Scanning for HDR Software

flatbed scanners for Epson

BobF
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Scanning for HDR Software

Postby BobF » Tue Dec 28, 2010 2:02 pm

I'm looking to get some insight into scanning for using scanned image files in HDR software (e.g., Photomatix).

HDR software works best with linear data. Image files from a camera may be gamma corrected via a colour profile but that gamma correction is reversed out by the software before merging the files.

With film, there are more complexities. There is the tone curve of the film, the gamma curve of any scanner calibration profile used plus the gamma of any colour profile embedded subsequently.

In order to get a scan that's as close as possible to linear, my thought is to scan in 48 bit HDR color, embed the scanner ICC profile which was created with a gamma of 2.2 and make sure 'for HDR output' is checked in the Options>General tab with the gamma gradation set to 2.2. Based on my understanding, this will reverse out the 2.2 gamma correction of the scanner profile and give me linear data off the scanner (but still including the natural tone curve of the film).

Feedback appreciated.

Thanks.

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LSI_Ketelhohn
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Re: Scanning for HDR Software

Postby LSI_Ketelhohn » Wed Dec 29, 2010 11:17 am

Dear Bobf,

Not quite.

the "for HDR" referrs to our SilverFast HDR software which has nothing to do with tone mapped images often called HDR images today.
If you check the option your images will be saved with the set gamma of 2,2.

If you leave the option unchecked the 48bit HDR image will be saved with a gamma of 1,0.

kind regards,
Arne Ketelhohn.

BobF
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Re: Scanning for HDR Software

Postby BobF » Wed Dec 29, 2010 1:46 pm

OK, thanks.

It's been a while since I did any scanning. In the case of neg. film if I recall, the 48 bit colour option (i.e., RAW scan) doesn't back out the orange film mask nor does it invert the image to a positive. Or are the film profiles still available to be used even in the RAW scanning process?

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LSI_Ketelhohn
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Re: Scanning for HDR Software

Postby LSI_Ketelhohn » Wed Dec 29, 2010 3:04 pm

Dear Bobf,

yes that is correct.
If you want to scan negatives you would need to scan into normal 48bit files and set the gamma to 1,0 in the options.
This however does not embed the scanner profile and will render the image into the target workspace.
The rendering makes it necessary to set correct shadows and highlights so you do not lose any color data.

kind regards,
Arne Ketelhohn.


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