Massively confused with Trichrome on a digital camera.

Started 2 months ago | Questions thread
MCLV Senior Member • Posts: 1,139
Re: Massively confused with Trichrome on a digital camera.

Tom Axford wrote:

CamFiasco wrote:

Tom Axford wrote:

If you want to emulate the three-colour process on a digital camera, you need no filters at all because they are already present in the sensor. If you shoot a raw image, then it saves the data separately from the red, green and blue-sensitive pixels in the camera. If you want to get the R, G an B data out of the raw file, I am not sure, but probably software such as Rawdigger may do that for you.

Otherwise, you could easily separate out the R, G and B data from a JPEG image, but that RGB data is not exactly the same as the raw data because it has already been converted into a standard colour profile such as sRGB. However, it may be acceptable for your purposes, depending on exactly what you are trying to do.

Not exactly, I want to emulate the 3 color process that looked like technicolor, in fact I have actually shot such RGB mix with my film camera, and I want to see how different it looked out of a digital sensor, but at the moment I'm not really grasping the reason why from a Bayer RGB sensor would look so much different from a monochrome( film) or sensor...

Modern film stock has three color sensitive layer stacked on top of each other, which is what Sigma Foveon equivalent to digital sensors. that's one of the reasons why the dye transfer/ Technicolor or Trichrome looked so different from say... Kodak Potra...

So if bayer layer is just RGB in a matrix, then why can't I consider it as with a blue filter on top, I'm just taking a photo with only the blue pixels receiving light, while (for the most part) blocking out Red and Green?

Sure there twice as much Green in the Bayer matrix, but that only means pixel count and resolution, nothing to do with exposures

sure the three colors have overlap as show on your graph... but not as wild as what I got here...

I begin to suspect that it's the light metering system that is causing this( blue filter gives -4 stop reading as opposed to 2 1/3 filter factor), perhaps due to something to do with the amount of pixel receiving light...?

If you are using tricolour filters in front of the lens, you need to treat the camera as monochrome and use software to convert the RGB digital image to monochrome in a consistent way for the three separate images you get from the three filters.

The white balance must be fixed (not auto) and the same method of converting to monochrome must be used for all three images. The grey scale image is a weighted average of the red, green and blue channels. If the result is not a good match to technicolor, then you can change the weightings of the red, green and blue channels to improve it.

The aim is to essentially make the spectral response of your "monochrome" digital camera as close as possible to that of the film used for technicolor. A perfect match probably isn't possible, but you should be able to get reasonably close. However, I think it is probably very hard to do without using specialist equipment.

When I looked up trichrome photography, I found out that the same color filters were used during capture and projection of the images. Since Bayer CFA and display color filters are not the same as ones that are used for trichrome capture, converting each exposure to monochrome and assigning it to one color channel will distort colors, won't it?

Instead, it we assume that we have calibrated camera and display and that such system can faithfully capture perceived color, images shouldn't be converted to monochrome but simply stacked in their original form as sybersitizen proposes here:

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