Vivitek H1180HD projector test: where the gamma curve takes you?

TEST LIKBEZ OVERVIEW: Gamma Curve

Which picture is bright! I can confirm that nothing in the house compares to the image of Vivitek H1180HD projector: neither old CRT-person, nor LCD-panel, nor “plasma” – all this didn’t stand beside… Maybe it’s all emotions, because everyday greyness and not very lively colors are everywhere – even on the parade of LED-panels in hypermarkets of electronics. But today emotions aside, we will “check the harmony” with the help of algebra..”Check the projection picture with measurements, graphs and charts.

The author of the test: Alexei SOROKIN.

Test Measurement Methodology

The Vivitek H1180HD projector was tested in complete darkness, as the projected image is much more influenced by ambient light than monitors.

The projector was placed two meters away from the Sony View Screen. The zoom is set to maximum. The final image size was 115×70 cm 0.8 sq. m. .

Measured with X-Rite i1Display Pro colorimeter, 30 cm from screen. Free software HCFR Colorimeter 3 was chosen as the software.1.0.6. Since the developers of the program are not concerned about the financial side, this program understands the correction profiles supplied by the colorimeter manufacturer.

Spectral correction profiles are intended to increase the accuracy of measurements – due to the corrections to the measurement results, which were made depending on the type of backlight of the displaying device CRT, CCFL, W-LED, Wide Gamut, Projector and others . In our case, the only choice is the profile designed to measure projectors.

Six main projector modes were selected for testing: Movie, TV, Presentation, Game, sRBG and Bright. We were interested in the main parameters that affect the image quality:

• Contrast
• Gamma curve
• Grayscale
• Color rendering accuracy
• Color gamut
• Color temperature stability

All conclusions are in one table

In the summary table you can see the main data about the image quality produced by the Vivitek H1180HD projector. All the results of test measurements are divided into two blocks – lightness and chromaticity, it is from these two elements add up any color in the usual sense of the word.

		Film	TV	Presentation	Game	sRGB	Bright
Lightness	Contrast	280:1	247:1	430:1	257:1	166:1	1528:1
Average Gamma	2,34	2,33	2,15	2,33	2,12	1,82
Average dE grayscale	12,43	17,21	20,95	20,75	13,32	10,48
Color	dE R	30,20	35,20	46,30	37,00	10,20	61,10
dE G	45,90	47,40	59,20	48,80	26,90	49,20
dE B	21,50	17,70	25,40	17,80	16,60	48,20
dE Y	15,00	11,90	17,20	14,30	9,70	14,00
dE C	36,30	45,20	47,10	43,00	37,60	25,40
dE M	27,60	31,30	39,10	32,90	20,50	46,50
Average dE of primary and secondary colors	29,41	31,44	39,06	32,31	20,26	40,74

*dE is defined by the CIE76(ab formula the parameter dE is the delta between some reference value and the obtained result .

Recall that the “contrast” parameter is the ratio between black and white point of the formed image. It may seem that the values given here are extremely low and blatantly fall short of what they are supposed to be.

However, today’s test shows everything within the bounds of decency. Because we are talking about real contrast without any additional marketing tricks like dynamic contrast, which can reach unimaginable 10 000:1.

In reality, if you put next to two monitors with the same image but with different contrast ratio of 1000:1 and 500:1, approximately one viewer out of ten will notice the difference.

To clearly see the difference between the two “contrast” parameters, you need to display a black or white image, depending on how that very difference was formed – from shifting the black point or the white point.

How gamma correction works in the projector

For clearer and more precise understanding of the role of gamma curve parameter in any projection device we refer those who wish to take an extensive course in digital image processing – click here.

The projector modes studied are clearly divided into four groups:

1. sRGB – low contrast, low enough to be clearly visible in visual evaluation. Gamma is very close to the reference 2.2, but slightly too high, the image will look more “flat”. But the probability of “shadow failures”, when the dark areas become a black spot, is significantly reduced.

2. Film, TV, Game – quite low contrast, although quite acceptable for a projector. In the contrast area, no visual difference between these modes is visually noticeable. Gamma is significantly lowered, the image will be darker.

3. Presentation – the mode has almost twice the contrast compared to the previous group. Contrast is increased by shifting the white point. In this mode, the gamma is closest to the reference 2.2.

