Archive for July, 2016

July 1, 2016

VA v IPS monitors for photography

Once upon a time we had no real choice over the format of our monitors. The most common monitor type that filled the vacuum created by the disappearing cathode ray tube (CRT) was the Twisted Nematic (TN) liquid crystal display in thin, flat panels like we see today. The currently dominant panel types of TN, IPS and VA are all liquid crystal displays, which means the crystals can fluidly change orientation under the application of current. As in your common grey and black digital watch, the crystals can let light through or block it. The crystals in a monitor are not luminous by themselves in the way a CRT phosphor is, but in fact the light comes through the backlight, and the colour of the light comes from the filter placed over the crystal. The filter stage is a rather lossy and imperfect process; it prevents the panel being both as bright as we might like- not letting all the white backlight through- and it prevents the black being perfectly black- the backlight tends to leak through or around the crystal a little. These facts adversely affect monitor contrast, something useful in a scene lit by strong sunlight for example.

From the point of view of photography, we clearly lost something in the general transition from CRT to liquid crystal in terms of luminosity and contrast. Of course modern demands of high resolution text were becoming increasingly hard to meet with the CRT, and liquid crystal consumes about a quarter of the energy of the former. New computers began to come with the flat panels which were cheaper and took so much less space. We are where we are, and for the moment, that means that numerically, TN is far and away the most common panel type. VA is probably next, but mainly in televisions. IPS is common in more upmarket computer monitors.

The drawbacks of TN are fairly well know to a mass-market audience by now, and it is most likely the reader is viewing one right now. The colours change depending on the viewing angle. Viewing a part of the screen from an angle above, the screen may be paler and the more red. Viewed from an angle below, the screen may be darker and more green. Even viewing the screen from dead centre, both theses colours can be seen in different parts of the screen… when the colour sent to the screen is the same one all over. Viewed from the sides, contrast fades instead. I assume the reader is already aware of this and needs no illustrations.

Various alignments of crystals have been tried. Twisted Nematic (TN) was literally a crystal that twisted in proportion to the voltage applied, in order to block the backlight. Different colours came from filters overlaid on the crystals.

The most well known alternative LCD to TN is IPS (in-plane switching), where the crystals lie along the plane of the screen. In contradistinction to TN, IPS blocks the backlight in its passive state with the backlight off. IPS has very good viewing angles all around for colour, with the colours remaining the same at very steep angles unlike with TN. However the basic vibrancy of the IPS panel is somewhat poor for technological reasons such as extra electronics blocking some backlight, and the crystals themselves letting some bleed through. Black depth is a problem, and contrast tends to stay around 1000:1, the same as cheapest TN.  Below is a photo of an IPS in action with a dark greyscale:ips-grey-test-straight In addition, typically IPS monitors from a slight angle around perhaps 20 degrees off-axis, allow the backlight to peep through, causing the legendary “IPS glow”. The screen background below is not black, but dark grey, yet the IPS sheen has rendered it rather milky and uneven, notwithstanding any evenness of illumination in the monitor itself:


This glow recedes again on steeper angles off-axis, to be replaced with mere lower contrast. But having predictable colour performance is at least a boon to photographers.

The third crystal alignment type, vertical alignment or VA, has the crystals aligned pointing perpendicularly to the plane of the screen so that the backlight is much less visible. VA ensures high contrast, typically 3x that of IPS, but as you can imagine from viewing something narrow head-on, the image changes significantly off head-on angles. Near a similar angle to that which you could see IPS glow, the contrast of VA lessens to merely an IPS level, but unlike IPS and more like TN, at greater than that angle the colour trueness begins to go, with the image taking on a slightly green and grainy low-contrast appearance. The first photo of the pair below is the relatively well-behaved IPS example; at this angle this display looks just dimmer than when viewed dead-on. The second is from a VA (specifically AMVA) monitor. The image is fairly bright but the contrast has very much washed out and the colour balance gone yellow-green. The streaks appear to be caused by moiré exacerbated by the filter over the VA screen.


If you sit fairly close to VA, on a dark background you can appreciate a spot closest to you that appears darker than the rest of the screen, a sort of “inverse reflection” that makes me think of a vampire shadow. This is visible at a slightly lower angle than the IPS glow. The near-black of the nearest left-hand side is in fact how the background does look in real life. But the far side, effectively viewed at a greater angle, has faded. Once again moiré mars the photo which is not evident in real life- my photos were extremely rough and ready.


This is the root of the VA so-called “black crush”, “contrast fade” or even “gamma shift”. The former term is the most common one, but rarely applies to modern VA monitors, because technically they can now display the continuum of the darkest greys towards black at the ideal angle. In this photo below, you should be able to see that all the dark squares are visible, yet they appear less distinct from each other the darker they are compared to the IPS photo :


Since there are more angles at which the ideal contrast fades, the latter term is now the more accurate.

