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Re: Bob Newman Information Theory Article

Discussion in 'AP Magazine Feedback & Suggestions' started by Blind Pugh, Aug 10, 2016.

  1. Blind Pugh

    Blind Pugh Well-Known Member

    As usual, I always read Bob Newmans technical articles with great interest.
    After reading this week's article on information theory I arrived at the the conclusion that what Bob as explained is a similar principal to what most cameras use to produce out of camera jpegs that are well . For example fujifilm in camera DR settings protect highlights and then apply a curve to the shadows similar to the one shown in Bob's article.
    Have I understood the article correctly or am I missing the point ( as I very often do ! ).
    Cheers Ian.
     
  2. Learning

    Learning Ethelred the Ill-Named

    I do not know what most cameras do. I expose to the right. In high contrast subjects that results in shadows and even mid tones being dark. That was the case in his example; at first site it seemed underexposed but in fact was only just protecting information in the highlights (sky)'. I would hope that most cameras do as he suggested and automatically produce good jpegs. I am not convinced that they do. If you don't trust the camera then shoot raw + jpeg and inspect the histogram on a trial shot. Be prepared to use the raw record in high contrast situations.
     
  3. Terrywoodenpic

    Terrywoodenpic Well-Known Member

    If you shoot raw +jpeg and expose to protect the highlights, but just short of clipping them, then the jpegs are not going to be much use.
    The shadows and mid tones are going to need a lift in most situations. This is of course quite easy to do in curves from a raw file, but would certaily loose data using a jpeg.

    Today is seems to be something of a sin to let extreme highligts burn out, even in back lit shots. When the fact is it can be highly effective, and still have a fantastic tonality.
     
  4. Blind Pugh

    Blind Pugh Well-Known Member

    If only camera manufacturers would give us a live Raw RGB readout on the histogram.
    I mostly bracket my shots by 1stop either way when the situation allows this usually give me a chance to get anew exposure close to ideal.

    Cheers Ian.
     
  5. Terrywoodenpic

    Terrywoodenpic Well-Known Member

    sounds like a good idea, but it would need to be selectable or it would give the wrong information to jpeg users.
    I suspect it would take rather more time to produce, so would not be the default setting.
    A selected button press and hold to produce it overlaying the image, would be just fine... with blinkies at 5% inside the black and white points, which are usually the first and last visible tones.
     
  6. Learning

    Learning Ethelred the Ill-Named

    How much more time? The processing capabilities of the latest Nikons, and also presumably Canons and Pentaxes seems to be greater than a full blown PC of only a couple of years ago!
     
  7. Blind Pugh

    Blind Pugh Well-Known Member

    Surely this is possible.. my fujifilm x30 has an option to turn of the film simulations to give a flat / neutral jpeg rendition in the LCD with the standard luminance histogram. It would now be a step forward if we could have a live RGB histogram taken from the RAW output...is this so difficult to achieve ?.
    I use micro four thirds and also Sony SLT cameras, ideally suited to all of the above information implanted in the elecfronic viewfinder. This is the big advantage for me over optical dslr viewfinders...?real time information.

    Cheers Ian.
     
  8. Terrywoodenpic

    Terrywoodenpic Well-Known Member

    I suspect it will be possible some day, but you can never actually see a raw file as it is not a display file like jpeg or tiff. You would need to create a file from it that contained all the display information it contained in the form of a hdr. which be useless for looking at, but from which you could extract a histogram of the entire captured data. At the moment they create the histogram from the display jpeg contained within the rawfile.

    when you process a rawfile in lightroom or the like you are seeing the adobe file using the settings captured at the time and read from the exif data. You do not see the hidden data, until you adjust a slider. You never see all the data at once. If you move all sliders to their extreme you see a very flat compressed version that is within the gamut of your display, but not a true representation of the wide range captured.
     
    Roger Hicks and Blind Pugh like this.
  9. Blind Pugh

    Blind Pugh Well-Known Member

    Perhaps i should stick to bracketed exposures !!.
     
  10. AlexMonro

    AlexMonro Old Grand Part Deux

    There's no difficulty in creating a histogram directly from raw image data, either simple luminosity, or with just a little more work, RGB (you don't need to do full demosaicing for optimising the information content of the exposure). It's more straightforward than creating a histogram from a JPEG, since you don't need to do the decompression. It probably won't bear that much relation to how the scene looks to the eye, but that's not what you want for evaluating exposure. With a few tricks, such as using shifts and truncation to multiply and divide by powers of 2, and choosing appropriate scaling, it can probably be done quite quickly too.
     
  11. Terrywoodenpic

    Terrywoodenpic Well-Known Member

    If it is so easy why do we never see this done anywhere ? Not in camera nor in processing software.
     
  12. AlexMonro

    AlexMonro Old Grand Part Deux

    Well, several processing / raw conversion programs I use certainly can display raw histograms - UFraw, RawTherapee, AftershotPro (nee Bibble).

    As to why we don't see it in camera, it's probably to do with marketing / perceived demand / perceived user acceptance.
     
  13. Terrywoodenpic

    Terrywoodenpic Well-Known Member

    How do you know it is not calculated from the display view, rather than the raw.
     
  14. Blind Pugh

    Blind Pugh Well-Known Member

    I have used UFraw, Raw Therapee and Aftershot Pro I had no idea that they display the Raw data. Aftershot Pro as a Raw development program is a complete Joke ( in my humble opinion ) .
    With Mirrorless cameras it seems like a logical progression.... that is my logic though!.
     
  15. AlexMonro

    AlexMonro Old Grand Part Deux

    Well, IIRC, they give you the option of looking at input and output histograms. The output histogram of course reflects the output image, which is usually the display image (give or take the monitor gamut). When I've got time, I'll dig through the source code of UFraw again and show you if you like. The wonders of Open Source! :)

    Of course, in a sense, the distinction between display view and raw is more nebulous in a raw converter - the display goes through demosaicing and the basic curves to create the colour, but doesn't have all the other stuff associated with JPEG. A histogram that can show the RGB channels has got to do basically the same processing.
     

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