Aerochrome color shifts SOOC with Foveon

[Christoph]

Emulating Aerochrome is a long and winding road. Anyone who has read my previous posts on Aerochrome has probably seen my frustration in achieving an authentic look. 

 

Now I am back with the Foveon (Sigma SD1 Merrill) and have tested with the Triple Bandpass. And suddenly I achieved an in-camera look that is actually not bad at all.

 

The magic phrase is FOV Classic Blue. This is an in-camera preset that exists in the Sigma SD1, like “neutral”, “landscape” and so on. What it does? I don’t know. Like much else about Sigma’s Foveon sensor cameras, it’s a black box. But in any case, it results in getting red-pink trees and green-blue skies right out of the camera with the Triple Bandpass filter from Midwest Optics.

 

The color changes were unfortunately not there yet, with the exception of yellow to white. But red was still reddish, or let’s say at least orange. But if you install an additional filter that flattens the transmission curve of green (in the 550nm range), then it becomes good. Why? I do not know.

 

The best result I got so far was with magenta/pink filters from Lee. Here are some results. Unfortunately I did not get a Custom White Balance with both filters together. That would be necessary to get a convincing result.

 

It's not perfect yet, the color changes aren't optimal yet, as well as the coloration in the vegetation, but I think that's a big step forward towards authentic Aerochrome SOOC.

[Christoph]

I can't upload images, but you can look at them on my blog: 

 

Hidden Realms | Blog

 

 

 

Editor's Note:  The upload problem has been repaired. See Christoph's post below for his photo uploads.

[colinbm]

The good 'ol days with Foveon IR, they were good.

[GaryR]

I think there will always be some contention as to what authentic digital Aerochrome is, but Foveon false colors are unique. I've had most of the Sigma dslr's over the years, but currently keeping it simple with a FS-converted DP1x and DP2s.

[Fedia]

Your results look a lot like the real thing, especially the absence of green in the water and the windows. It seems the camera has really turned green light into blue.

 

I have a full spectrum DP1s and there is no FOV classic blue fonction in it. What I have experienced is that there is no way to get a usable color image with it If you cut the blues out, meaning any filter from red to orange to yellow to green will produce uniform pink. Different types of blue filter work very good as well as IR cut filters. That's why i'm surpised at the colors you got without any blue light coming in.

 

It looks like you forced the green to blue, red to green, Ir to red shift to happen in camera. Since each foveon color channels has a very wide range of spectral sensivity, with a lot of overlap between the curves, it is technically possible for the blue channel to be sensitive to green and to the green channel to be sensitive to red.

 

You can draw a line at 550nm and 660nm and see that happening

 

You may have noticed that in full spectrum mode without any filter, red objects appear yellow or orange. To me this is due to the fact that the red channel is so stimulated by IR its gain has to be drastically reduced to match the level of the other channels, making the red curve fall under the the green one in the 630-700nm region, making the green channel more sensitive to red light than the red channel itself, thus making red light appear green and red objects (which almost all the time reflect IR as well) appear yellow.

 

Here an exemple of this with a very common exemple of monochromatic light, traffic lights.

 

 

 

 

So if it is possible to make Orange appear green, and red appear yellow-green, it might be possible to make green light appear blue. The question now is how to make the blue channel MORE sensitive to green than the green channel itself to produce the effect.

 

To make red light even more green than in full spectrum/no filter mode. It is possible to add a filter that will provoque a green channel raise in the white balance.

On the following image a blue filter that passes IR very well. Note the orange colors of the trees due to the green channel also picking IR due to the gain increase.

 

 

 

[Christoph]

I still can't upload images... will try again later. Would like to show you some images of traffic lights... The red is yellow-greenish, the green is blueish...

[Christoph]

16 hours ago, Fedia said:

So if it is possible to make Orange appear green, and red appear yellow-green, it might be possible to make green light appear blue. The question now is how to make the blue channel MORE sensitive to green than the green channel itself to produce the effect.

 

What about using the DB850 and a combination of filters from Lee that kind of produce the TB effect with peaks at green an red?

[Christoph]

Now it's working...

[Fedia]

This is amazing, you really shifted the spectral sensitivity of each channel towards longer wavelensths. This is aerochrome. The foliage is very accurate : bright red and pink for the greener/younger leaves.

