NVidia cards and color shift

[Lauri Kettunen]

This post is just to share the experience how I managed to get rid of the color shift when changing between playback and scrubbing on the timeline in Premiere Pro 2.0. In case of nVidia graphic cards the ProspectHD readme file explains how the NVidia graphics cards shoud be configured to prevent color shifts between RGB and YUV conversion.

The new NVidia cards, such as GeForce 7600GS enables one to set a color profile for video overlay to control the colors. At first, when I tried this, the colors of the desktop also changed as if the system used twice the color profile. But now, amazingly enough, once I closed the NVidia panel, the colors returned to what they should be. Then, when I opened the panel again the system said the color profile is activated for the video overlay. And indeed, the color shift in the PPro 2.0 timeline disappeared when changing between playback and scrubbing.

Summing up, I suspect there is some software problem with the nVidia driver or with the color profile file created by Spyder2Pro, but nevertheless, eventually the graphic card works as expected. The colors during playback, scrubbing or those of an exported frame in Photoshop are so close to each other that I'm not able observe any differences.

[Graham Hickling]

So are you saying you used Syder2Pro to general a profile for the main display AND then a 2nd profile for the overlay as well?

I never thought of trying that - cool!

[Lauri Kettunen]

Originally Posted by Graham Hickling

So are you saying you used Spyder2Pro to general a profile for the main display AND then a 2nd profile for the overlay as well?

Let me put it in other words:
i) I first created an ordinary color profile for the monitor, Samsung SyncMaster 244T, using Spyder2Pro
ii) Then I set the generated profile as the default profile for the monitor
iii) Next I opened color correction from the NVidia panel and chose "video overlay"
iv) Under video overlay I imported the color profile generated by Spyder2Pro

Thereafter, the blueish magenta color shift when changing between playback and scrubbing on the timeline of a ProspectHD project in Premiere Pro 2.0 disappeared.

[Bill Ravens]

i'm sorry to disagree, Lauri, but this method will result in applying your color correction profile twice. The effect is especially noticeable in the luminance of the screen.

[Lauri Kettunen]

Originally Posted by Bill Ravens

i'm sorry to disagree, Lauri, but this method will result in applying your color correction profile twice. The effect is especially noticeable in the luminance of the screen.

Hmm, it's a pity it's not possible to demostrate over the web what happens.

Let's put it this way: Without the color profile correction the display is tinted towards blueish magenta. For example, if I open any grayish winter image in Photoshop, one immediately notices the unnatural tone in the snow.

When I set the color profile file created by Spyder2Pro in Windows Control Panel -> Settings -> Advanced -> Color Management, the blueish magenta tint in Photoshop disappears, but in playback of ProspectHD avi files in the timeline of Premiere Pro 2.0 the tint is still there. One can't avoid noticing it.

Now, in Windows Control Panel -> Settings -> Advanced -> GeForce 7600 GS there is a Color Correction tab. The Cineform ProspectHD Readme file gives instructions how the parameters should be set to minimize the color shift. Changing settings Brigthness, Contrast, Gamma, and under Video overlay settings Hue, Saturation one can adjust the video overlay without changing the colors of the desktop. This helped, but the result was not completely satisfactory.

The interesting thing is, there is a tab called "Apply color correction" and one may choose between

Desktop,
Overlay and
All.

The panel allows to import different color profile files to desktop and video overlay. What I've chosen is:

Apply color correction: Desktop, color profile: Standard
Apply color correction: Video overlay, color profile: Samsung SyncMaster244T (which is the file created by Spyder2Pro.)

So, Bill, you see the GeForce 7600 GS allows me to choose different color corrections for desktop and overlay. This is the first graphics card I've seen which (gives the impression it?) allows one to do such a thing. And, if nothing else, once I did this, the color tint in Premiere disappeared immediately. Grayish winter scenes appear now grayish without any change in colors between scrubbing and playback.

Still, all this is indeed puzzling. I wish they made the manual clear enough removing all the guessing needed to understand what the heck is going on.

[Graham Hickling]

Thanks for the extra info.

So ..... the "standard" profile you applied to the desktop - that's an Nvidia thing, or perhaps even an XP thing? But not something you generated with your Spyder, right?

[Lauri Kettunen]

Bill, I think now that you are right in suspecting there is something odd. If I've got it right, the hardware should not (yet) support adjusting RGB channels independently.

To check this, I made a clone of the system and updated the latest NVidia dirvers from the web. In the updated version I'm no longer able to set the color profile separately to desktop and video overlay. This seems to suggest there is a kind of lucky coincidence which causes the color shift to disappear. --Sorry for the confusion. Computers and software systems are rather confusing and easily lead to misconclusions.

[Bill Ravens]

I'm running an Nvidia Gforce 7800GT with the same desktop controls you have. I also use a Gretag Macbeth Eye One Display to calibrate the screen. One thing is certain, the way Nvidia manages color profiles is ...well, funky. Ati has a much more reasonable color profile management system on their video cards. But, all is not lost with Nvidia. I was able to gain some measure of control over the management of ICC screen profiles generated by my Eye One by downloading and installing Microsoft's ICC management tool, called WinColorSetup.exe. Without it, Nvidia desktop didn't give me a way of appropriately applying the screen color profile.

The way Adobe manages image colors within their applications is somewhat different than most others. They take control of the color mapping. So, if you're importing or exporting images from your NLE to Photoshop, you need to be able to manage these color management differences. For example, exporting an image from your NLE to Photoshop. NLE's manage color according to the RGB standard defined by NTSC in the USA. When you export an image, it's color mapping is RGB, by default. When you import into Photoshop, Adobe applies color mapping according to some user selected preferences. If you haven't selected sRGB, your imported image colors will be remapped according to the wrong color map. You need to look at EDIT/COLOR SETTINGS dropdown in CS2 to see what color mapping Photoshop is using. If you're applying AdobeRGB in CS2, it will distort the colors you see. Likewise, when you export the image back to your NLE, be sure you have the image set to RGB color map before you export it. Adobe will "tag" the image data withthe color map. If it's not RGB, your NLE will automatically use the RGB color map, and again, your colors will be distorted.

Hope this helps.

BIll R