Can you view a HDR without tone mapping?

Discussion in 'Graphics Programs and Photo Gallery' started by prodigy2k7, Sep 3, 2008.

  1. prodigy2k7

    prodigy2k7 No longer a newbie, moving up!

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    How do you, if its even possible, view a HDR without tone mapping? How many stops can our eyes even see? How many stops can a LCD produce? How many stops can a print show? (Basically the range of stops)
     
  2. Moglex

    Moglex TPF Noob!

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    If the HDR actually represents a high dynamic range then you cannot see it on any normal output device - at least not to show the whole range represented in the file at once - without tone mapping.

    A lot!

    It does vary though, as we can't see them all at once. Our irises make fast adaptations that handle a considerable range but there are slower adaptations of the retinal components that can increase that range still further at the low luminosity end of the range.

    The dynamic ratio is around 20 stops.

    The static ratio (i.e. what you can see without making any adjustments) us around 6. This implies that you cannot see the full range of a decent LCD at once.

    Provided your monitor has 8 bit tables you can ascertain this for yourself by placing adjacent areas of a colour black against a pixel value of 1 in the appropriate channel and adjacent areas with pixel values of 254 and 255. you will not be able to see both differences at once.

    Generally six or eight per channel.

    That depends on how bright a light you shine on it, how reflective the white is and how non reflective the black is.

    Generally less that an LCD, though.
     
    Last edited: Sep 3, 2008
  3. terri

    terri Administrator Staff Member Supporting Member

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    I've moved this thread to the Graphics Programs forum due to its technical nature. We'd prefer seeing these types of discussions take place here.

    Thanks!
     
  4. Bifurcator

    Bifurcator TPF Noob!

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    you can't see all the different exposure levels at once but neither can you see the all the dark and light detail in a RAW image either so it's kind of the same deal.

    But yes, can load an HDR image into any of many of the editors that support it and view it. You can even save it with different default "view" levels.

    Here's a message from another thread that may apply:

    ==================================================================
    This is an EXR formatted HDR: http://tesselator.gpmod.com/Private_/PICT4482_PIZ_hdri.exr Load this into CS3 or another HDR editor (there are many) and select the exposure tool. Load it into Photomatrix and look ad the HDR histogram or use the exposure up/down tool in Photomatrix. ;)


    Had I saved it as a Radiance file it would have an .hdr file extension - as HDR is a file format. The difference between EXR and HDR is that the EXR format has more compression options, it's a little more robust (in terms of options), and it's an "open" file format meaning us developers can get twisted. :D See: www.OpenEXR.org



    -----------------------
    Here's a screen capture while looking at the HDR. Notice the exposure slider at the bottom of the window. ;)

    The first one is tone-mapped (a little extreme but not too different from what many people do.).

    The second one is a camera JPG.

    The third one is a true HDRI.
    [​IMG]
    ==================================================================
     
    Last edited: Sep 3, 2008
  5. prodigy2k7

    prodigy2k7 No longer a newbie, moving up!

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    thanks for input :)
     
  6. Helen B

    Helen B TPF Noob!

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    From measurements I have made on my prints, it varies from about 5 to 6 stops for prints made on matte inkjet paper, 6 to 7 stops for prints made on traditional light-sensitive glossy photo paper (up to 8 for glazed/ferrotyped B&W silver gelatin) and 6 to 9 stops for prints made on glossy inkjet paper. That is the range of the image itself, and it is independent of the amount of light falling on the print, but it does depend on the directionality of the lighting. The dynamic range that the eye has to deal with is lower because the eye does suffer from flare, which reduces contrast. You also need quite good lighting to see shadow detail in a print with 8 or 9 stops of density range.

    The variation in range is mainly because of the change in reflectivity of the darker areas of the print.

    You can compare this to sunlit scenes with deep shade - in that case your eyes may be scanning over a scene with a 13-stop brightness range, and your perception is that your eyes can handle it, even though they are not coping with the entire range at one instant. 13 to 14 stops appears to be about the largest range we can appear to see 'at once' (albeit not truly instantaneously).

    From observation and measurement, I'd estimate the eye's overall dynamic range, allowing for adaptation, to be at least 27 stops and maybe a little more.

    Best,
    Helen
     
    Last edited: Sep 3, 2008
  7. prodigy2k7

    prodigy2k7 No longer a newbie, moving up!

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    Thanks :)
     
  8. Jim Benton

    Jim Benton TPF Noob!

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    Thanks Moglex, Bi and Helen.

    I tried the test suggested using paint and creating custom colours and found that only with the greatest difficulty could I detect differences of 1 in the colour values. I got other people to look (including children in case it was age related) and everyone found the same. No one could detect whether or not there were blocks with the smallest possible change (using green) when looking at a whole screen that was half 255/254 and half 0/1.

    Not a very scientific test but interesting all the same.

    I also tried checking the range of glossy inkjet prints from unprinted to solid black but could not measure a range greater than 6 stops no matter how the light was angled.

    I'd love to have some tips for increasing that as it would surely make a lot of photographs a great deal more dramatic.
     
  9. Helen B

    Helen B TPF Noob!

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    Good lighting for a print will allow you to get viewing conditions close to the density range that would be measured by a densitometer*, while poor lighting will reduce the apparent density range. This generally means that the print needs to be lit at 45 degrees to the viewing axis with little light arriving from anywhere near to the viewing axis, so that there are no specular reflections. In general I find that the greater the density range of a glossy print, the more important is the lighting. Matte prints, though they have a lower measured density range, appear to be more able to hold up in poor lighting because the high density is less reliant on lighting angle - the blacks are velvety.

    A 6-stop density range is at the low end of what can be expected from a glossy inkjet print. What paper and ink/printer were you using, and how were you measuring the range?

    Edit: Doing a 0/1 - 254/255 test is quite demanding on the monitor and monitor profile - the contrast between 0 and 1, and 254 and 255 is not a fixed value and it is affected by the monitor contrast range and the monitor profile. An alternative method for the simultaneous contrast test might be to start with pairs of values that are discernible when they are the sole values displayed, then make the test screen with the two pairs to see if they are simultaneously discernible. If anyone wants a test file with all 256 values arranged so that value x can be compared to values 1, 2, 3 and 4 away (and which can, of course, be cropped to show a limited range or set of ranges) I will try to make it available on here, or email it.

    Best,
    Helen

    *Typically a reflection densitometer reads at exactly 45 degrees to the axis of illumination - either the illumination is in a ring at 45 degrees to the measurement cell which is at right angles to the print - the typical Macbeth (sic) arrangement - or vice-versa.
     
    Last edited: Sep 4, 2008
  10. joecap

    joecap TPF Noob!

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    This is amazing.
    Note that all we have to do is "scan the scene with our eyes" and they automatically adjust to see what we are looking at.
    We don't even have to think about it. If we look at the bright sunlit part, our pupils (aperature) automatically adjust to see it in proper exposure.
    Then when we gaze at the deep shadows, we magically see the detail.

    Our eyes are amazing contraptions...says a lot about the God who designed them.
     

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