Most people are under the impression that it is better to adjust the brightness of an image by using the analog gain function of their scanning software rather than by adjusting the image's levels in an image editor. The following test was performed to see if these perceptions are true for Nikon Scan and the Coolscan 4000 scanner.

The methodology involves scanning the same slide twice in 14 bit mode and Adobe RGB color space using a Nikon Super Coolscan 4000. One scan is made using analog gain and one is made at the default settings. The scan made at the default settings then has it's white point adjusted in Photoshop until the overall image matches the analog gain image as closely as possible. The images are then resized (except for the "actual pixels" images), cropped, converted to 8 bit mode, converted to sRGB color space, and saved out as high quality (Q=90) jpgs in Photoshop to make them viewable on the web. This system is not perfect due to the compression of the images, the subjective adjustment of the white point, and other factors but I believe it accurately shows the effects of the different ICE settings.

Analog Gain = 0 Levels Adjusted in Photoshop

Analog Gain = +1 (Master)

These images are crops of a larger photo of Caye Caulker which was accidentally underexposed by ~1 stop. From examining the sky, the image where analog gain was used exhibits lower contrast and generally appears washed out.

Analog Gain = 0 Levels Adjusted in Photoshop

Analog Gain = +1 (Master)

This is an "actual pixels" crop from the same photo of Caye Caulker used above. The image where analog gain was used prominently exhibits exaggerated grain compared to the image where no analog gain was used.

Analog Gain = 0 Levels Adjusted in Photoshop

Analog Gain = +.75 (Master)

In this "actual pixels" crop of a larger photo of La Parroquia, shadow detail is noticeably higher in the image where analog gain is used, but noise is more apparent also.

Analog Gain = 0 Levels Adjusted in Photoshop

Analog Gain = +.75 (Master)

In this "actual pixels" crop of a larger photo of La Parroquia, we can see that analog gain tends to increase the saturation and posterization of the color saturated areas of the image (the dress) but not the other areas of the image. From examining the skin and the background, the noise level also appears higher in the image where analog gain was used. From examining the dark regions of the hair though, analog gain provides the benefit of greater shadow detail.

Analog Gain = 0 Levels Adjusted in Photoshop

Analog Gain = +2 (Master,R,G,&B) Levels Adjusted in Photoshop

These test images are an extreme case where the photo was accidentally underexposed by several stops. The methodology is a little different in this example because both scans have their levels adjusted in Photoshop. The scan where analog gain was used has it's white point and gamma adjusted to provide the most detail possible and the default scan has it's white point and gamma adjusted to match the analog gain scan as closely as possible.

While initial impressions may have the analog gain image to appear superior to the default scan image due to increased color saturation and better shadow detail (seen in the face), further inspection shows that much detail is loss in the saturated areas because the colors are posterized. These saturated areas of the image also stand out from the rest of the image in a way that does not appear natural. The colors in the image where no analog gain was used appear muted and suffer from a magenta cast but because the colors are consistent throughout the image, they can be easily corrected with adjustments in Photoshop while fixing the colors in the analog gain image is considerably more difficult.

CONCLUSION: While using analog gain results in greater shadow detail, it has the negative side effects of lower contrast (resulting in images that look washed out), exaggerated grain, increased noise, and posterized colors. Based on the images that I have worked with, I would recommend that this feature not be used for general scanning except in cases where shadow detail is the main concern. Best results are often found in scanning at 14 bit color depth and adjusting the levels in 16 bit mode in Photoshop. By not using analog gain, there will sometimes be less saturation in the color saturated areas of the image but this can be adjusted using the Hue/Saturation command in Photoshop without the negative side effect of posterization found in using analog gain.