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kelvinproblem
kelvinproblem
Participating Frequently
April 28, 2020
Question

32 bit HDR levels

  • April 28, 2020
  • 2 replies
  • 1415 views

Hello, 

I've got a set of 7 exposures that I am using merge to HDR on, but every time I do it they dont show the full range of dark tones.  So, I tried to use the levels adjustment as I ordinarily would on the 32 bit radiance file and it does not work.  It shows a total full histogram as though it were an ordinary file.  Now, I slide the hdr slider at the bottom and can see much more info, but I still want to set the black point in a ways.  No clue how to do this and I've been looking for hours.  Kinda new to 32 bit and all but I've done photoshop for over 20 years.  Thanks for any suggestions.  Just want to set black point and white point in 32 bit HDR file.  

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2 replies

davescm
Community Expert
davescmCommunity Expert
Community Expert
April 29, 2020

A 32 bit file works differently to an 8 bit or 16 bit file. 

In 8 bit or 16 bits the levels between black and white are split up into 256 steps (or 65536 steps in 16 bit).  Both have the same level of black and the same level of white. You can of course adjust the black or white point within that range.

 

In a 32 bit image things work differently. No monitors are capable of displaying a 32 bit image. There are levels in the image that are darker than the black on the screen and levels brighter than the brightest white on the screen. Moving the slider you refer to allows you to see those additional levels by adjusting which part of the full range is being shown on your screen. So you don't have a normal black point as such as the file can contain blacks darker than those on your screen.

When converting back to 16/8bit you choose how those levels are mapped onto the range that can be shown in 8 and 16 bit. You could for example just map the blackest point in your image to 16 bit 0 and the brightest to 16 bit 65536 and have it linear in between, but that would look extremely flat. So when you choose to convert back you will be given a choice of mapping methods and mapping controls which will allow you do adjust the way you want the image to display on a normal 16 bit image. That is the point at which you choose what levels in your image you will map to your 16 bit black point, and white point.

 

Dave

kelvinproblem
kelvinproblemAuthor
Participating Frequently
April 29, 2020

Hello Dave.  Thank you for your response.  I should say at the outset that I do not want to have 16 bit or 8 bit output.  I'm trying to make a 32bit HDRI for 3d modeling use primarily as a lighting source.  It is pretty imperative that it have a full range from 32bit black to 32 bit white.  And I see what you are saying about "16 bit 65536" but I don't know how to set this.  With levels?

Also, I realize that I am cheating a bit trying to fix black point and white point and then map this to a 32 bit full range of tones.  The fact is that despite shooting a bunch of pictures, they didn't produce a true 32 bit black.  I can tell because when I drag the 32b slider, it goes to black about 20% earlier than it should.  So, I will continue to experiment when shoorting to hit absolutely the full range out of the raw file.  But also this is the way that I have always made good exposure from the camera - shoot a bit flat and then set white point and black point in photoshop to confirm that I got all of the information and have not clipped detail.  I'm just trying to do this more or less in 32 bit. Can you advise me how to set that black point using any of the photoshop controls for 32 bit?  Thanks!

    Chuck Uebele
    Community Expert
    Chuck UebeleCommunity Expert
    Community Expert
    April 28, 2020

    Are you doing this in Photoshop or Camera Raw? Camera Raw has better controls.

    kelvinproblem
    kelvinproblemAuthor
    Participating Frequently
    April 29, 2020

    Hello.  I have tried in both to conform the tonal range in my 7 exposures to the full range.  I tried setting blacks and whites and exposure in Camera Raw.  And I have tried using levels in Photoshop proper to set black point and white point. If you have any guidance I would be happy to try in either software.

     

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