[HOW-TO] speed up still image capture_array?

Start with the capture_array.py example and the Picamera2 capture_array entry point, then reproduce the reported 0.12-second timings using the shown still configuration on the Raspberry Pi Camera Module 3. Compare the measured behavior with the requested 480x270 output and determine whether a supported configuration change can improve it; document the result and evidence when done.

Hi there, I'm using a Raspberry Pi Camera Module 3 with a Raspberry pi 4b. I'm trying to capture still images with the full field of view of the camera, but then scale them down to a smaller size. I'm trying to do this as fast as possible.

Here's my code:

import picamera2
import time

picam2 = picamera2.Picamera2()
config = picam2.create_still_configuration(
    main={"size": (480, 270)}, # scale down the 4608x2592 image, but maintain the full field of view
    raw={'size': picam2.sensor_resolution}, # 4608x2592
    buffer_count=2
)
picam2.configure(config)
picam2.start()

while True:
    loop_start = time.time()
    output_orig = picam2.capture_array()
    img_capture_elapsed_s = round(time.time() - loop_start, 3)

    print(f"Image capture took {img_capture_elapsed_s} s. {output_orig.shape}")

I'm seeing capture_array performance timings of about 0.12 seconds. Is there any way to speed this up, or is this as fast as it goes? Here are the logs that this program generates:

% python3 capture_array.py
[1:10:13.600190093] [2801]  INFO Camera camera_manager.cpp:297 libcamera v0.0.5+83-bde9b04f
[1:10:13.717678717] [2804]  INFO RPI vc4.cpp:437 Registered camera /base/soc/i2c0mux/i2c@1/imx708@1a to Unicam device /dev/media4 and ISP device /dev/media1
[1:10:13.717763491] [2804]  INFO RPI pipeline_base.cpp:1101 Using configuration file '/usr/share/libcamera/pipeline/rpi/vc4/rpi_apps.yaml'
[1:10:13.725368945] [2801]  INFO Camera camera.cpp:1033 configuring streams: (0) 480x270-BGR888 (1) 4608x2592-SBGGR10_CSI2P
[1:10:13.726000376] [2804]  INFO RPI vc4.cpp:565 Sensor: /base/soc/i2c0mux/i2c@1/imx708@1a - Selected sensor format: 4608x2592-SBGGR10_1X10 - Selected unicam format: 4608x2592-pBAA
Image capture took 0.693 s. (270, 480, 3)
Image capture took 0.12 s. (270, 480, 3)
Image capture took 0.12 s. (270, 480, 3)
Image capture took 0.119 s. (270, 480, 3)
Image capture took 0.12 s. (270, 480, 3)
Image capture took 0.122 s. (270, 480, 3)
Image capture took 0.118 s. (270, 480, 3)
...

Thanks!