Color banding appearing on screen of gray image?

[Brian K]

Here's something I just can't understand. I've started scanning B&W negs of nighttime scenes. The scans are 16 bit rgb but the end result is a gray scale image, desaturated and lacking any real color. However in the deep gradation of the night sky there appears to be a subtle green to magenta banding. It does not appear on any prints, even color prints, and does not register as having any color banding when checked with the eye dropper.

To make matters even more confusing, even when I convert the image from 16 bit RGB to 16 bit gray, or lab, or CMYK, the banding still appears on the screen. This banding appears on both my Eizo coloredge and iMac monitors. I'm assuming it's some sort of color space issue but again it appears as an sRGB, Adobe 1998 RGB and Grayscale gamma 2.2 color space.

[Preston]

Brian,

Are these monitors running off of the same video card? If so this could be a video card driver, the video card itself is running hot, or the card is failing. Try updating the driver to the latest one from the card's manufacturer and see if that helps. If it doesn't you'll have to dig deeper.

--P

[Adrian Pybus]

Your screen is calibrated wrongly?

[Brian K]

Thanks for the reply, the monitors are calibrated, they do use the same video card, but it's a new card..... did either of you see any weird color banding on the sample image?

[Kirk Gittings]

I didn't.

[Brian C. Miller]

+1 on video card and/or driver. Does this show up on your system when you view the image at 1:1 zoom or larger?

This doesn't show on either of my screens, but I've seen it before. When the greys are averaged, there's something in an algorithm that fudges on the colors, so you get the banding problem. Try updating your video drivers. If that doesn't work, then look into getting a different card. (Everybody always wants an excuse to upgrade their stuff, right?)

[Adrian Pybus]

Thanks for the reply, the monitors are calibrated, they do use the same video card, but it's a new card..... did either of you see any weird color banding on the sample image?

No, no colour banding on my monitor.

[Preston]

Brian K.,

No, I am not seeing any banding on the sample. Even if its a new video card, the supplied driver on the install CD may be an older version. I suggest you update to the very newest version just to see if the issue goes away.

You might also check the Enable Open GL Drawing Advanced Settings in Photoshop under Edit>Preferences>Performance to see if it is set properly for your system.

--P

[patrickjames]

What hardware/software are you using to profile your monitors Brian? It is definitely an issue there.

[Ken Lee]

Another vote for no banding. Just a simple iMac, but calibrated.

What operating system and what software are you viewing the images - a web browser ? Photoshop ?

If you view the image in a different viewer, do you still see it ?

Does the problem only appear in JPG files ? After all, JPG compression is not perfect. Do you see it when viewing the file in TIFF ? PSD ?

What happens when you convert the image to 8-bit ?

(Just trying to isolate the problem.)