Author Topic: How does an incorrect picture look? (Warning: large images)  (Read 2745 times)

Offline KenMasters

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Hi, I came across this article on Flatpanels and thought I'd share with you guys. As you may or may not be aware, Flatpanels is a Danish site and although there is an english version ( www.flatpanelshd.com ), there is much content that has not been translated. I have asked permission and have translated the article for those who might find it interesting.

You can find the original article here: http://www.flatpanels.dk/***usartikel.php?subaction=showfull&id=1225350000 (It seems the swear filter is censoring the link, the missing three letters make up the not so nice afrikaans word for fornicate.)


How does an incorrect picture look?
By Torben Rasmussen

To get the most out of your display, it is important to ensure that the images it produces are as close to the creator's original intent as possible. Unfortunately most of the displays available today do not offer an optimal viewing experience, making it not only harder to decide on a display in-store but also impairing your viewing experience once you do get it home.

The fact that these displays are set up incorrectly in-store means that often consumers select one set over the other based on a false assessment of the panel's picture quality. Manufacturers purposefully employ various forms of visual trickery in order to one up the competition, typically through brightness, colour and sharpness manipulation.

In this article we will attempt to demonstrate how this manipulation of picture parameters impairs picture fidelity. It can often be very difficult to assess what is wrong with a picture, or indeed that there is even something wrong. We will start with a simple base image and proceed to manipulate it, in the same way manufacturers typically do, so that you might notice the negative effects for yourself. Since the entire purpose of these effects are to trick you into believing "the new effect looks better", we will include the original image alongside it as reference.

NB: For demonstration purposes the effects are a little exaggerated.

Original Image



This is the correct image of the three meerkats, the way in which the photographer wished for them to be depicted. Notice the colour detail, the highlights in their eyes and the texture of the bark behind them. We have also included a greyscale gradient on either side of the image in order to aid in demonstrating the affect of the various adjustments on the picture.

Overly Contrasted



In this example the contrast is too high, as is often the case with LCD TVs. This is a typical trick meant to catch our eye and separate one set from another. At first glance the image may appear more striking but this boost to contrast in fact obscures image detail. Look closer and you will notice how detail in both the light and dark areas of the image are lost. The effect is clearly observed when looking at the greyscale, quickly transitioning from solid white to solid black.

Boosted Colour



Again, a typical trick employed by manufacturers and retailers. Colours are boosted; adding extra red, green and blue; to create the illusion of deeper, more intense colour. Although this does not degrade image quality to the same degree as boosting contrast, it can still result in a loss of colour nuance, which can negatively impact overall detail. Critically for film, it can also alter the mood being conveyed, where the director might use colour to create a particular atmosphere.

Boosted colour is often notable on lips, which can appear sunburnt or even give off a slight red glow. Regardless of the degree to which the colours are manipulated, incorrect colour impairs image quality.

High Colour Temperature



A display's colour temperature, measured in Kelvin, is regularly manipulated in order to separate one panel from another in-store. When the colour temperature is set too high, the image a panel produces will be tinted blue and feel cold, stripping the image of it's natural look. In some cases it might even be pushed as high as 10 000 - 12 000 Kelvin, ridiculous considering 6500K is what we're actually looking for.

Low Colour Temperature



Rarely do displays have too low a colour temperature from the factory, but lower colour temperature options can usually be found within the settings menu, commonly labelled Warm. They may prove to offer a more accurate picture than the high preset, but can sometimes be a little too low. This results in an overly warm, sepia toned image, which can impart an olden day feel.

High Gamma



The correct luminance at each level of grey is important for proper image reproduction, as luminance is responsible for a great deal of picture information. In this image the gamma setting is too high, which results in the mid tones of the image appearing too dark. Note that the luminance of black and white are still correct and that the colours have not changed. It is only the luminance of the mid tones that are reproduced incorrectly.

Low Gamma



If the gamma is too low, the image will looked washed out and have no depth, robbing a film of its ability to draw you into a scene.

Poor Greyscale Tracking



Non-linear greyscale tracking is a very common problem with digital flat panels. Non-linearity results in colour errors within the greyscale. On our test image you can view these errors by means of the gradient, a red tint is noticeable towards the light end, green within the mid tones and blue towards the darker end of the scale. These errors are easy to pick up when viewing a greyscale gradient but quite difficult to identify when viewing regular material.

Overly Sharpened



One thing you often see in-store are sets with too much sharpness. Sharpness is a type of image filter all TVs come equipped with, and in some cases a little sharpening can be beneficial. Sharpness increases the contrast along the edges of objects in an image, giving the impression of a sharper image, but it is important to understand that this information does not come from the source material, it is simply an effect created by the sharpness filter. In the test picture you can clearly see the unnatural effect this has on the meerkat's fur as well as the line created along the edge where the image and gradient meet. This outline is the defining characteristic of over sharpening.

Posterization



If the internal image processing incorrectly breaks up colour gradations, posterization occurs. This appears as an abrupt break in an otherwise smooth transition of colour. This effect is most often noticed in scenes depicting blue skies or facial skin. In our example image the effect can be seen on the bark as well as the ground behind the meerkats and of course within gradients.

Poor De-Interlacing



An interlaced signal is a signal type that sends only half its horizontal picture information, in alternating lines, for each time your display updates. The frames are then stitched back together in a process called de-interlacing. When this process goes wrong, and the incorrect frames are stitched together, it results in jagged lines along the horizontal edges of an image.

Closing Remarks

As mentioned in the introduction, we have slightly exaggerated some of the examples in order to illustrate the discussed points more clearly. Out in the AV wild though, where these errors come in combination, it really becomes hard to figure out what's going wrong without measuring equipment. In the following image we have lessened the degree of exaggeration and combined a number of the above phenomena to create a more real world scenario. As you can see, in such a situation it becomes more difficult to put your finger on exactly what is in need of correction.


The following errors are visible in this image: Slightly high colour temperature, light S-curve to the gamma, slight sharpening and skewed colours.

 This image is far from unrealistic in terms of what you can expect from a modern display out of the box. We make use of measuring equipment and test patterns in order to accurately assess and correct errors. You can read about our findings and display settings within our reviews. However, if you want the most accurate image possible for your set, we would recommend you have your display calibrated in your viewing environment.

In closing we would like to add that it is a difficult task to calibrate a TV without the help of measuring equipment. Discs such as Digital Video Essentials and Disney's WOW can be a great help, but if you want as correct a picture as possible, it's hard to get around the need for calibration equipment.
« Last Edit: May 17, 2012, 09:10:23 AM by KenMasters »

Offline BWS

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Re: How does an incorrect picture look? (Warning: large images)
« Reply #1 on: May 17, 2012, 09:07:53 AM »
Thanks Ken,

This is a fab resource. While I haven't read it in its entirety, this is going to be valuable info.

 :clap:
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Offline naughty

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Re: How does an incorrect picture look? (Warning: large images)
« Reply #2 on: May 17, 2012, 09:17:30 AM »
terrific info  :clap:

Offline Stefan

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Re: How does an incorrect picture look? (Warning: large images)
« Reply #3 on: May 17, 2012, 09:22:25 AM »
Great stuff! Thanx!
(Insert inspirational quote)