pure black or lighter than pure white. The 12 bit system just gives finer gradients between those extremes.

My understanding must be wrong if the 12 bit system has more tonal range than the 8 bit system since it must go darker than pure black in the 8 bit system and/or lighter than pure white in the 8 bit system.

Would someone please explain this to me? Thanks.

ScottE wrote in post #3665069
Could someone please explain something to me.

I thought that for an 8 bit system 0 represented pure black and 255 represented pure white.

In RGB, 0 is black and 255 is white.....256 total values.

ScottE wrote in post #3665069
I also thought that for a 12 bit system 0 would represent pure black and 4091 would represent pure black.

HDR formats actually express values going from black to white from 0 to 1 (and all values are then a floating point). So they can go 16bpc or 32bpc. TIF can either be 16bpc or 32bpc (and fewer apps can read 32bpc). A very popular 32bpc format for 3D is OpenEXR. Developed by LucasArts....that supports full bit depths and an unlimited number of channels.

Bits/channel does represent the amount of contrast or tone for that channel: 12 bit (2 to the 12) is 4096 shades of values (black to white). Full 32bpc is 4.29 billion shades of tone for each channel. Might seem like a ludicrous amount.....but 3D programs need them to represent the true luminosity that you would get in any environment.

http://www.openexr.com​/about.html

As I've learned now, digital cameras are currently limited to "about" 12bpc.....the image file's tonal range is the range of values in its color channel. But the overall DR of the photo is contingent on the amount of light (or stops) that the sensor can capture, how well the processor can distribute those luminosities to values in a channel, and what bit depth your image is set at. A 8bpc image can have a full tonal range without any blown highlights and good mid-tones if the camera was able to capture the entire DR and fit it in that particular bit depth. Having a higher bpc RAW file will give you the full range of the processor and also give you more levels for for PP.

ScottE wrote in post #3665069
Could someone please explain something to me.

I thought that for an 8 bit system 0 represented pure black and 255 represented pure white.

I also thought that for a 12 bit system 0 would represent pure black and 4091 would represent pure black.

Neither system seems to go darker than pure black or lighter than pure white. The 12 bit system just gives finer gradients between those extremes.

My understanding must be wrong if the 12 bit system has more tonal range than the 8 bit system since it must go darker than pure black in the 8 bit system and/or lighter than pure white in the 8 bit system.

Would someone please explain this to me? Thanks.

I think the answer to that is that the camera is making an approximation of black and white. True black is no light what so ever and true white doesn't really exist in that you can always increase the amount of light (well at least until everything starts to melt). When the camera shows black it simply means that it wasn't able to record any light and when it's white it means that it can't record any more light. The maximum and minimum levels can obviously be altered by changing the Aperture, Shutter Speed, ISO etc however you can only do one at a time.....

If the camera has a wider dynamic range it simply means that the range that it can capture between black and white is larger.

Hope this makes sense.
Jason.

davesrose wrote in post #3662651
And you keep ignoring the fact that the captured data becomes RGB.....we are not seeing an image that has more green then red or blue. You're still completely ignoring color theory!!!

Just because an image is displayed in RGB doesn't mean you can't use the extra green information. You collect more green information, because of the fact that the eye is biased towards green sensitivity; then, when you create the RGB image, you have the information distributed in the manner which best suits the human eye.

Think of it this way: a RGB image is actually a composite of three individual images: one red, one green, and one blue. Each of these images is a single color, with each pixel simply having an intensity value (brightness/luminosity​). Since you had more green photosites than red and blue, your green image is more detailed, and more accurate a representation of the actual scene than the red and blue images. This is done because you eye is more sensitive to green, so having the same amount of detail in the other channels as the green channel is essentially a waste of data (or, more accurately, a sub-optimal use of resources).

Again, the image is RGB, but that does NOT mean that the extra green information is not used; it is, actually, very significant in the formation of the composite image, during the demosaicing process, as it allows a higher degree of accuracy of green at each pixel.

"Digital camera raw files contain the pixel data from a rectangular image sensor, the modern equivalent of traditional film, usually at 12 or 14 bits per sensor bucket. The sensor is almost invariably overlaid with a so-called Bayer filter, consisting of a mosaic of red, blue and green filters in alternating rows of RG and GB. Given that three colors fit uncomfortably in a rectangular grid, green was chosen to be doubly present, since the human eye is more sensitive to it. Green also often serves as the luminance channel, and as the dominant channel for in-camera black-and-white conversions. To retrieve an image from a raw file, this mosaic of data must be converted into a full RGB image. This is known as demosaicing, but is sometimes referred to as digital development"

You're reading too far into this statement. Note that in the sentence that they state "for in-camera black-and-white conversions."

See my statement above. Just because the final image is not green-dominant doesn't mean that the extra detail is not used, nor does it mean that our eyes can't see the extra detail in the green channel.