 

I tried my actual filter setup (DB850 + 550nm) on my sigma. very briefly today : It gave only two color : grey and a sort of brown for what reflects IR. I didn't take pictures, just looked at the liveview. I will take proper pictures tomorrow.

 

You have the a 15M pixels sensor on your SD1 I think, I only have 5M on my DP1. It is not the same generation of sensors. So maybe that is a reason why it doesn't work.

 

So If you shoot with another picture profile and not the "FOV classic blue", does the effect happen ?

[Christoph]

It's great and strange at the same time, because it's just a damn preset. No idea what it does exactly. I tried it out of desperation, because all attempts with CMOS failed respectively didn't give the result I was looking for. So I tried again with Foveon, but only with the aim to optimize the full spectrum look or to test again with green and orange filters.

 

There is no need to change anything with the TB. These images are SOOC. I didn't do anything with the contrast, saturation etc or the strange slider on the right. The only thing I did is to optimize the coloring with this pseudo WB tool. Because with the TB you can get a White Balance, but not with additional filter. Hmm. Maybe it worked with a yellow filter, but not with the pink filter ("Middle Rose"), which has given the best result so far.

 

I had already tested the TB years ago with the SD1, but not with FOV Classic Blue, but only normally with the goal of getting a photo that would give a good result after channel swapping. Which of course it did not.

 

I will try again with another preset, but I am convinced that it gave some strange tint, even with CWB. 

[Fedia]

I didn't have time to properly test my filter combo on my DP1 otday but I brainstormed a little bit last night to and I think I'm begining to understand why the TB gives better colors.

 

I took the Foveon transmission curve I posted earlier and roughly paired It with the TB on one side and a normal yellow/orange filter on the other. I focussed on the blue channel only. Since we are trying to understand how green was succesfully recorded in the blue channel of your SD1

 

 

I hope this is not too unclear, but the conclusion I make of all this is that the green signal recorded in the bue channel is less polluted with other colors when using the TB.

 

So maybe that's the mechanism why the peaks work in enhancing the colors.

 

I wonder if the saturation would go up if we took an uncoverted camera and mounted it with a TB type filter with peaks at 440nm, 550nm and 660nm. could be. In the case of a bayer sensor there wouldn't be any overlap beetween the channels anymore. Would this produce saturation ?

 

 

 

 

[Christoph]

This is color mode "neutral", with TB and "Middle Rose":

 

[Fedia]

That's a huge difference... And that is pretty much what I get on my camera. I will post a photo later today.

 

And what does "FOV classic blue" do when the camera is used in the visible range ?

[Christoph]

I lost my SD1 hot mirror, unfortunately...

[Christoph]

Still TB with "Middle Rose"... Maybe a bit too pink for my taste... The essential really seems to be the balancing of green, red and possibly IR. Especially green so far. 

[Christoph]

This is an interesting reference that shows the color shifts of the original Aerochrome (I assume it is). Some might be familiar with this document:

Understanding Color Infrared Photography (core.ac.uk)

[Fedia]

I can recognise locations from your other photos. It's quiet different with foveon colors, they are so dense. I wouldn't say too pink but it's true full spectrum foveon colors are nearly clipping all the time.

 

That's the colors I get with The sigma DP1s and a 550nm + DB850

 

 

 

 

No variation at all and the sky is green;

[Christoph]

Yes, everything except red/pink seems to be dull, like in my TB "neutral" shot. It's so weird that a preset makes all the difference...

 

I've just looked through ebay for SD1 Merrills - their prices have gone up considerably since I bought it some years ago...

[Fedia]

What's the difference beetween the merrill and the non-merrill ?

[Christoph]

Honestly, I have no idea! Maybe someone else in the forum knows this... Maybe Foveon Blue does work with other models as well... 

[Christoph]

I was finally able to do a CWB with Middle Rose which only purpose is to lower the transmission curve of 550nm. The tone of the vegetation imrpoved a bit. Together with the Orange-16 filter, this resulted in almost optimal coloring for my taste.

[colinbm]

I really like the vegetation in the third one.

[Fedia]

Does the end credit roll now ?

[Fedia]

could you try this with the DB850 and an orange filter ? I would like to know which of the TB or the "FOV classic blue" profile is primarily responsible for the effect. Thanks.

[Christoph]

I would, but I can't because I have no DB850 available for me right now. I have one built into my Nikon, and that's the only one I have right now... Sorry!