Tuesday, May 8, 2018

Sony A8F vs LG C8

Despite the picture quality on the Sony A8F and LG C8 being nearly identical with most SDR content (due the same latest generation OLED panel being used in both the A8F and C8), it should be said that there are some differences due to processing. For example, the Sony A8F has a slight edge over the LG C8 when it comes to upscaling very low resolution content (e.g. Standard Definition), removing banding artifacts in low bitrate content, and performing a motion interpolation of such content. The LG C8, on the other hand, can get a bit brighter than the Sony A8F in small specular highlights with HDR content, as well as to provide more brightness headroom with mid-to-high APL content in SDR mode. The input lag is lower on the C8 vs A8F, and all 4 HDMI inputs on the LG C8 are full-bandwidth whereas the Sony A8F has only two HDMI version 2.0 ports (out of 4). The LG C8, however, lacks any USB 3.0 ports (but it has three USB 2.0 ports, though) while there is one USB 3.0 port on the Sony A8F (and two USB 2.0 ports).

Image Processor
The A8F utilizes the Sony X1 Xtreme chipset whereas the C8 relies on the LG Alpha 9 processor. Generally, both chips are powerful enough for the Sony A8F and LG C8 to be able to perform a number of advanced picture quality enhancements. That being said, there is a difference in how some of these features are implemented. For example, there is a dedicated setting for Smooth Gradation on the Sony A8F which allows for banding to be removed from low bitrate content which is somewhat prone to exhibiting contouring artifacts due to quantization errors. Although the LG C8 is also equipped with decontouring filters, they are used in conjunction with temporal noise reduction filters (for a total of a quad step MPEG noise reduction process), meaning that you cannot have smooth gradation without also reducing temporal noise, which may lead to some detail loss. Therefore, the Sony A8F has a certain advantage over the LG C8 in terms of low bitrate content which extends to low resolution content as well due to the dual database processing capability on the A8F's X1 Xtreme chipset, and more precisely: having access to the tens of thousands picture patterns that comprise each of two Sony's propriety databases: for upscaling and noise reduction. That being said, with HD or FullHD content (with adequate bitrate), the difference between the A8F and C8's upscaling is minimal. When it comes to SDR-to-HDR upconvertion, the Sony A8F applies Object-based HDR remaster across most of the SDR picture presets whereas the LG C8 has a dedicated HDR effect mode. That being said, the C8 also has an Object depth enhancer in certain picture modes, meaning that it's also able to enhance both the sense of depth and the detail in textures.

SDR (Standard Dynamic Range) content
Except for mid-to-high APL (Average Picture Level) content, the difference caused by the ABL (Auto Brightness Limiter), which is used on both the A8F and C8, is minimal. Considering that most SDR content has low-to-mid APL, the Sony A8F and LG C8 therefore have identical brightness headroom in case you plan to watch SDR movies and TV series under bright lighting conditions. Only when it comes to mid-to-high APL content, such as hockey, the C8 has a slight advantage over the A8F due to the more relaxed ABL which allows for higher brightness to be achieved with such content. Nevertheless, both the Sony A8F and LG C8 are able to reach and exceed the 100cd/m2 SDR content is typically mastered to, even on a full-filed white (100% APL).

HDR (High Dynamic Range) content
Due to some differences in the ABL (Auto Brightness Limiter), the LG C8 is able to render highlights in HDR content approximately 100cd/m2 brighter than the Sony A8F. The LG C8 can reach up to 900cd/m2 in small specular highlights whereas the Sony A8F: up to 800cd/m2 when neutral color temperature is used. This means that neither of the two OLED TVs is able to completely avoid tone-mapping, even with HDR10 content that has been mastered to 1,000cd/m2. Both the A8F and C8 are able to generate dynamic metadata on the fly in order to avoid the unnecessary darkening of the entire image during scenes with no highlights that HDR10 content is prone to due to the maxCLL, which static metadata defines, remaining the same for the entire content duration, irrespective of whether the scene contains highlights or not. Dolby Vision content, on the other hand, is optimized on a scene by scene basis thanks to the inclusion of dynamic metadata. The LG C8 supports Dolby Vision out of the box whereas the Sony A8F requires a firmware update for this HDR format. When it comes to HDR10 and HLG (Hybrid Log Gamma), there is no difference between the A8F and C8 since both formats are supported out of the box.

Auto-calibration (only LG C8)
The LG C8 provides the CalMAN software by SpectraCal (sold separately) with a direct access to its internal color LUTs (look-up tables). The 1D LUT contains 1024 data points, and is used in process of auto-calibrating the grayscale and gamma. The 3D Cube LUT on the C8 has a 33x33x33 resolution, meaning that it can store 35,937 color data points that can be looked-up directly, in addition to being used as a reference when the coordinates of any color without predefined data point are calculated. The Sony A8F doesn't provide access to its internal LUTs to the CalMAN software, meaning it cannot be auto-calibrated.

Motion & Input lag
The Sony A8F has a slight advantage over the LG C8 in terms of motion interpolation, especially when used with lower resolution content. This technique intends to make motion smoother by the means of generating intermediate frames and inserting them between the original ones. Other than that, the motion performance is mostly on par between the A8F and C8. The reason being is that they have the same native refresh rate of 120Hz (which means a new frame is drawn every 8.3ms), in addition to the same nearly instantaneous pixel response time (which allows the OLED pixels on the A8F and C8 to finish transitioning before the next refresh cycle, hence the lack of any dark trails or ghost afterimages following fast moving objects). Furthermore, both the A8F and C8 have an optional black frame insertion which allows them to remove motion blur caused by the fact that every frame is hold for 8.3ms without any interruption in the light output which causes fast moving objects to appear blurred across frames. The input lag on the LG C8 is approximately 21ms (with either 4K or 1080p @ 60Hz signal), whereas the Sony A8F takes about one frame longer to react to your input when 4K signal is used, meaning the input lag is close to 31ms. With 1080p @ 60Hz signal, the A8F registers your input approximately 3 frames later than the C8, meaning there is even more delay than with 4K signal.

Although the Sony A8F and LG C8 have 4 HDMI inputs each, it should be said that there is a difference in the number of full-bandwidth inputs (as far as the HDMI 2.0 goes). The A8F has only 2 full-bandwidth HDMI inputs vs 4 HDMI inputs on the C8 being full-bandwidth. The HDCP 2.2 is supported on all HDMI ports on both TVs. When it comes to HDMI 2.1, however, neither the A8F, nor the C8 have any such ports, meaning that they cannot accept 4K @ 120fps via HDMI. That being said, the C8 is equipped with a HEVC decoder that conforms to the Main10 profile at level 5.2, meaning it supports 4K HFR (High Frame Rate) content, albeit only via USB. Speaking of which, there are three USB ports on the Sony A8F and LG C8. All USB ports on the C8 are USB 2.0 whereas the A8F has one USB 3.0 port, in addition to the two USB 2.0 inputs.

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