You selectively quote statements, and then selectively take information from them. In your quoted statement above, it specifically states that green was chosen to be doubly present, because the human eye is more sensitive. For clarity, I quote (again):

"Given that three colors fit uncomfortably in a rectangular grid, green was chosen to be doubly present, since the human eye is more sensitive to it."

Please, tell me again that the human eye was not a factor in this design, and tell me why the reference that you are trying to use to disprove me states EXACTLY what I keep saying.

I keep stating something which is proven by your quoted reference, and yet you keep telling me it's wrong. That doesn't make sense.

davesrose wrote in post #3662651
Even though the inventor himself calls the green one "luminance-sensitive elements".

You should spend less time thinking about what the inventor of the filter thought it might do in the 70's, and spend more time thinking about the way the camera and your computer processes the image data in 2007.

Perhaps we should also use statements made by Henry Ford to characterize modern automobiles?

bill boehme wrote in post #3662850
I agree with many of the things that you have stated, however, the dynamic range is not a function of whether the recorded image is stored in 12 or 8 bits. The lower number of bits only means that the ability to distinguish between levels of luminosity will be diminished. We can define black and white levels for an eight-bit image in software to be the same as we would be for a twelve-bit image ... it's just that the eight bit image would not be able to distinguish between various levels most especially towards the dark end of luminosity.

Excellent.

Yes, I have. It is a very interesting development, as they are clearly giving up color information in exchange for more sensitive luminosity information. I suspect that the end goal for this is purely noise-related, but I would be very interested to see what the result is in terms of images. I wonder to what degree the reduction in color information will be detectable.

bill boehme wrote in post #3662927
I believe that you might be taking the statement too literally ... it is true that most of the luminance in visible light is in the green part of the spectrum because that is where our visual acuity peaks. However, the data is not processed as a L*a*b* model so the only place where it is actually treated as luminosity data would be for B/W conversions as your quoted source says.

The modified Bayer filter that I alluded to in my previous post does use actual luminosity data from high sensitivity panchromatic (clear) sensors to produce its L*a*b* output.

Bravo. I am happy to know someone else understands.

kpt4321 wrote in post #3674357
You should spend less time thinking about what the inventor of the filter thought it might do in the 70's, and spend more time thinking about the way the camera and your computer processes the image data in 2007.

Still, the point was that you refused to believe the inventor used the terms "luminance" for the green channel/ photo sensor vs "chroma" for red/blue. Believe it or not, lots of color spaces are from even before the 70s. And since the Bayer sensor is still in use with most cameras.....it seems to be very much in the now And for the umptenth time....the green channel is called the luminance element because it's got the most definition in luminosity, and therefore can generally be considered the luminosity channel in RAW.....as many systems will also just read the green for quick contrast data.

And since I work with 16bpc and 32bpc images, I think I do know a thing or two about 2007 image formats....I for one realize that I get more levels on a 12bpc RAW and that's why it's better with PP then 8bpc

The point is that image data gets converted to color spaces: additive and subtractive color have many differences in hue and value. With light, most information is luminosity and not chroma...color hues are completely different for additive and subtractive color systems...you have different values for sRGB, aRGB. HSB, HSL, Lab, CMYK, etc.

kpt4321 wrote in post #3674357
Please, tell me again that the human eye was not a factor in this design, and tell me why the reference that you are trying to use to disprove me states EXACTLY what I keep saying.

I never said "that the human eye was not a factor in this design": I just said it's not the only reason why there's extra green elements: As an optical component is different then the final processed image. You are the one who has said that there is no such thing as a luminance element or channel: funny you even said that after I linked and quoted the wiki article: it specifically says that green is luminance-sensitive elements, blue and red chroma-sensitive elements right after the line that you like to quote about the sensor being similar to the human eye.

kpt4321 wrote in post #3674357
I keep stating something which is proven by your quoted reference, and yet you keep telling me it's wrong. That doesn't make sense.

You asked me why the green elements were called luminance elements originally. I told you....and then you told me I was wrong and went on about the human eye. I have repeatedly said I realize that Bayer chose green to fill the extra space to be more like the human eye, but that since there's extra green photosensors, that's why they're considered luminance elements. And when the image gets processed, it is not going to have the same processed hues as what the sensor recorded. You were the one flaming me about something that even the inventor coined

kpt4321 wrote in post #3674357
It is a very interesting development, as they are clearly giving up color information in exchange for more sensitive luminosity information. I suspect that the end goal for this is purely noise-related, but I would be very interested to see what the result is in terms of images.

I'll give you a hint: luminosity Color information is chroma and luminosity, with luminosity being the most significant. Having another photosensor just for luminosity is not giving up color information

Here's my two penneth.

From personal experience, my 1d2 has much better dynamic range than my 20D. Many times I've taken shots in strong light (all RAW) where the 1D2 has captured great detail in both the highlights and the shadows, whereas the 20D will not capture the same detail at both ends. You can have nice highlight detail and jet black suits or nicely detailed suits and blown highlights with the 20D, but not both ends together. For this reason I consider the 20D's 'practical' DR much inferior to the 1D2's, and not reliable for pro work.