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Slide "Scanning" with a Digital Camera

by Roger N. Clark

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The camera you use to "scan" slides must output raw.

Set up your slide copy stand.

Use a blank slide (overexposed so clear transmission) and set up a custom white balance. Record an image of the blank slide.

On (most?) Canon cameras, here is the custom white balance procedure. Select custom white balance from the menu. Select the image you recorded above. If the image above was the last image you recorded, when you select the custom white balance from the menu, it will show the image. Select it by pushing the set button (button in the center of the wheel on the back of the camera). Next on the top of the camera LCD, select the white balance as the custom icon (see your manual).

Check lens at various f/ratios to get maximum sharpness.

I use Canon 5D Mark II 21 megapixel camera with a Canon 180 mm f/3.5 macro lens at f/8. Reproduction ratio is about 1:1.1 so I am sure to get the entire slide. Maximum sharpness for my setup is f/8.

Put a slide in the setup and make an image. Record raw.

Load dcraw on your computer for file conversion (dcraw is free). Convert with linear output in dcraw (example image name is IMG_2462.CR2): Note, you must do this on a command line.

dcraw -6 -w -g 1 1 -T IMG_2462.CR2

The -6 makes 16-bits/channel, -w uses the in-camera (the custom) white balance, the -g 1 1 makes a linear transfer function, and the -T writes tif output. The default output is sRGB color space. See the dcraw man page for other options if desired.

In photoshop:

1) Crop the image

2) Use the healing brush on dust spots

3) Convert to sRGB (even if already sRGB, as the sRGB definition from dcraw appears very strange on some computers).

4) Do other editing as necessary (e.g. if exposure of off).

5) I save over the tiff (if I need to re-crop, I can always convert from the raw).

6) Convert to 8-bits/channel and save full resolution jpeg

7) Resize as desired, sharpen and save as a new file name if you want some smaller image for faster viewing, or, for example, to send in email.

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First Published February 18, 2012
Last updated February 18, 2012.