Philips BDP3000 Blu-ray Player Comments

I'm quite sure I must be asking a stupid question here, but some googling hasn't helped much so here goes.

Clearly DVD and Blu-Ray picture information is digitally encoded on the respective disk. My understanding is that HDMI is a digital cable/protocol so my assumption has been that the unmolested data stream is taken from the disk and handed to the display for rendering.

When you run tests like those described in this excellent review, and discuss picture quality, are you referring to the analogue outputs because if you are using HDMI I am struggling to see how the player could affect picture quality any more than the build quality of my computer's DVD drive affects the data that is read off the disks inserted.

I seem to remember from the early days of CD there are timing issues to be concerned about, jitter and so forth, but fundamentally no-one worries that a PC DVD or Blu-Ray drive would read bad data because of this so it is hard to see how it affects Blu-Ray/HDMI?

It's obvious I must be missing something as in my world there would be no picture quality difference between the cheapest supermarket special and the best Pioneer player but, analogue output aside, I just can't see it.

Appreciate any clarification (or links).

Cheers

Crash

Unlike CD audio, DVDs and Blu-Ray are compressed formats. The HDMI signal itself is de-compressed so it is the job of the player to process the compressed data stream and convert it to a de-compressed stream. How well it does this will have significant impact on the picture and audio quality.

Iain, thank you for taking the time to reply.

Having done a little reading around, DVD are compressed using MPEG2 and Blu-Ray with MPEG2, H.264/MPEG-4 AVC and VC-1 algorithms. In each case there is a great deal of discretion on how to compress a full HD picture using parameters to these functions, but as far as I can see there is no discretion on decompression. It is a mathematically precise operation that the player either can do or it can't, with no effect on picture quality. It seems analogous to unzipping a zip file on a PC. Either you can or you can't, a better PC will not unzip better data.

I'm still hoping someone will point out the error in my view. Has Trusted Reviews done any reviewer blind comparative tests of blu-ray players over HDMI to confirm these differences?

Kind regards

Crash

@Crash Biker...

My understanding is that the various players actually perform the decompression AND the rendering of each frame into their own video buffer.

The contents of the video buffer are then transferred to the display via HDMI/Component/DVI/VGA etc.

Different players have different characteristics in how well they perform the rendering, resulting in variations in 'qualities' such as fluidity of motion, smoothness of diagonals, handling/introduction/suppression of interference patterns (e.g. moire), and other details such as how well they render colour, contrast, etc.

A DVD/BlueRay player is not just a box that extracts/decompresses digital streams and squirts them to the display & sound system - it's more akin to a simple PC in that it introduces processing, RAM and a video card (well usually just a chip).

I'm sure others will add their own definitions and explanations, but hope this helps to being to explain why output quality really can vary so much.

Bailey's_Coffee

Thank you also for taking the time to reply. I'm concerned I'm going to look ungrateful and argumentative if I'm not careful so I'll intend this to be my last comment on the matter.

I accept that what you are saying is consistent with all the review comments, but what do you mean by "how they perform the rendering"? Taking your description at face value, and using the little knowledge I have of video equipment, the frame buffer is a digital page in memory. When the data is decompressed from the disc and the resulting picture says to set shade 001 of red in the top left pixel then that memory location is assigned that value. There is no variation possible. Now - you also mention Component and that is an analogue output and I fully understand that on some players Red 001 will be converted to 0.92 volts and on some 0.93 volts, and in a contrast change going from white to black then good players will drop from (making this up) 1.0volt to 0.0volts in 1 pixel whereas cheaper analogue to digital converters will slide through 0.5volts and blur the edge a fraction. When the frame buffer has to be scaled from 1920x1080 to 720x480 perhaps some do linear resampling and some do bicubic resampling and get a better shrink. I understand that the display has to do frame rate conversion and field interpolation and so on and the quality of the phosphor/plasma chamber/lcd pixel affects the contrast and colour shades.

But for a Blu-Ray player reading a blu-ray disk, decompressing the MPEGG4 to a digital data stream and passing that stream onto the display via HDMI I can see no ability to influence the picture quality at all. I accept there may be build quality differences, aesthetic qualities, extra features, load speed issues etc between an expensive player and a cheap one, but as long as it is connected to a full res display over HDMI and an equivalent amplifier with a digital data stream I cannot see how you would get a better quality picture from one over the other. Could we have a case of "The Emperor's New Clothes?"

Ah well, statistically speaking no doubt it's a racing certainty that I'm the confused one here so I will try and flaunt my ignorance no further.

Appreciate the effort.

Kind regards

Crash

@Crash Biker... I actually think your comments flag an opportunity here for a really interesting 'Trusted Reviews Special Article' - it's not at all obvious why playback variations should exist in a purely digital system - yet they do.

The difference between players is quite marked (even with DVD players - let alone decks that can handle the growing number of HD media types).

In the short term - something you can do by yourself is head to a decent A/V shop and ask to see two BlueRay decks from each end of the performance spectrum connected to the *same* 1080P display - so you can perform your own 'like for like' comparison on the *same* pieces of footage (be prepared to run slow-mo and freeze-frame tests to really see the differences up close - look particularly at finely detailed textures, diagonal edges on sharply contrasting areas of the image and fast moving objects).

