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Scanning monochrome film in RGB and Grayscale: Which is better?
Most of us scan monochrome film using the grayscale option in our scanner software. What this does in most budget scanners is average the inputs from the red, green and blue channels. But most scanners perform significantly better in one channel than the others. Blue is often noisy, and red is often soft. So could we get better scans by scanning in RGB mode and then selecting the best channel to convert into grayscale? Well, I decided to find out. Here is a tiny (about 1/4" wide) portion of a 6x6 negative scanned at 1600 dpi on an Epson 1640 SU scanner. It was shot using a Planar 80/2.8 on a Rollei SL66 and in the original negative the eyelashes are very sharp. On the right, you can see the image scanned first as a grayscale, and then the seperate red, green and blue channels of the same image scanned as RGB. I used the channel mixer to create these in 16-bit mode. Conclusion? The red channel is much softer than the green or blue channels. The green channel and blue channel are very similar, but the green channel is the sharpest by a nose. In other words, a clear sharpness gain by scanning monochrome images as RGB and then discarding everthing but the green channel. Whoda thought? To make your own comparison more easily, click on each image to bring it up in a separate browser window, then arrange these so you can see the images side by side.
		1. Above: The image scanned using the 'grayscale' option in Vuescan

		2. Above: The red channel from an RGB scan of the same negative. This is clearly softer than the image scanned as a grayscale.

		3. Above: The green channel from an RGB scan of the negative. This is clearly sharper than the red channel, and also sharper than the image scanned as a grayscale. Check the ends of the eyelashes on the bottom right of the image.

Note: the RGB channels were separated out in the raw scan. They were then individually inverted. Black and white points were set to 0% clipping in all of the images. No USM was applied.
		4. The blue channel from the RGB scan. This is a fraction less sharp than the green channel, but clearly sharper than the red channel.

		5. The RGB scan converted to a grayscale. This appears to be identical to the image scanned as a grayscale.

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