From AI to HDR - Gamma & 48 vs 16 bit

All about SilverFast HDR and HiRepp (48bit HDR processing)

DSchulman
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Scanner: Microtek M1 Pro
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From AI to HDR - Gamma & 48 vs 16 bit

Postby DSchulman » Wed Jan 05, 2011 8:03 am

Hi, I scanned a lot of negatives and wonder if I need to rescan everything?

I use the Microtek M1 and scanned with Silverfast 6.6 on a Mac with Snow Leopard. I scanned the negatives for HDR in Silverfast Ai Studio but in the General Options settings I chose a gamma of 2.2 and checked the "output for HDR". My research on forums seem to say I should have not checked this if converting the negatives in HDR and unchecked the gamma would be 1. I, also, embedded a 2.2 grayscale profile to each negative. When simply previewing each TIFF negative they look great with all the original negative info at least viewable on the computer screen.

So now in HDR which I upgraded to HDR 6.6, I am trying to correct for my attaching the 2.2 gamma to my negative scans. When I view them as positive they are quite dark. In the general settings, I marked "Gamma-Gradation" as 2.2. I even went up to 3.0 which seemed to brightened the image in preview. Then I check for HDR output which I guess I don't need check or do I?

Then with "Gamma expected in 48Bit/HDR", am I suppose to match my original scans gamma which was 2.2? It is all a little confusing because of variables.

Finally, I scanned the negatives as 16Bit HDR Grayscale, but it seems that in the HDR program that outputting to 48Bit Color provides more tonal information and outputting to 16Bit Grayscale. Which should I use to maximise data in original 16Bit HDR negative.

One last note, I intend to do final processing in Lightroom. So any help with these questions would be appreciated as soon as possible.

Thank you.

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LSI_Ketelhohn
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Re: From AI to HDR - Gamma & 48 vs 16 bit

Postby LSI_Ketelhohn » Thu Jan 06, 2011 9:36 am

DSchulman wrote:Then with "Gamma expected in 48Bit/HDR", am I suppose to match my original scans gamma which was 2.2?

Yes that is correct.
You should set the expected gamma to 2.2 if that was used for scanning the HDR files.

DSchulman wrote:Finally, I scanned the negatives as 16Bit HDR Grayscale, but it seems that in the HDR program that outputting to 48Bit Color provides more tonal information and outputting to 16Bit Grayscale. Which should I use to maximise data in original 16Bit HDR negative.

Separating the 16bit HDR file into three color channels does not provide more image information.
But you should use the file format best suited for your workflow.
Many Photoshop filters will give different results on a RGB image than a B/W image.

kind regards,
Arne Ketelhohn.


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