4. Bright – extremely high brightness. Gamma in this mode is not overestimated, it is probably deliberately set to 1.8. Indeed the image looks very bright, but visually it looks more like a G=1 ratio.0 and G=1.8. The image is flat, unnatural, and very strange in terms of colors, but more on that later.

Understatement of gamma in some modes is reasonable enough, because the projector will not always be exploited in the dark. Ambient light will increase the overall illumination, and reduce the contrast of the image. Visually it would be comparable to gamma reduction. Nevertheless, the reduced gamma in movie mode is quite strange, because movies are usually watched in darkness or dim light.

Color fidelity

How accurately the projector can render colors, this obviously affects the quality of the image. But to what extent?

As we have already noted, the accuracy of color reproduction is determined by the dE value – the difference between the obtained result and the adopted reference. To illustrate, I will give you an example with a picture showing two red colors. The visual difference between them is described by the value dE=14.

On the whole, the dE parameter is high for almost all modes, which, however, is quite expected for a projector.

Looking at the average dE for primary and secondary colors, as well as in the case with contrast and gamma, it is obvious to divide all modes into several groups:

1. sRGB – the lowest value, we can say that for the projector is a very good indicator, which is achievable not for all monitors, especially installed in laptops.

2. Movie, TV, game – dE about 30 – visually the difference to sRGB is noticeable, but not annoying and not striking.

3. Bright, presentation – the highest dE values. In the case of presentation mode the difference is not so noticeable, however, in bright mode, taking into account its gamut, the image looks terrible.

Grayscale

Now let’s move on to a deeper analysis of the image produced by the projector. Below are the RGB Levels charts for each mode. The horizontal axis describes the change in brightness from black to white, the vertical axis at the top is the percentage, and the bottom is the dE value.

Ideally, the pink line describing dE should be minimal it is this line that is used to get the average value of dE of grayscale in the table.

Primary color lines should run at 100 percent, a deviation means that a point that should be neutral will get some tint, or be lighter or darker than it should.

Note that except for the Vivid mode, the green channel is perfect and goes exactly to 100 percent. Blue values are too high in all modes, especially in Presentation and Game modes. These two modes are almost never switched off in the charts below. The closest to the reference values are Film and sRGB modes. Essentially from all other modes stands out Bright – overgrown content of green, and most importantly undergrown content of red.

We will see the effect of these deviations when we look at the color gamut and grayscale wedge of each mode, but for now, let’s look at the Luminance curves for each channel.

Color shades and picture quality

Now we are going to get into the most interesting curves, which illustrate the values of each of the three main colors. Whereas the RGB Levels chart was just about grayscale, now it’s about the image as a whole.

The key to understanding the graph is simple: the tighter all three color curves are pressed against the reference gamma-grid 2.2, the more natural and realistic the colors on the screen will be.

Any deviation of any curve, red, blue or green, will mean that a particular color will lose some of its hue and be somewhat paler than colors with the correct curves.

As in all previous cases, Film, TV and Game modes do not differ much from each other. The difference lies in the channel ratio, but in the end the overall gamma curve is almost identical. Presentation mode has a weak S-curve, which is familiar to those who are engaged in photo processing.

The general rule is: the steeper the curve, the higher the contrast. By making the curve steeper in one area, the other inevitably becomes flatter. The S-curve enhances the contrast of the midtones, although in our case it is slightly shifted to the light area.

This is a very interesting and appropriate solution for the Presentation mode, since this is where most of the information on the slides falls. The high contrast of this area of gray tones will help keep the slide readable even in bright light.

In sRGB mode the curves of the channels match each other, it is very good, sometimes even more important than matching the reference curve. Bright mode stands out as always.

Channel curves run well above the reference – this is understandable, since the reference is 2.2, and the measured gamma value, recall 1.82. It’s worth noting that in Presentation and especially Bright mode the curves change. For example, in Bright mode, the red curve is higher in dark tones and vice versa in light tones. This will mean that the color balance will be somewhat unstable with changes in image brightness.

Color Coverage

Let’s proceed to the last series of measurements, which will objectively evaluate another important parameter for image quality – color gamut. To help you better understand the results and make an informed evaluation of Vivitek H1180HD projector let me give you a little background information.

As long ago as the 1930s they managed, with the help of mathematical transformations, to accurately enough simulate the visual color space – CIE-diagram, “the colored horseshoe”, which illustrates the whole range of colors perceived by the human eye..

