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.)

[jb7]

I see horizontal banding, but not in colour. Here, it looks like too much jpeg compression is emphasizing it...

[Brian K]

I'm using a MacPro 5.1, 8 cores, 32 gig RAM, ATI Radeon 5770 with 1 gig VRAM. The main monitor is an Eizo 21" ColorEdge CG 211. I have the graphics card also feeding my 27" iMac as a second monitor. OS is Snow leopard 10.6.7 (10.6.8 does not support proper calibration of the iMac when used as a second monitor). I have to use Snow Leopard because my scanner software, oxygen for the IQSmart, does not work with Lion.

The banding appears in the file at all sizes from 4400 ppi down to 950 pixels wide. 8 or 16 bit, rgb, grayscale, cmyk, Lab, does not matter. Tiff, PSD, PSB, or jpeg, does not matter. I'm wondering if the video card simply does not have the ability to support both monitors, but the problem still appears when just the Eizo is used.

[patrickjames]

What hardware/software are you using to profile the monitors?

I would recommend you dump the video LUTs (there is a free program called ProfileMenu that will allow you to do this easily http://www.macupdate.com/app/mac/26191/profilemenu ) then recalibrate and rebuild the profiles.

[Brian K]

Patrick the Eizo uses it's own proprietary calibration, and if I understand correctly it has it's own video card built in. As for the imac it's calibrated with a Gretag macbeth i1 photo UV cut.

[patrickjames]

I hate to help people out over the internet Brian, but I guess that is what we have. If you still have the problem I would recommend a couple of things. First, dump the dyld cache. You can do this through Terminal but I prefer to just clean the entire system at the same time with a program called Onyx which is free. I do this weekly. The dyld file clearing is under the Automate tab in Onyx. You will need to restart your computer afterwards. You should also do the video LUT clearing I mentioned above before the restart AND before you clear the dyld file. After restarting rebuild the calibration and profiles. I am assuming you are using Eye-One Match 3.6.3 with the Spectrophotometer. My guess is that these steps will fix your problem since the problem is spanning two monitors. Let me know if it doesn't and we can move forward from there.

[Brian K]

Well I tried the recommendations, and I appreciate all of those, and it hasn't seemed to really help. The problem is far more apparent on the iMac and much less so on the Eizo. I think what I will do next is buy a second video card and run each monitor individually on them.

[Peter Mounier]

I can see some banding. It is very subtle. If I move my cursor through the very ill defined edge of the red band the rgb values stay the same, but the cmyk values change by one percent in the yellow and magenta. When I move up to the green band. the rgb values remain the same but the cmyk values change in the opposite direction by 1%. I have very old Apple Studio display. It took me awhile to even see the what appears to be two bands, one red and one cyan, more or less going across the center of the image. Sorry, all I can do is verify that you're not imagining it.

Peter

[Peter Mounier]

I thought I'd try to find out if the banding that I see is a monitor or driver problem by creating a new document and filling it with gray. No banding there at all on my monitor with the test image.

Peter

[Lenny Eiger]

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, but I did see some circular white scratches.

;-)

Lenny

[Greg Miller]

...but the cmyk values change in the opposite direction by 1%...
Peter

That's just how CMYK behaves. That happens with RGB files, but also with grayscale files. Create a canvas in Photoshop, set to grayscale, fill it with black, then put a gradient on it so the tones range from black to white. The use the color checker to sscan over the values and you will see the CMYK values are not all equal to each other. Do the same thing but in RGB mode and you will see the RGB values all equal each other but the CMYK values do not.

[pbryld]

Nothing here either. 2009 iMac with all the cheap stuff. No upgrades. Never calibrated for anything.

[tnsporting90]

Depending on the current settings in the printer driver, you can make changes to the settings to improve print quality:
1. For the Colour/Greyscale setting, select Colour. For the Image Type setting, select Photo.
2. For the Media Type setting, if the setting is currently Plain Paper, change it to Inkjet Paper. If the setting is currently Inkjet Paper, change it to Brother Premium Glossy Photo Paper.
Thanks.