Sony F-828 Raw Digger 3-channel raw composite vs. 4-channel raw composite

[Andrea B.]

ADDED LATER:  I'm showing first how the Raw Digger app behaves with a typical RGGB camera. (Might be RGBG, not sure.) Then I have results for the unusual old Sony F-828 R,G,B,"Emerald" camera.

 

Here is a photo I made of the Color Checker Passport to use for making a color profile in Photo Ninja for visible work from my full spectrum D600. I used the UV-Nikkor filtered by a Baader UVIR-Cut stacked with a B+W BG38. You can see some little pink flowers peeking out from behind the Passport. That is a Houstonia rubra which I was photographing that day. The raw file was converted in Photo Ninja where the color profile I made from this Passport was applied.

Color Profiled, White-balanced Visible Image

 

 

 

Here is the Raw Digger raw composite of that photo  showing how the data looked before white balance was applied. I selected the 3-channel output option from Raw Digger. This averages the two green channels which are almost identical for a D600. Then the R, B and averaged G channels are "stacked" in the usual manner to produce the raw composite. As I've mentioned before, a raw composite is not a pretty thing. A visible raw composite from an R,G,G,B camera will have a green-ish cast because no white balance has been applied. Only demosaicing, scaling and a gamma curve have been applied to the raw data. This is not a "finished" image. 

Raw Composite with 3-Channel Option

 

 

 

If I output a raw composite of a D600 file and do not select the 3-channel option, then all four R, G, G, and B channels are stacked. If you have ever played around with stacking images (think "difference" layer stacking in PS), then you know that stacking 4 channels gives an "inverted" look because any color in the 4th layer is going to diff with that color in one of the other layers to produce darks where lights are expected and v.v.

4-Channel Raw Composite

 

 

 

To give that 4-channel raw composite a normal (relatively normal, that is) look, we have to invert it. The result is brighter than the 3-channel raw composite above but still has that green-ish cast because no white balance has been applied.

Inverted 4-Channel Raw Composite

 

 

 

Now let's look at an image from the Sony F-828 which has this unusual set of 4. channels: Red, Green, Blue and "Emerald". The "Emerald" channel was intended to match the way human eyes see green, so I have read. The image here is an IR image made by VideoJohn and originally posted here: LINK. John kindly lent me some raw SRF files from the Sony F-828 to play with.

IR Image from Sony F-828

 

 

 

When Raw Digger creates a raw composite from an SRF file, it does not offer the 3-channel option because it does not make sense to "average" the two green channels which have different greens. So a 4-channel image is created.

4-Channel Raw Composite of Sony F-828 IR Image

 

 

 

As before, the 4-channel image can be given a relatively normal appearance by inverting it.

Inverted 4-Channel Raw Composite

 

[Andrea B.]

yeah, boring, i know. might be useful someday to somebody. La!!!