You may be surprised at the differences - despite both decks being fed the exact same digital stream.

A lot of the variation is of course down to 'processing' of the raw data by the deck... most decks don't just output the flat/pure pixel data - instead they perform additional enhancement / filtering / dynamic-range adjustment / etc, etc - whether you want it or not!

The whole process of compression / decompression can result in 'artefacts' - which are basically areas of an image where the bit-rate of the (lossy) compressed stream is too low to represent the image details very well (ever seen a JPEG image that was compressed a little too much? It's the same principle at work here). Many decks use clever techniques to try to compensate for these difficiencies in the stream - with varying degrees of success (as do the majority of decent LCD / Plasma panels).

Whether or not you like the result of this additional processing from the deck or the display is very much down to personal preference (my wife really reacts quite badly to the 100Hz / 200Hz modes - finding them unnatural and uncomfortable to watch - yet other people love the extra fluidity).

The A/V market is full of manufacturers who want to differentiate their products from their competition - this is probably the most important piece of the jigsaw when it comes to understanding the variability of performance in the land of digital entertainment.

Hope you're still awake after all that!

All the best,


AlcoholicCoffeeRules!

@Crash Biker:
"In each case there is a great deal of discretion on how to compress a full HD picture using parameters to these functions, but as far as I can see there is no discretion on decompression."

As far as I understand, there is 'discretion' on decompression. It's the same as JPEG decompression: the skill of programmers still make a difference between decompression speed and image quality. Basically with (lossy) compression and decompression you get a set of rules to comply with. It's how you interpret and use the rules that makes the difference. This is more apparent with lossy than lossless compression.

Also, after decompression, players will post-process the image to remove e.g. compression artefacts. Again, here you get an added image difference between various players. This happens as well on your computer (GPU + videocodec + video playback software), and there are differences there as well. E.g. nVidia and ATi both have their own "video enhancing software" (PureVideo, Avivo Video).

On the hardware side there are issues like electromagnetic interference and quality of fault tolerance that still influence the integrity of the digital datasignal. Manufacturers all have various ways to handle these, again resulting in differences.
It's only at the DVI/HDMI output that the digital signal is "final".

These differences are all tiny, but they all add up to a somewhat bigger difference between various players. It's true that most people won't see it, especially since they don't compare multiple sets side by side.

With respect, Fireshade, I agree that coding skill applies to decompression speed but having researched this, as far as I can tell it does not apply to quality. Not even with jpeg. If an image has been compressed to jpeg standards (and I agree you can make all sorts of choices at the point of compression) with decompression every jpeg decompressor will extract exactly the same image.

If post-processing is then taking place to modify the image before handing on to the display then I can understand there being a difference, I'd appreciate it if anyone has any pointers to manufacturer claims or technical algorithms for my education.

As to electromagnetic intereference and digital integrity, I would point out that the text from this website manages to cross the internet, through your ISP down your ADSL line and get onto your screen without introducing different random corruption every time the page is loaded, so moving bits three feet from a DVD/Blu-ray to a display is a walk in the park by comparison. Digital error management and correction is a well understood process.

I think you are right about PureVideo doing more than just moving bits but PureVideo on a PC is part of the display function, and I have agreed that different displays will process digital picture info each their own way.

My worry is that this "sort of" understanding is common. I believe we all have this expectation that it should matter from the analogue days more than it does in the fully digital domain.

You and Bailey's_Coffee have my thanks for pointing out that digitial domain "picture enhancement" functions may be responsible for the differences and all being well I will try and take Bailey's advise to go and look for myself when possible.

Thanks again

Crash

@Crash Biker...

I know exactly where you're coming from - the word 'digital' implies many things... including precision and a result that is impervious to anomalies.

But there can be huge differencies in practice (much like 2 different models of laser printer often produce quite different looking printed results from the same source PCL spool file due to many factors, including differences in greyscale rendering, font smoothing, engine resolution, unprintable area, toner density, drum material, toner particle size, etc, etc).

Sometimes you just have to see these things first hand to gain a fuller picture of things - and an appreciation of how theory is often skewed by the manner in which a particular technology is implemented... and not always for the better either.

;-)

@Crash Biker:
I understand your point about the "exact decompression" result, but with lossy formats decoding can still vary. This flexibility has been built in by the lossy codec standards.
They take into account that there are different quality needs. If speed is paramount, then (decoded) image quality takes a backseat. The standards allow several parameters, and decoders don't all use the same rules. Decoding also contains requirements for accuracy - meaning that the decoding algorithm can vary in output accuracy.
E.g. for H.264 and VC-1 there is a maximum accuracy of 1/4 pixel for motion compensation and minimal reference blocks (all meaning they may be bigger = less sharp, all up to the manufacturer).
Lossy format decoding will therefore not always produce the same results.

Since in video speed is paramount (uninterrupted motion and sound is more important to the experience than image quality), algorithm and chip designers will make trade offs with decoding quality.
Cheaper players will use cheaper decoding hardware that is less powerful in decoding, and post-processing will be done with less developed/clever software to handle issues such as motion compensation, anti-aliasing and artefact reduction.

I hope this helps clarifying the duality of digital data :)