Inherent contrast in a panel type can also make for wider gamut colour, as stronger colour filters can be applied, meaning any colour can be potentially deeper, more vibrant and more pure. It is as clear from the above as it is from looking at the panels, that with IPS the colour consistency from various angles is not a problem, but once you see something better, the lack of vibrancy is. So why doesn’t the lack of vibrancy of IPS get quoted more often? The reason may be that it is over a decade since LCD displays took over from CRTs in the consumer market and memories of high performing monitors have faded. A whole new generation that is so vocal on the internet just has no experience of professional CRTs. In their minds they are only comparing IPS to TN displays which are so problematic for photographers. The public is relatively ignorant of VA which is employed more commonly in televisions. VA is not even one of the most expensive types of display, so that TV manufacturers tend not to shout about the panel type itself. The public doesn’t realise it, but would probably be disappointed with the flat 1000:1 contrast of IPS displays for televisions even if the masses could afford it. Praise for television images tend to come more along the lines of “Rich and vibrant” than “True colour”. In fact photographers have long been used to shocking colour and overdone contrast on display televisions. Even my old television repairer used to tell me so!

I decided to write this short piece with quick and dirty illustrations because there are few practical examples of VA displays on the internet it has been pointed out only infrequently that IPS cannot be all things to all people. It regularly gets recommended as the only panel type suitable to photographers, which is not really true. The contest between IPS and VA is a relatively simple one: viewing angle colour consistency versus contrast vibrancy respectively. Everybody would like to think that they know what wrong colour is when they see it, but few give thought to a lack of contrast. So the question essentially is: how are you to know what you don’t know? Well, I’ll try to show you. I hope you have your monitor set up carefully:

amva-photo-crop-straight ips-photo-crop-straight

The images above are taken with a camera of dynamic range of well over the 3000:1 ratio necessary to represent VA- it seems that modern cameras are recording around 20,000:1 in ideal circumstances. But the first photo is of a fairly flat-lit scene on a VA monitor. The second is of the same scene on an IPS monitor. Both were near their sRGB calibrations and though not particularly close in colour- this IPS could not demonstrate quite all gradations in red and I matched for skin tones over white purity – the contrast had been calibrated carefully. Both monitors received very positive reviews by specialist sites and were priced similarly. I adjusted the photo to look correct on the VA monitor by comparing it to the original VA photo. So try playing with your contrast and brightness until the first VA image looks realistic to you- remembering that your perception has been conditioned by your own monitor- and then compare the IPS photograph, full-screen. [more test images to come, 01/07/2016]

If you can get past the difference in the green of this particular IPS, you may even on this flat scene receive the same disappointment that you get when stepping down from any high-contrast display technology down to IPS. Of course you can edit photos and in particular nail white balance  with less concern for viewing angle on IPS but this experiment hints that you need to take care with contrast. People are so used to expending effort on WB that they adjust contrast almost as an afterthought, yet it plays a crucial role in the perception of the image. Make no mistake about it, I know from experience it is tempting on an IPS to push up the contrast a little to give the image more ‘pop’ and find it simply too hard on a monitor with more realistic contrast. Please don’t do this and make those with better monitors suffer!

Knowing all that I do, could I recommend a VA monitor (in this case AMVA) for photo editing? The answer is a qualified yes, but it is better suited to watching videos. You need to understand what you will be getting. The ‘vampire shadow’ example photo of gamma shift shows that you need to keep a certain distance from the screen and fairly centralised to be able to experience the several times greater contrast benefits VA has to offer, without experiencing the weirdness. Unfortunately I only avoided the gamma effect when viewing at a distance of about twice the diagonal- most people look at monitors at a distance similar to 1x the diagonal of the screen. IPS on the other hand, is significantly less fussy. Though the sheen or glow from looking at IPS quite off-angle is a mild nuisance, it has nothing like the deleterious effect on judging photos that off-angle viewing of VA would… though you have to remember you would never be unaware you were in the wrong spot to view VA properly- it is quite obvious when you aren’t. Those shooting with their own controlled lighting will probably not miss the contrast of VA much. For those shooting in natural light, the contrast of VA is a significant advantage in appraising the images.

I have noted with the best modern cameras that some are using them at low iso with a maximum dynamic range which is way above that of typical display technologies, and the images look quite peculiarly flat in the lack of contrast when the photographer has tried to showcase all that fancy range they were conscious they were paying for. But also I have seen a fondness from amateurs for making photographs habitually just a little too hard and brassy and suspect they have been editing on old IPS whose contrast is even lower. Photographers should take care to calibrate their own brains for contrast as much as they do their monitors for colour!