What if you had no CFA at all? (Just curious)

[cathexis]

Imagine a digital camera were made and they left the CFA out. What would the photos look like?
I suppose there might be a quibble that the software "needs it" so you'd get an error rather than
a photo. But I'm asking as if that weren't an issue. Would the pic be B&W? Washed out gray?
Dimly colored? CFAs seem to be essential to the making of a color digital photo but they seem to
be irrelevant as far as the original illuminant is concerned so I'm just curious but would appreciate your thoughts.

TIA,

Andrew

 

[480sparky]

What you would see depends on where you look at it.

In order to display the image on the camera's monitor, the raw file produced by the sensor would have to be demosaiced. I don't think there's a single camera that's capable of by-passing this. You'd end up with a checkered image of distorted colors.

However, if you shot in raw format and imported the file into software that's capable of not demosaicing the data, you'd have a very detailed b&w image.

Imagine a digital camera were made and they left the CFA out.
...........

No need to imagine. Leica makes one. They're $8000.

 

[Braineack]

just run it through reddit's colorizing algorithm

colorz made from silicon neuronz • r/colorizebot

 

[KmH]

This

Would look like this

 

[Ysarex]

Imagine a digital camera were made and they left the CFA out. What would the photos look like?
I suppose there might be a quibble that the software "needs it" so you'd get an error rather than
a photo. But I'm asking as if that weren't an issue. Would the pic be B&W?

Yes.

Washed out gray?

No. The Leica Monochrome is a digital camera without a CFA. It takes great B&W photos. The sensor data must still be processed since the sensor's tonal response is strictly linear, but this is not a CFA issue.

Dimly colored?

No color.

Joe

CFAs seem to be essential to the making of a color digital photo but they seem to
be irrelevant as far as the original illuminant is concerned so I'm just curious but would appreciate your thoughts.

TIA,

Andrew

 

[cathexis]

Thanks good people!

 

[480sparky]

I didn't have time earlier to expound as much as I wished on my first post.

Leica's camera is specifically designed for B&W since it has no color filers in front of the sensor. So 1 sensor pixel = 1 image pixel. Pretty straight-forward.

But the rest of the digital cameras out there have a CFA. This means in order to create a color image, the software must take the data that comes from one red pixel, one blue pixel and two green pixels. It then combines this data into one image pixel with all three colors assigned to it. RGB. So much red, so much green, so much blue.

Now, if you were to magically reach in and pull the CFA out of the camera, your onboard processor would still demosaic the image since there's no way to 'program' it to do otherwise.

So I'd say you'd see a very distorted color image on the monitor. It would also most likely be overexposed some as the CFA, just like any other color filter, reduces light transmission. With no CFA in place, more photons would reach the sensor. So you'd have to alter your EC some to correct for that. Once you're back to a 'correct' exposure, you'd still have a distorted color image as the demosaic algorithm in the camera is still trying to process the data to create a color image, but with no CFA there is no color. Just luminosity.

But, if you were to shoot in raw format, and import the file into a processor that can bypass any demosaicing, you'd have a black & white image.

 

[TCampbell]

You'd get a monochrome image. The RAW file is technically a monochrome image but (assuming the CFA is a Bayer matrix) you'd get a wonky b&w since the filters only allow light transmission for their particular color bandwidth. So I'm taking a photo of say, a "red" fire truck, all the photo sites that represent "red" would appear "white" in the monochrome image and the photo-sites that represent "green" and "blue" would appear as "black" in the monochrome image.

The de-bayer (sometimes called de-mosaicing) process typically takes each photosite and compares it to the light intensity of its neighbors to derive the final blended RBG color. So if I have a "red" photosite but the neighboring "green" and "blue" photosites are black (no light) then it assumes pure red should win and you get the "red" pixel. But suppose the "blue" photo sites were also white but the "green" were still black. It would blend the red & blue to derive a "violet" color in RGB. It turns out there's more than one algorithm to de-bayer an image. The software you use to process your RAW files decides how it will be done. This is why you can open the same RAW file using different programs and upon close inspection you'll find that the pixel values are not actually identical (though they probably will be close).

