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Choosing an LCD Monitor for Photo-Editing/Viewing

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Contents

Introduction
Three LCD Technologies
Screen Brightness
Graphics Cards and Power Supplies
Calibration
Color Bars
Some web sites discussing monitor calibration

Introduction

Choosing a computer monitor for viewing and editing photos has become quite difficult these days. CRT monitors are history, and the predominant choices now are LCDs. Compared to CRTs, the common LCD has higher contrast and higher saturation than CRTs. LCDs usually use a fluorescent back light. The problem with fluorescent lights is their spectral response is dominated by emission spikes at specific wavelengths, whereas sunlight is more continuous light at all visible wavelengths. The main problem with LCD panels is that contrast, brightness and color changes with viewing angle! Maintaining color, brightness and contrast is critical for accurate photo editing. Adding to these complications is the fact that there are currently 3 different technologies used to make LCD, and only the least common, most expensive technology (called S-IPS, described below) is good for photo editing. The most common LCD panels, including all/most current panels used in laptops, use the cheapest technology (call TN, described below) which suffers the most from changing brightness, contrast and color with viewing angle. LCD monitors also have higher edge sharpness than do CRT monitors, thus images that were "sharpened" when viewed on a CRT may look over sharpened when viewed on an LCD monitor. All these issues raise complications on how one edits photos for display on a web site where the predominant viewing public will be using low quality TN LCD displays with the contrast set too high and they may be viewing off the optimum angle and seeing the wrong colors.

In choosing an LCD monitor and looking at manufacturer specifications, keep in mind that there is no standard (that is adhered to) regarding what is the viewing angle, and of course, manufacturers generally do not tell you what their definition is, nor do they generally tell you which technology is used in the LCD panel. So different manufacturers may use different standards for viewing angle, nor do the viewing angle specifications say anything about contrast or color shifts. The viewing angle specification is generally how much light decreases off axis, and different manufacturers use different levels for this cutoff. The viewing angle is a horizontal specification, and ignore vertical problems, which are generally much larger! Because of these problems, choosing an computer monitor has never been more complicated.

Three LCD Technologies

S-IPS LCD Panels. IPS stands for In-Plane Switching. These are the highest quality (and generally most expensive) LCD panels made today. S-IPS panels have the largest color gamut, high color accuracy, and largest viewing angles. But the technology is slow, so this technology is generally avoided by people wanting to view fast action, as in gaming, or viewing movies. However, the speed gap is closing and newer S-IPS monitors tend to have faster response times. S-IPS panels are currently the best LCD technology for photo editing and viewing.
VA LCD Panels, S-PVA/MVA. VA stands for Vertical Alignment. VA panels have similar specifications to S-IPS panels but not quite as good. VA panels generally have higher contrast ratios (not necessarily good for photo editing) and better black levels. However, they suffer from color shifting with different viewing angles and thus should be avoided for photo editing and viewing. Currently, many 24-inch LCD monitors are S-PVA technology.
TN LCD Panels. TN stands for Twisted Nematic. These are the most common LCD panel type found, as they are cheap and offer fast response time for gaming (typically 2 to 5 milliseconds). TN panels are currently used in most/all laptops. Unfortunately, TN panels offer the worst color shift, contrast shift, and intensity changes with viewing angle. Laptop screens are typically opened to an approximate viewing angle, and the vertical viewing angle probably varies more than a typical desktop setup. But the vertical viewing angle color and contrast shifts can be extreme, even over a few degrees of angle. When viewing a uniform color on a laptop screen, the color appears to change from top to bottom of the screen at a single viewing angle! This makes consistent photo editing very difficult. As of this writing, most 22-inch LCD monitors are TN technology.

You can find additional information on LCD technologies here: www.pchardwarehelp.com LCD Panel Technology Explained.

The web site lists monitor specifications, including monitor type when known: www.widescreengamingforum.com Master Monitors List.

The Master Monitors List web site, as of this writing, lists only 5 S-IPS 20-inch models, and 5 S-IPS 30-inch models. The site does not list Apple Cinema displays which are reportedly all S-IPS technology. The Apple Cinema, Dell, and HP 30-inch monitors reportedly use the same S-IPS panel made by LG. Apple Cinema displays come in 20-inch, 23-inch, and 30-inch panels. Thus there are currently 13 known S-IPS LCD monitors on the market as of this writing.

Screen Brightness

I currently use a 30-inch 2560x1600 (4 megapixel) pixel S-IPS LCD monitor and it is my experience in using multiple monitors from various manufacturers (both S-IPS and other types) that the brightness and contrast is set too high from the manufacturer. Other LCD technologies are even worse. Thus ALL LCD monitors must be calibrated in my opinion. An important step before calibration is to turn down the brightness.

