Why IMX477 2x2 sensor binning mode is a crime and should be rendered illegal (now that we have a way around it).

 OK. That's a bold statement. So, we need proofs. Here we go !

This first picture is captured using the infamous 2028x1080 mode:

2028x1080 aka 2x2 sensor binning

 

Now, the same picture, with the same lens and same setting, but captured with the sensor full resolution and scaled down to 2028x1080:

4056x2160 scaled down to 2028x1080

OK, at those sizes, depending on what device you are reading this, it might not be obvious (using a 28" 1080p TV as screen, at less than 1 meter, it is way too obvious), so here is a 480x270 crop inside both pictures to make my point clearer (pun intended):

2x2 binned zoom

full sensor scaled down zoomed

 

There is so much details lost on the 2x2 sensor binned version that it manages to hide the chromatic aberration from the lens. Both pictures where captured with an IMX477, connected to a 2GB Pi 5, with an HSs18x5.5BMD lens, with the following settings: Zoom=5.5mm, Iris=f/5.6, Focus=Infinity

Rule of thumb: always capture the full sensor resolution. The "debayer" process will be able to recover every possible detail. Then, scale down the image. By binning the "pixels" at Bayer's level, sharp edge details are lost forever.

OK, but if you are using the Pi HQ Camera for video on a Raspberry Pi (even the at-the-time-of-writing new Pi 5 with its full-blown 4-lane MIPI interface), you have no choice but to stick with the 2028x1080 mode, right ?
The basic 2-lane MIPI will clamp you to about 10 fps. But if you read the IMX477 datasheet, it can output 4K 60fps on 4 lanes, so 4K 30fps should , at least, be possible with only 2 lanes. Well is turns out the IMX477 does its magic thank to a 2.1Gbps speed on the MIPI lanes, while on Raspberry Pi the sensor CSI-2 interface is clocked much lower (900MBps, at least for EMC and power considerations). So, maybe someone had hacked its way through the speed limit.

Then, looking back at the Raspberry Pi forum for any news on 4-lane IMX477 support (I perfectly understand the Foundation has no reason to support it, because their HQ Camera has only 2 lanes), I indeed stumbled upon this: https://forums.raspberrypi.com/viewtopic.php?t=371216

The results are incredible:

pi@bookworm64:~ $ rpicam-hello --list-cameras
Available cameras
-----------------
0 : imx477 [4056x3040 12-bit RGGB] (/base/axi/pcie@120000/rp1/i2c@80000/imx477@1a)
    Modes: 'SRGGB10_CSI2P' : 1332x990 [254.45 fps - (696, 528)/2664x1980 crop]
                             2028x1080 [146.41 fps - (0, 440)/4056x2160 crop]
                             2028x1520 [104.05 fps - (0, 0)/4056x3040 crop]
                             4056x2160 [38.87 fps - (0, 0)/4056x3480 crop]
                             4056x3040 [27.62 fps - (0, 0)/4056x3040 crop]
           'SRGGB12_CSI2P' : 1332x990 [212.04 fps - (696, 528)/2664x1980 crop]
                             2028x1080 [122.00 fps - (0, 440)/4056x2160 crop]
                             2028x1520 [86.70 fps - (0, 0)/4056x3040 crop]
                             4056x2160 [32.39 fps - (0, 0)/4056x3480 crop]
                             4056x3040 [23.02 fps - (0, 0)/4056x3040 crop]

Now, using this overclocked version of the imx477 driver, you can get 4056x2160x12 at a stable 30fps ! Then scale down to 1080p and H264 encode the result, for as sharp a 1080p can be.
And if you don't care about image quality, and have a lot of light, you can even play with the 10-bit 1332x990 mode, running flawlessly at 240 fps (don't try to H264 encode this, though, use MJPEG instead).