In astrophotography there are a number of photographers who shoot with a monochrome CCD camera to produce color images (I just got such a camera... but the weather hasn't been good enough for me to use it yet.) Anyway, you can then get a filter-wheel... a device that attaches between the scope & camera. The filter wheel is typically has a minimum of 5 positions (some have more). One position is left blank (straight through shooting without a filter), and the remaining four are loaded with a "red", "green", "blue", and "luminance" filter. The red, green, & blue are obvious... a "luminance" filter is really a combined UV & IR filter... it allows the full "visible" light spectrum to pass (hence "luminance") but blocks non-visible wavelengths (it allows wavelengths from 400 through 700nm).

To use such a camera, you shoot one (or more) images with each filter. You can open these in Photoshop (or whatever your favorite processing app happens to be), and where you normally see the "layers" list in Photoshop, you click the tab to take you to the "channels" list. You open the image you shot with the "red" filter and assign it to the "red" channel. The same for blue & green. When you then flip back to the RGB channel, you'll notice that you now see a full color image even though you shot everything in monochrome.

This works for astrophotography because the camera is attached to a telescope on a mount which is accurately tracking the sky (compensating for the movement of the Earth). So for photographic purposes... nothing in the image is moving and you can capture hours worth of images.

If you were doing this with normal photography, you'd need a tripod and you'd need to be photographing a scene where nothing is changing.

 

[cathexis]

Thanks to you both for your f/up replies,

Tim, I wonder if you're on the Cloudy Nights forum. If you aren't you should be. I find the whole subject of AP to be fascinating to see the results of,
but damnably expensive & frustrating to practice. That's why I'm a devout Visual-only amateur. And that bit about, "accurately tracking" - easy words,
unholy to actually do with much less than at least a Losmandy GM-11, and ideally even more. I'd be in a dream to "just" have a Tak 120 on a used
GM-11 in my lite-polluted skies. Visual-only preserves sanity. Kudos for you for trying AP !

Back to the thread. I wanted to ask as follow up: So how would Colored Filters & ND filters affect the CFA? Are there creative possibilities there ?
Or just making a mess of things? I know that colored filters are really more for B&W film.

Thanks!

Andrew

 

[Ysarex]

Thanks to you both for your f/up replies,

Tim, I wonder if you're on the Cloudy Nights forum. If you aren't you should be. I find the whole subject of AP to be fascinating to see the results of,
but damnably expensive & frustrating to practice. That's why I'm a devout Visual-only amateur. And that bit about, "accurately tracking" - easy words,
unholy to actually do with much less than at least a Losmandy GM-11, and ideally even more. I'd be in a dream to "just" have a Tak 120 on a used
GM-11 in my lite-polluted skies. Visual-only preserves sanity. Kudos for you for trying AP !

Back to the thread. I wanted to ask as follow up: So how would Colored Filters & ND filters affect the CFA? Are there creative possibilities there ?
Or just making a mess of things? I know that colored filters are really more for B&W film.

Thanks!

Andrew

ND filters should do what ND filters are designed to do and only alter exposure -- no concern for the CFA. Tone adjusting color filters for B&W aren't going to work as intended -- it's a color image and there's really nothing you can do about that. So the classic B&W yellow filter for a darker sky is just going to add a yellow tint to your color image. What we used to do with those filters in the field we can now do in editing since we have the original color image. All those effects from a red filter to turn a blue sky black to a green filter to tan up a rugged looking fellow are all available in the conversion process to generate a B&W image. In fact it's a whole lot better now that's digital because you can split the filtering to different sections of the photo. Here's an example:

Joe

 

[TCampbell]

Thanks to you both for your f/up replies,

Tim, I wonder if you're on the Cloudy Nights forum. If you aren't you should be. I find the whole subject of AP to be fascinating to see the results of,
but damnably expensive & frustrating to practice. That's why I'm a devout Visual-only amateur. And that bit about, "accurately tracking" - easy words,
unholy to actually do with much less than at least a Losmandy GM-11, and ideally even more. I'd be in a dream to "just" have a Tak 120 on a used
GM-11 in my lite-polluted skies. Visual-only preserves sanity. Kudos for you for trying AP !

Back to the thread. I wanted to ask as follow up: So how would Colored Filters & ND filters affect the CFA? Are there creative possibilities there ?
Or just making a mess of things? I know that colored filters are really more for B&W film.

Thanks!

Andrew

I only occasionally visit Cloud Nights. I spend more time on Astronomyforum.net. I've been through the frustration of trying to get accurate tracking with several mounts. Fortunately I've also experienced the joys of having the equipment actually work (for a change) and it was really encouraging. Don't give up!