clouds are back. As i have some free time, i tried something new with my colour camera : try to change it into a monochrome camera.
My sensor (IMX485) is a bayer sensor (to get colour information).
Colour is extract from 4 pixels. In my case, the order is :
So, 1 red pixel, 2 green pixels (G1 & G2) and 1 blue pixel.
For sure, photosite doesn’t get the entire signal (only red, or green, or blue). That’s why colour sensor are about 1/3 sensitive as mono sensor (which gets the entire signal).
Most time, you can get grey image with a colour sensor. The camera applies a small calculus like :
Luminance = Red0.2126 +Green0.7152+Blue*0.0722 (or something like that). In that case, the result intensity is quite the same result you will get with the colour image.
Let’s try something different :
Luminance = R + (G1+G2)/2 +B
Quite simple. So, let’s see the result.
First, the classical colour image (gain 100, exposure 11ms) :
Now, the classical grey transformation. The luminance is the same :
Now, the new transformation, which is supposed to raise the luminance :
As you can see, it works quite well.
What would be the camera setting to get the same luminance with classical grey transformation ?
To get the same result, the exposure time must be 43ms (compare it to the 11ms exposure time with the new transformation).
It is the same with colour image :
So, with the new grey transformation, i can get much more signal than the normal signal i can get with the colour sensor. I must say i always use the sensor information so i don’t bring false information).
With this method, i will be able to make deep sky survey video with (much) lower exposure time (for example, 100ms exposure time instead of 300-400ms exposure time) and keep my colour sensor instead of buying a new monochrome sensor camera.
For sure, i will lost the colour. As deep sky survey means quite long exposure time, i guess i could colourize my monochrome capture with the RAW colour image. Just have to verify that.
An important thing to say : monochrome sensor is better for resolution and details (1 pixel for the mono sensor, 4 pixels for the colour sensors). I can’t make miracles each time.
Well, that’s all. Clear sky !