4 Replies Latest reply on Mar 20, 2013 1:17 PM by John Danek

    64bit HDR scans histogram mostly on left half. ofcourse HDR is dark! Means less data??

    IdamIndia Level 1

      Hi,

       

      I am confused, and unable to understand why the HDR histogram is crouching to the left. Can someone please help?

       

      I got used to hearing that HDR scans will show dark. All sites and forums say "it is normal".

      Well, a dark picture has most of the histogram to the left, we all know that. Right?

       

      Now, if HDR is supposed to have such a histogram, it means the data is not distributed but rather "crunched" towards the dark left side.

      I am unable to belive this. But then, if I open such an image in Photoshop instead of Silverfast HDR, it looks the same.

      Amazingly the histogram says: 0-255. For 16bit images, shoudl this not be much larger than 255, 2^16? If I assume this, then the histogram shows only in a qaurter of the range.

      Is this GOOD news or BAD news? Or news as usual (get used to the bad news)?

       

      Referece: Image in Silverfast HDR:

      half histogram.png

      This above view is a phenomenon with all HDRscans, not a particular image specifc issue.

      Desparate for answers  Thanks.

        • 1. Re: 64bit HDR scans histogram mostly on left half. ofcourse HDR is dark! Means less data??
          gator soup Level 4

          what/how are you scanning (is it on the dark side)

           

          you may need to need to make an adjustment before you scan to get it closer to what you want (or make the adjustment you want in Photoshop afterwards)

           

          i would recommend doing both, get the scan close and finish in Ps

           

          u may be able to answer your own 255, 2^16? by moving an 8bit image in Ps> Image> Mode> 16 bits/channel and looking at where ever you are getting that info from to compare

           

          sorry, i am probably not much help, but i am not sure what your are talking about...

          • 2. Re: 64bit HDR scans histogram mostly on left half. ofcourse HDR is dark! Means less data??
            IdamIndia Level 1

            Ok, let me try to put my questions in another manner:

             

            First, HDRScans done in Silverfast8 produce 64bit HDR Tiffs - does two scans of the same image with differnet exposures to create HDR, 64bit = 16R+16G+16B+16infrared (for SW removal of scratch and dust)

             

            I have two questions essentially:

            1. 16 bit channel should have 2^16 range of shades/tones/values. While SW mentions range 0-255 (2^8). Well, in CS6 the histogram does not mention any such thing, it simply shows the histogram and Means, Median.... But the color Panel shows clearly 0-255.

            color range 256.png

            2. The world everywhere says HDR scan will be dark. And indeed the histogram has most data on left. If that is normal as is told, I am wondering why? If an image has more data (HDR!) than should it not be more distributed accross the histogram? With tone curve corrections, I can manage to pull the histogram in full range, but is that not something artificial?

             

            Hope this is clearer.

            • 3. Re: 64bit HDR scans histogram mostly on left half. ofcourse HDR is dark! Means less data??
              IdamIndia Level 1

              LSI (SilverFast guys) replied for my dark scans. Things I want to share:

               

              1. They admit the images are strangely dark, even though there is no clipping. They recommend to set "highlight point correctly", gamma is fine and more than 2.2 is not necessary. Also, that it may be due to images being dark (I wonder why so, as I enjoy them on my projector and differnet types of iamges, all look equally dark), or scanner lamp being dim or scanner driver not upto date. I will post as I investigate further

              here is how the thimbnails of various types of iamges appear

              VLT Thumbnails.png

               

              2. 16bit vs 8bit. Here is what LSI said:

              "The Histogram shows 8 Bit values for better handling.

              The internal calculation uses the 16 bit data."

              This is good to know, I wonder if this is the case with Photoshop too. Can anyone confirm?

              • 4. Re: 64bit HDR scans histogram mostly on left half. ofcourse HDR is dark! Means less data??
                John Danek Level 4

                Have you calibrated your scanner?  BTW, what scanner are you using?  SilverScanHDR makes it possible for calibration ( I'm surprised LSI guys didn't recommend it ).  Why are you scanning 16-bit?  If you are getting dark scans consistently, you might have a weak light source.  A good scan will show data all of the way across a histogram, but this depends on the image being scanned.  Scanners may inherently scan a little on the heavy side ina default way of capturing more than enough data that can then be dealt with in Photoshop by an experienced user.