How to process RGBi files from scanner.

[keithdunlop]

I'm looking into doing some of my own scanning when I don't use RPL, and in researching scanners (specifically the Plustek 7600) which provide an infrared channel for dust and scratch removal.

I use Lightroom for post-processing. The way I understand it, Lightroom (and for that matter Photoshop) cannot see the extra channel and therefore all information beyond the red, green, and blue channels is discarded.

I don't understand the point of scanning with dust/scratch removal if you can't edit the file as you would any other file. How do you work around this?

 

[Arjay]

Use dedicated scanner software like Silverfast or Vuescan (or the software that came with the scanner) and activate ICE.

The ICE function uses the data of the fourth (IR) channel to eliminate dust and scratches. Disclaimer: This only works with color, slide and chromogenic BW films. Negative film that retains silver in the finished strips is unsuitable for ICE.

Said scanner programs will use the IR channel data, but only deliver a three-channel (RGB) file for subsequent processing. IR channel data will be discarded after they have served their purpose.

 

[Tim Gray]

Photoshop can see the IR channel. It's up to you to build up an action that can do something with it. I'm working on this as a PS action and as an automated routine with ImageMagick. Both basically process the IR channel to make it suitable as a channel mask for use with the healing brush.

 

[keithdunlop]

Said scanner programs will use the IR channel data, but only deliver a three-channel (RGB) file for subsequent processing. IR channel data will be discarded after they have served their purpose.

Really? Not according to this review of the Plustek 7600 using Silverfast software.

"Once you have scanned to Raw, however, your processing options are very limited because image editing software (like Photoshop) doesn't know what to do with the infrared channel of either the RGBI or HDRi file.

If you open the Raw TIFF in Photoshop, for example, the Channels display will only indicate the composite and red, green and blue channels. The infrared channel is discarded.

So if you do any image editing on the file and save it, you will lose the defect removal information."

If I lose the defect removal information, doesn't the scan I open in Lightroom still have the visible defects? The defect removal information is in a fourth channel that gets discarded once I try to edit the file in Lightroom/Photoshop, no? Am I missing something?

 

[Tim Gray]

If I lose the defect removal information, doesn't the scan I open in Lightroom still have the visible defects? The defect removal information is in a fourth channel that gets discarded once I try to edit the file in Lightroom/Photoshop, no? Am I missing something?

In the programs I've played with, if you do dust removal, the scanning program applies the fixes, deletes the I channel, and saves a 'fixed' RGB file. If you save it as a 'raw' file (RGBI or RGBA for alpha), there usually isn't any dust fixing going on in the RGB part of the file. The 4th channel, I for infrared or A for alpha contains a map of where the dust and scratches are.

However, the fourth I channel is NOT a layer/channel that has the 'fixed' image data. It's a grayscale image of just the dust and scratch location. I'd upload a sample but it really doesn't look like much. Silverfast and Vuescan can make use of these RGBI files to run their dustbusting routines after the fact. Or ou can develop photoshop actions to prep that channel to do something useful.