Image darker at ISO 200 than ISO 100

[Austriker]

Hi,

I have been testing Picamera with a fixed shutter_speed. And taking 7 pictures with the 7 ISO. But the picture at ISO 200 is darker than the image at ISO 100. Is it normal ? Did I missed something ?

I use video_port=True to try to remove the cyan vignetting, that appears in Full Frame.

Here is the code that I use :

#!/usr/bin/env python3
import picamera
import time

camera = picamera.PiCamera()

camera.exposure_mode = 'auto'

camera.resolution = (2592, 1944)
camera.framerate = 5

iso_list = [100, 200, 320, 400, 500, 640, 800]

camera.shutter_speed = 1185

for i in range(0, len(iso_list)):

    camera.iso = iso_list[i]

    camera.capture(
        img_name,
        use_video_port=True,
        format='jpeg',
        quality=100,
    )

    print("Image {0} taken !".format(img_name))
    time.sleep(1)

Thanks

[6by9]

Which revision of camera board is this with? Lens shading (cyan vignetting) should be fixed on the V2 sensors, with an option to try the same fix on V1 (add ov5647_acls=1 to boot/config.txt). Or you can use still_stats=true to also avoid it. Please use one option or other to other to use the stills port, as that will insert a load more debug into the JPEG, and then post the JPEGs somewhere useful.

Alternatively retrieve the analog_gain, digital_gain, and exposure_speed for each of your captures.

The only values actually supported are 100, 200, 400, and 800. All others will round to the nearest of the supported list.

[Austriker]

The camera board is a v1.3 I used a clean raspbian jessie image 2015-09-24-raspbian-jessie then I did :

sudo apt-get update
sudo apt-get upgrade
sudo apt-get dist-upgrade

But I didn't do a sudo rpi-update

Here is the script I used for the tests :

#!/usr/bin/env python3
import picamera
import time
import datetime
import os

camera = picamera.PiCamera()

camera.exposure_mode = 'auto'

camera.resolution = (2592, 1944)
camera.framerate = 5

# camera.still_stats = True # for the second test

iso_list = [100, 200, 400, 800]

camera.shutter_speed = 5000

folder = '/home/pi/' + datetime.datetime.strftime(
    datetime.datetime.now(), '%Y-%m-%d_%H-%M-%S_SS15'
)
os.makedirs(folder, exist_ok=True)

for i in range(0, len(iso_list)):

    camera.iso = iso_list[i]

    img_name = os.path.join(folder, '{0}_{1}_{2}.jpeg'.format(
            datetime.datetime.strftime(
                datetime.datetime.now(), '%Y-%m-%d_%H-%M-%S'
            ),
            camera.iso,
            camera.shutter_speed
        )
    )

    camera.capture(
        img_name,
        format='jpeg',
        quality=100,
    )

    print("Image {0} {1} {2} {3} taken !".format(
        img_name,
        camera.analog_gain,
        camera.digital_gain,
        camera.exposure_speed
    ))
    time.sleep(1)

The first test is with the use_video_port=true : test folder 1

Image /home/pi/2016-05-03_14-50-18_SS15/2016-05-03_14-50-18_100_1154.jpeg 1 1365/256 1154 taken !
Image /home/pi/2016-05-03_14-50-18_SS15/2016-05-03_14-50-20_200_1154.jpeg 19/16 411/256 1154 taken !
Image /home/pi/2016-05-03_14-50-18_SS15/2016-05-03_14-50-21_400_1154.jpeg 33/16 455/256 1154 taken !
Image /home/pi/2016-05-03_14-50-18_SS15/2016-05-03_14-50-22_800_1154.jpeg 33/8 109/64 1154 taken !

The second test with camera.still_stats = True and i removed this option use_video_port=true: test folder 2

Image /home/pi/2016-05-03_14-52-05_SS15/2016-05-03_14-52-05_100_1154.jpeg 1 281/256 1154 taken !
Image /home/pi/2016-05-03_14-52-05_SS15/2016-05-03_14-52-08_200_1154.jpeg 19/16 257/256 1154 taken !
Image /home/pi/2016-05-03_14-52-05_SS15/2016-05-03_14-52-10_400_1154.jpeg 15/8 71/64 1154 taken !
Image /home/pi/2016-05-03_14-52-05_SS15/2016-05-03_14-52-12_800_1154.jpeg 31/8 275/256 1154 taken !

I did the same test with the option ov5647_acls=1 but it doesn't remove the vigneting. The first test shows the defect at ISO 200 and at ISO 100 the image is really weird. But with the second test the pictures works properly and the vigneting seems to disapear.

[Delgan]

I made some tests with the new camera V2.1 and I can confirm @6by9 words, whatever the values of still_stats and use_video_port was, I did not notice any cyan vignetting.

Moreover, the iso parameter was acting as expected and I did not encounter weird behavior: the image brightness looked to enhance while iso was increasing (except maybe for iso 100/200 with use_video_port=true which look the same).

Images resulting from these tests can be see here:

• camera.still_stats=False, use_video_port=False
• camera.still_stats=True, use_video_port=False
• camera.still_stats=False, use_video_port=True
• camera.still_stats=True, use_video_port=True