Here is a way to measure screen brightness and relate the result to what you see (we could measure in Lux units, but photographers generally do not have lux meters, but do have good light meters). Consider the sunny f/16 rule: exposure is 1/ISO at f/16 for an 18% gray card. For a white sheet of paper, about 5 times brighter, the exposure would be 5 times faster than the sunny f/16 rule. Remember, light meters try and make everything mid-level gray, not that this faster exposure would correctly make white paper white. I am making this example so other photographers can measure their monitors. If you make these measurements, use at least 10 sheets of paper stacked together, or thick photo paper. Changing the measurement to f/8, the sunny white paper measurement would be 1/(20*ISO) at f/8. At ISO 100, f/8 white paper would meter at 1/2000 second. This brightness level is generally too bright to view detail (white paper in full sunlight appears very bright to our eyes). Now measure your monitor on a completely white scene. You can make this in a photo editor, or many word processors start with a blank white screen. What measurement do you get? It should be a longer exposure than 1/2000 second at f/8. ISO 100. Table 1 shows some measured values under different conditions. The idea is to make you monitor brightness a level similar to how you view prints. For displayed prints, measure the exposure time on white paper placed where the print will be displayed. Adjust you monitor to a similar brightness.

Table 1: Metered Exposure time of White Paper or White on Monitor, ISO 100, f/8

Bright sun: 1/2000 second
Cloudy bright: 1/500 second.
Bright room light: 1/25 second.
My calibrated 30-inch S-IPS monitor: 1/13 second.

Graphics Cards and Power Supplies

Few graphics cards will drive a 30-inch 2546 x 1600 display, so before buying one, make sure your graphics card can handle it. The next issue is the graphics cards that drive 30-inch displays require a lot of power, so be sure your power supply can handle the card. If you plan on running dual monitors, be sure the card and power supply can handle the job. Also be aware that most (current) graphics cards can calibrate only one monitor, so you either have to buy two of the same monitor, or one monitor has the calibration of the other (which can result in strange colors).

LCD monitors should be run only at their native resolution. While you can use other resolutions, images, lines and text generally look worse due to the larger pixels, interpolation and pixelation effects.

Calibration

Unlike CRT monitors where many display images well using factory settings, all LCD monitors I have had experience with (dozens) have out of the box too high contrast, saturation, color cast and brightness. LCD monitors must be calibrated. There are multiple ways of doing this, from observing web sites with graphics designed to help calibrate, use of Adobe Gamma, to hardware that measures actual screen colors, brightness and contrast and then applies software to make corrections.

Setting the monitor's Color temperature is the next step in calibrating the monitor (after brightness, discussed above). The default color temperature of LCD monitors is usually (always?) set wrong for photo editing. First, a little information on color temperature.

Color temperature is the temperature of a body emitting heat (all bodies emit heat, even snow on a cold winter day), but in photography, it is the equivalent color temperature of a warm or hot subject emitting those colors. Consider an electric stove burner or heating element. As the temperature increases, you see a deep red, and as the temperature rises, the color changes to orange, and if really hot, it will turn whiter, as in a filament in an incandescent light bulb. But the light source does not have to be hot to produce color. For example, the blue sky is scattered sunlight, or you could put a blue filter in front of a light bulb. Color temperature is the equivalent temperature of a light source of a heated subject called a Black Body and is expressed on an absolute temperature scale in degrees Kelvin (Kelvin = Centigrade + 273). A color filter in front of a black body changes the measured color and thus the color temperature. The more blue the color means a higher color temperature.

Some color temperatures:

    Electric Stove Burner:    ~  1,000 K
    Candle Light:             ~  1,500 K
    Tungsten light:           ~  3,000 K
    Sunlight, sunrise/sunset: ~  3,200 K
    Camera Flash:             ~  5,500 K
    Sunlight, overhead:       ~  5,800 K
    Overcast Sky:             ~  7,000 K
    Blue Sky:                 ~ 10,000 K

The typical LCD monitor factory setting has the color temperature set around 9,300 K. The problem with this is white will have a blueish cast, and all colors will have a blueish cast. This will make images on the monitor different than if you print them, and the appearance on screen will not be what you saw when you took the picture. Prints are typically viewed in room light with color temperature much lower than 9,000 K, so you should set your monitor color temperature to something in the 5,000 to 6,500 K range. Some LCD monitors have specific color temperature settings.

After setting brightness and color temperature, you woukd ideally use a monitor calibration tool to fine tune the contrast and color balance. Here are a couple of links with more detailed help:

Dry Creek Photo, Monitor Calibration and Profiling. Current (2008) information.

Dry Creek Photo, Monitor calibrators reviewed. (check for newer devices than in this review.

Color Bars

Below are a series of gray-scale and color bars. They each range from 0 to 255 on an 8-bit scale, and are 256 pixels wide. Each bar should appear smooth with no banding (except the step bars) or color shifts. Shift your head left and right and up and down. There should be no changes in color or where black starts to appear. On the gray-scale step bar, you should be able to clearly see all 17 levels.

black to white.
black to red.
black to green.
black to blue.
black to cyan.
black to magenta.
black to yellow.
black to salmon.
green to red.
white to red.
white to green.
white to blue.
rainbow.
gray-scale steps.