Can Blu-ray Movie Picture Quality be Measured Digitally?

Question:
When you review Blu-ray movies for picture quality is it possible to also show if the Blu-rays pass 3:2 pulldown, and have chroma issues, like when you review Blu-ray players? Basically have a digital way of measuring how good the picture quality is on a Blu-ray movie? This way we could find the ultimate Blu-ray for picture quality.

– Carl M
Wake Forest, NC

Answer:
When we review Blu-ray discs here at Secrets we always comment on picture quality in terms of what we see but as far as we know, there is no way to perform a measurement that rates one transfer over another.

Let’s look at the issues you mention individually. 3:2 pulldown is a process whereby 24fps film content is processed so it can be shown on a display running at 60Hz or 60fps. Obviously 24 does not divide evenly into 60 so the individual frames must be repeated in an alternating pattern of 3 and 2, hence the term “3:2”. This is a process carried out by either your Blu-ray player or your display.

Most of today’s Blu-ray players can output film content at either 60 or 24fps. The choice is determined by the capabilities of your display. An LCD that runs at 120Hz can correctly process 24fps content by simply repeating each frame five times. This is an essentially perfect representation of the original film framerate. If your TV cannot do this, it will use the 3:2 processing to convert the 24p signal to 60Hz then double the frames if 120Hz is the panel’s native refresh rate.

Whatever equipment you may be using, the 3:2 processing quality is not determined by the Blu-ray disc. The content is simply encoded at 24p and it’s up to your player and display to correctly process the signal. With progressive encoding of today’s Blu-ray discs, it’s nearly impossible to create an error situation that can’t be handled by any Blu-ray player or display.

Chroma, and I’m guessing you mean chroma upsampling, is also a video processing issue. When content is encoded on a Blu-ray disc, it’s stored in a 4:2:0 component video format. This approach, along with sophisticated compression techniques, is what makes it possible for a three-hour movie scanned in 1080p resolution along with up to eight discrete audio channels to fit on a 50Gb optical disc.

Chroma upsampling occurs when the player converts the 4:2:0 component signal to at least 4:2:2 bit-depth before sending it out to your display. Many players can also output a fully upsampled 4:4:4 signal or even RGB. YCbCr 4:4:4 is probably the best choice.

Again, this is not a function of the disc’s encoding but of the player and display’s processing capabilities. It is possible for a disc to have compression artifacts like color banding or jaggies; and this is certainly something we would note in a Secrets movie review.

Most of our comments concerning Blu-ray image quality go back to the original content. Is detail sharp? Is color well-saturated, or flat and drab? Is the contrast range broad with deep blacks and bright whites, or is there clipping of highlight and shadow detail? These are the factors we look for in determining Blu-ray picture quality. Video processing has essentially become a moot point now that things like scaling and de-interlacing are needed less often. When the content and the display can match resolution and framerate; all that is necessary is for the player or display to convert the component signal to RGB. And again, that is not an issue found in the disc encoding process.

For now at least, it seems that rating Blu-ray picture quality must remain a subjective matter. Unless specific issues present themselves, we will continue to comment on color quality, contrast and overall clarity.