not smooth gradients

[shacharoren79]

hi,

i have a problem where i create a BW gradient i don't see it smooth. as if every few shades of gray it "jumps" to the next one. which resulting many "stripes" of gray.

i use two monitors, my main one is an apple 30" cinema display which i'm having my problem with

and an old 6-7 years LG CRT (F900B) which i use for all the pallets and other stuff.

the funny thing is when i move my gradient window to the second (LG) monitor, i do see the gradient smooth.

i thought someone which own a 30" cinema display can explain.

tnx much

[degrub]

what bit depth are you driving each monitor in the OS driver ?
What are the hardware native bit depths of the two panels ?

[Ken Bennett]

Not to get overly technical, but this sort of thing is just a fact of life with older LCD monitors (and the 30 inch Apple display is rather elderly in digital terms.) It does not handle smooth gradients very well. Try looking at the file at 100% - that might help, but then it might not.

[shacharoren79]

after checking carefully, both monitors are 8 bits per channel 24bit. 16.7 million colors.

just to say again,

1. Apple 30" Cinema Display

2. LG 19" Flatron F900B

as for my GPU i'm running nVidia 560Ti and the color bit depth assigned for both is 32bit true color.

this settings show both on the win 7 monitor settings and the nVidia driver window.


that's odd, if they are both the same why do i see such a difference?

[Herb]

Disclosure: I know didly about this stuff. FWIW; Last week I made a gradient in Photoshop on my notebook that is calibrated with i1 Display Pro. Looked like a BW step gradient for a TV! Well; not quite that bad, but noticable bands through the entire range. My reaction was that I could re-do the calibration with 'LUT' selected rather than 'Matrix', but I just do this for fun and don't fuss about things as much as I used to.

Presumably you have a dual monitor setup (outside my knowledge). Are both calibrated? You could try a single monitor setup/calibration using the suspect monitor. Compare results from Matrix and LUT options.

The guru on this stuff was Ethan Hansen. He was seriously knowledgable and seriously helpful. Unfortunately, a lot of his wisdom was lost when the Rob Galbraith forums died. Have a read on the drycreekphoto site. Here is one page that may be relevant:

http://www.drycreekphoto.com/Learn/Calibration/monitor_gradient.htm

[Herb]

Actually..... robgalbraith went commercial (might as well have died).... some posts are still available; e.g.

http://www.prophotohome.com/forum/colour-management/39232-banding-fact-life-colorimeters.html

[Nigel Johnson]

I assume that you are calibrating each monitor and using a video card or cards that allow separate calibrations - if not all bets are off.

When calibrating the Flatron CRT I assume you use the monitor controls to adjust the RGB levels and also adjust contrast and brightness - the result of being able to adjust a CRT is that less extreme adjustments are typically needed in the 8-bits per channel video-card look-up table and hence the chance of visible posterisation is minimised.

When calibrating the LCD Cinema Display you are only able to change the brightness of the Cold Cathode Fluorescent Lamp (CCFL) backlight - consequently it is likely that more extreme adjustments are made in the look-up table resulting in posterisation and the steps in the grey gradient that you are seeing - you would probably see posterisation and steps in one or more RGB colour gradients if you tested it. This is a problem with all LCDs that use CCFL or white LED backlights and do not have internal high-bit look-up tables.

There are a number of ways of minimising the amount of adjustment needed in the 8-bit video cards and hence minimise the possibility of banding. Depending upon the calibration software being used you may not have the option of using all the techniques. Some of these will require you to also adjust the calibration of the Flatron if you wish to maintain a colour match, although given that you are only using it for palettes this may not be a problem:

• Firstly, you should choose to use native gamma for the Cinema Display. This means that the look-up table only needs to accommodate the small variations between the RGB responses (in order to maintain an accurate greyscale) rather than forcing them all to change, possibly by large amounts. In colour managed applications the system will use its higher bit-depth to manage the change of gamma rather than the 8-bit resolution of the video-card; the use of the higher-bit depth will minimise posterisation. In non-colour managed applications you will probably see either a lightening or darkening of the mid-tones.
  
  
• Secondly, you can choose to use a whitepoint that is closer to the native whitepoint of the Cinema Display - for example choose 6500 K rather than 5000 K. Again this will reduce the adjustment needed in the video-card. You would be best using the same whitepoint setting when calibrating the Flatron.
  
  
• Thirdly, you could choose to use the native whitepoint of the Cinema Display. Once again this will reduce the adjustment needed in the video-card. Whilst worth testing, this option may result in a slightly magenta or green colourcast making it difficult to produce good colour adjustments. Soft proofing in Photoshop with all corrections enabled would correct for the colourcast however the program interface elements would still show the cast making accurate adjustment difficult.

I hope that this is of some help and that it reduces your problems.

Regards
Nigel

[Nigel Johnson]

Disclosure: I know didly about this stuff. FWIW; Last week I made a gradient in Photoshop on my notebook that is calibrated with i1 Display Pro. Looked like a BW step gradient for a TV!

Please see my previous post. The use of native gamma is even more important on most laptops as the LCDs they use are less than 8-bits per channel (if I remember correctly only 6-bits) and hence are even more prone to posterisation and banding.

Regards
Nigel

[Herb]

The use of native gamma is even more important on most laptops as the LCDs they use are less than 8-bits per channel (if I remember correctly only 6-bits) and hence are even more prone to posterisation and banding.

Thanks Nigel. I wasn't aware of the 6-bit limitation. That's 64 maximum BW levels - not exactly 'fine'. Seems like i1Profiler software doesn't offer 'Native' for my laptop. Having checked again, there are no big steps on a gradient, just a load of minor lumpiness all through the range.

It's probably less of a problem than it might seem. I will still have infinitely better control than a 'professional photographer' who uses a 'professional lab' that provides color management via the 'tweak your monitor to match this 'ere test print' system. That appears to be the standard approach in the UK today. Ten years ago we seemed to be at the start of a new era. Le plus ca change....as Sarkosy would say.

Out of interest; the Color Eyes guys at Integrated Color have just announced that they are working on an update that can use the retail i1 Display instrument. Theirs has long been accepted as the best software...... should be interesting.