Can't See Noise/Posterisation on Computer LCD Monitor

[HKdom]

Assuming my eyes are ok, I'm trying to edit my images using photoshop and be able see the point on screen where the image starts to break up from too much detail recovery / editing.

I am working off of an external LCD connected to my laptop (analogue connection). Sometimes when I edit a photo / graphics it looks solid on my external monitor but when I slide the image over to my laptop monitor (extended windows desktop) which is set at 1400 x 1050 also at 32 bit quality the image looks really posterised or noisy.

I can see "noise" on my external LCD monitor if I zoom in on my image 200% or more but posterisation is hard to detect even though it is very much there. The posterisation and noise even show up on another really old laptop set to 16bit colour quality.

My current specs are:

-Laptop graphics card ATI Mobility Radeon 7500
-Monitor resolution 1280 x 1024 at 32 colour quality.
-LCD Monitor SyncMaster 172T Colour calibrated using Optical Spyder

My questions are:

1) Why can’t I detect image noise and posterisation on my external LCD monitor but I can on my laptop LCD monitor? –Or almost anyone elses’ monitor for that matter.
2) Does resolution affect image quality i.e. would I see more details on a monitor set at 1600 x 1200 versus 1280 x 1024

[Scottes]

LCD monitors are very problematic with digital imaging. They lack contrast and are noted for color shifts at different viewing angles. Even the huge and wonderful Apple Cinema display isn't that great for digital imaging.

The fact that you're calibrating it is a very good thing, but are you calibrating all your monitors? If not that could explain some changes. In particular the contrast could be very different between the two - so you could have a change between contrast and colors shifts due to one being calibrated and the other isn't.

At the very least I would suggest calibrating the laptop if it isn't already. But moving to a CRT will most likely help your images, though it won't fix the differences between monitors. Calibration *should* but may not if the LCD monitors are too different.


Resolution of the monitor will not affect the image in any way. It will affect how you see the details in it, though. As resolutions increases pixels become smaller and thus look sharper. Smaller details, though, may be lost. You will get used to it though. Resolution will definitely not affect color, color perception, or the pixels themselves.

[Jesper]

Where the posterisation comes from:

Your laptop LCD monitor most likely cannot display 8 bits per color channel (many LCD monitors can't). So instead of 8 bits per channel, the monitor uses only 6 bits per channel. That limits the number of distinct colors the display can show.

A display that shows 8 bits per channel can display 8 bits x 3 channels (R, G, B) = 24 bits, 2^24 = 16,777,216 different colors.
A display that shows 6 bits per channel can display 6 bits x 3 channels (R, G, B) = 18 bits, 2^18 = 262,144 different colors.

So instead of 16 million, your laptop display can only display about a quarter of a million different colors, which leads to posterisation. You don't see it on your external LCD because it's probably a better screen that can display all the 16 million colors.

With "16bit colour quality", the display uses 5 bits for red, 6 bits for green and 5 bits for blue, which gives you 2^16 = 65,536 different colors - even less than 18 bits per color, so the posterisation will be even worse.

[HKdom]

Thanks for all that Scottes and Jesper, I appreciate your help! -I'll take the image I see on my external LCD at face value over my laptop LCD for now. I'm going to try calibrating my Laptop as well and since the resolution doesn't affect the image quality I wont worry about it :)

I gather LCD's are generally not good when it comes to image editing, but for example:

Would a regular CRT connected to my laptops' ATI Mobility Radeon 7500 be better or worse for image editing than a Syncmaster LCD connected via DVI to a Matrox Parhelia 128 card? -My laptop doesn't have DVI's only analogue inputs.

Sorry if that's a dumb question.

UPDATE: I profiled my laptop LCD using the Spyder and saved it but I cannot seem to use two separate profiles for each of the monitors. Under the windows XP properties menu I choose "settings" and then double click the #1 display and set the relevant profile. When I select the #2 Display and set that relevant profile and go back to my #1 display it changes to the #2 profile.