In 90’s sRGB standard was developed, a kind of color standards: it gives a reference point of what purity should be the primary colors and what shades are achievable when mixing them, as well as the standard defines the white point. On the CIE-diagram, the sRGB standard looks like a triangle with the coordinates of the primary colors in its vertices.

The projector color gamut will also be represented as a triangle on the CIE-diagram: it shows how much of all colors available to our eyes can be reproduced by the projector. Everything is very clear.

The main question: how well does the color gamut cover the “horseshoe” CIE-diagram and how cool it looks against the sRGB triangle? Now we are ready to answer the key questions.

In addition to the color gamma, the charts below also show the color temperature and the grayscale for the different modes.

The primary colors are located along the edges of the CIE diagram, and as you approach the center, they blend to form a white point. In order to estimate the color gamut of the projector, a triangle is plotted on the CIE-diagram, the vertices of which are the measured primary colors output by the projector. Triangle area – all colors projected. The sRGB color space is shown for comparison.

The black line describes the positions of the standard color temperatures. The generally accepted color temperature is 6500K, the color temperature of daylight. If it’s bigger the image will be cooler, if it’s smaller the image will be warmer.

The color temperature of the device is determined by the gray wedge. Grayscale wedge – black and white gradient points marked on the CIE coordinates. The point of concentration of dots in relation to the black line is the color temperature of the projector. If the dots are off to the side of the curve, that means that there is a stray color tint in the image.

Overall color gamut is very good for a projector. In Presentation mode, the blue point is noticeably shifted relative to other modes, which narrows the color gamut considerably. Vivid mode gives the best description of reds and blues, but the worst description of greens.

The gray wedge points have little variation, except for the darkest value, which is perfectly normal. This means that the color temperature is stable through all gray levels. The bright mode has the closest to the reference 6500K color temperature, but the points are considerably displaced relative to the curve, which means a very strong greenish-yellow tint, which spoils the whole picture.

Film and sRGB modes have almost the same color temperature of 9400K, but Film tends to have a slight pink undertone and sRGB to green, with a generally more consistent color temperature.

Exactly here we see the difference between the Film, TV and Game modes – the color temperature, which increases in the same sequence. Presentation mode is almost identical to Game mode in terms of color temperature.

Why are the values so prone to cold? The answer is quite simple. Most light sources used indoors have a warm color temperature. They will compensate for such cold values of the projector. It is not practical to make specific measurements, even if you have lamps with the same color temperature as in our laboratory you will see a different picture. Because of the difference in light levels, the color of the walls from which the light is already reflected with the shade of these walls, etc.d.

Summary: A good entry level cinema projector

On the whole, the Vivitek H1180HD cinema projector can be positively characterized. It provides a sufficiently large color gamut, decent elaboration of the light and shadows, with the exception of the Bright mode, in its rays there are no parasitic shades.

The range of the modes corresponds to its name. Movie, TV and Game modes have medium contrast and low gamma. This makes the image more saturated and “contrast”, a cooler color temperature, which in conditions where the accuracy of color rendition is not required, is a plus.

It is not for nothing that when we want a white shirt, we add blue instead of green or manganese. We’re used to white being bluish to us. True white at 6500K will seem a bit yellowish to many people.

Presentation mode will be useful for the same use. An underestimated color gamut in this case does not play a special role, but the S curve gamut and enhanced contrast will definitely improve the readability of a slide even in bright ambient light.

The sRGB mode will be useful when color accuracy is important, as it provides the lowest dE. Gamma close to the reference also allows you to get an image close to the reference. The low contrast of course is a bit of a letdown, but you can live with it in comparison to the advantages.

As for Vivid mode, as it stands, I can’t find a sensible use for it. The image is too flat, with strong parasitic tint and dE in colors. And high contrast is like a spoon of honey in a barrel of tar.

If we don’t speak in terms of charts and graphs – let’s put it simply – the Vivitek H1180HD projector gives you a color picture more than 30 thousand Dollars. Want to watch good movies on the big screen in good quality – feel free to buy this model. But don’t try to squeeze Hi End out of it – a good-quality foreign car will never become an executive class car with a gold-plated steering wheel..

SCAN TEST LIBBYSE REVIEW: Gamma Curve