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Quicktip: Displaying the infrared channel in iSRD

November 14th, 2009 · No Comments · analogue photography, Digital Photography, HowTo, News, Processing, Quicktips, SilverFast, Tips and Tutorials

iSRD (or infrared Smart Removal of Defects) is a tool in SilverFast which allows users to remove scratches and dust particles from transparencies (slides or negatives).

This process is hardwarebased and uses an infrared lamp (included in some scanners) to create a map of dust particles and scratches on the film.

It is possible to see the infrared channel information (dust map) while using iSRD for an accurate adjustment of the parameters in the advance mode of this tool, or to create masks and layers to correct a specific area of the picture while leaving other parts unaffected (this is especially useful while applying infrared correction to Kodachromes).

There are basically three visualization buttons which show the uncorrected picture, the corrected picture and the picture with the imperfections marked (the last option is active by default in SilverFast) but none of them shows the infrared channel information. Those buttons can be used with the key combination “cmd+shift” (Mac) or “ctrl+shift” (Win) to display the infrared channel.

Displaying the infrared channel while having the picture with deffects marked

Press the button with the red markings located right below the navigator in iSRD dialogue

Deffects marking button

Deffects marking button

This will show the deffects on your film detected by the infrared channel (see next picture),

Red markings on the picture

Red markings on the picture

the markings are also affected by the settings of the tool,  these are the spots to be corrected by SilverFast using special algorithms.

If you click (and hold) on the preview window (yes, the big window with the image), you will see the uncorrected picture with all its deffects (as seen in the next picture)

Uncorrected picture

Uncorrected picture

Release the mouse button and you will see the red marks again

So far so good but where is the infrared channel?

press and hold the key combination “cmd+shift” (Mac) or “ctrl+shift” (Win) and click on the image, the infrared channel will be displayed with all detected deffects.

Infrared channel

Infrared channel

Note the infrared channel has different grey values for representing different types of deffects, there is even a faded ghost of the picture itself.

These gradations and picture ghosts make the correcting task difficult (easier than correcting on the rgb but still difficult). At this point different algorithms will be applied (But… back to the point).

Displaying the infrared channel while visualizing the picture corrected

To see how the corrected picture will look like, press the button to the left of the one you used to display the deffects.

Corrected picture button

Corrected picture button

Corrected picture

Corrected picture

Corrected picture

You can then use the same combination of keys and mouse to display the uncorrected picture (click on the preview window) and the infrared channel (“cmd+shift” + click (Mac) or “ctrl+shift” + click (Win)).

But… I want to see the corrections in the infrared channel!

In this case the infrared channel must be permanently active in the preview window.

To achieve this, press and hold the keys “cmd+shift” (Mac) or “ctrl+shift” (Win) and change any parameter in the tool (either the values of the correction sliders or the different view buttons). Keep the key combination pressed until the infrared channel is completely shown in the preview window, after that you can release the buttons or hold them pressed and click with the mouse on the preview window to see different combinations.

If you want to change any correction value and wish to have the infrared map always visible, then press again the key combination and make your corrections using the sliders.

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