Fuji's 4th color layer

[Tim Gray]

I have a couple questions about Fuji's 4th color layer. This layer is cyan sensitive, presumably centered on the 'green spike' emitted by fluorescent lights. As I understand it, this effectively creates a mask proportional to this color, providing more natural color under fluorescent lighting.

My questions are:

1) Doesn't this harm color fidelity near this wavelength of light? If you took a picture of something of this color, doesn't the 4th layer work against you?

2) All the literature I've read about it says it's effective in fluorescent and 'mixed lighting'. I take 'mixed lighting' to mean combinations of fluorescent, metal halide, and other non-ideal light sources and daylight. Online in forums, it's often presented as tungsten + daylight. I can see the former, but not the latter. For the latter to be true, we'd need variable sensitivity to blue light, right? This often comes up in discussions of Portra 800 and Fuji 800z, as if 800z some how magically deals with tungsten light better. Of course, I'm not questioning it's ability to handle fluorescents in a way that the Portra does not.

I shot some Reala 500D in 16mm, which incorporates this 4th color layer, and it does do a great job of dealing with fluorescents. There's no denying that.

 

[RPC]

I shot some Reala 500D in 16mm, which incorporates this 4th color layer, and it does do a great job of dealing with fluorescents. There's no denying that.

When I tried some of the original Reala, the first film with the 4th layer, I found it seemed to produce better skin tones in the shade without flash than other films. Has anybody else experienced this with that film or any of the current 4th layer films?

 

[pentaxuser]

Not an answer to the OP just more questions so sorry about that. I noted some time back that Fuji used to advertise its Superia emphasisng the fourth layer then it seemed that this was dropped. It was on every box of Superia for a while but not on every Fuji colour film.

So does all Fuji colour neg film have the 4th layer now and if not which don't have it and why not?

Have other films such as Kodak caught up and now use 4th layer? If not then why not if this 4th layer is a clear advantage?

I am confused and am left wondering if the 4th layer is marketing hype or a clear benefit.

pentaxuser

 

[hrst]

pentaxuser,

I remember this was pondered here a while ago.

I remember the consensus being, at least how I thought back then, simple;

Fourth layer had a task of helping color rendition in a specific lighting conditions. As it wouldn't make any sense for Fuji to worsen their products, it is very probable that they have invented a new way to reach the same goal without the fourth dye layer; probably a better one. It may be a new sensitization dye in the green-sensitive layer or something like that. Wouldn't that make sense? Removing that extra layer would provide a minor advancement in resolution, as well as cost reductions in coating.

At the same time, the resolution of these films got better IIRC.

 

[Tim Gray]

It's still an interesting technology. When I shot the 500D, we also shot some of Kodak's Vision3 500T, and that made a green mess of fluoro's. However, I would imagine it has to have a trade off...

 

[keithwms]

1) Doesn't this harm color fidelity near this wavelength of light? If you took a picture of something of this color, doesn't the 4th layer work against you?

No, because the mercury lines are so sharp.

When you look at the sensitivity curves of all the layers in a conventional film without a 4th layer, I think you'll see that there are some dips between blue and green and between green and red. The fourth layer simply fills that dip in the blue-green region. If the sensitivity curve is smoother in that region, then the individual colours there will be better distinguished. So then you have a better shot at isolating a specific colour e.g. with a filter.

Again, note that the spikes that matter most, the blue one at ~438 nm, the green one at ~546, and the pair at 577 and 579 are so sharp that it's pretty easy to isolate them without affecting the adjacent wavelengths... as long as the sensitivity is smooth across those regions.

2) All the literature I've read about it says it's effective in fluorescent and 'mixed lighting'. I take 'mixed lighting' to mean combinations of fluorescent, metal halide, and other non-ideal light sources and daylight. Online in forums, it's often presented as tungsten + daylight. I can see the former, but not the latter. For the latter to be true, we'd need variable sensitivity to blue light, right? This often comes up in discussions of Portra 800 and Fuji 800z, as if 800z some how magically deals with tungsten light better. Of course, I'm not questioning it's ability to handle fluorescents in a way that the Portra does not.

Again I think the main issue is that you have good smooth sensitivity across the board. By that I mean, you don't want a sensitivity curve that is at all bumpy from blue through red. Bumps in the colour sensitivity curve imply large changes in density over a small change in wavelength.... hence a spikey lamp spectrum can be problematic, even if the subject looks good to our eyes under that spikey lamp light. So... ideally I think you want a perfectly flat sensitivity curve, which gives equal weight to all the colours.

Incidentally, my recollection is that Fuji did not develop 4th layer to try to deal with fluorescents or mixed light- they were simply aiming for smoother colour transitions. I recall that they admit this somewhere on their website.

 

[Tim Gray]

This makes sense. Smoother spectral sensitivity.

That might have been the original reason Fuji developed it, but in their spec sheets, they also mention the lighting thing.

Presumably Kodak thought there was a better way?

 

[keithwms]

Well I am not going to answer that and start a speculative brand war :rolleyes:

Anyway, here is some more info....

This technology was initially designed to help render colors more accurately, but an unexpected and very useful side effect is the 4th layer's ability to remove much of the "green spike" that results when un-corrected fluorescent and sodium lights are mixed with daylight-balanced sources.

..from this site.

 

[Tim Gray]

Haha, of course not. Hoping to hear PE's take on it. It is interesting that Fuji is doing away with it in some of their films.

 

[brucemuir]

I only have limited RA4 printing experience but so far I've noticed that Fuji is easier to print when using a daylight film under tungsten.
My family room also has a sickly yellow ceiling and I bounce electronic flash off it alot and this seems easier to correct.

I've been shooting alot of 160s & 400H and comparing against the Portra NC lines.

Anyone else notice how fuji handles tungsten?

 

[Tim Gray]

RE: the tungsten bit - I've found that Porta shot with no filter handles tungsten lighting very well. Of course I was adjusting in Photoshop or had it done for me at the lab, so it might be different with RA4, but my corrections were nothing complicated.

I'm playing around a bit with the spectral sensitivity charts of Kodak Portra 400NC and Fuji 400H. I scraped the data from the charts in the spec sheets, replotted them, and also plotted the 'color blind' sensitivity gotten from summing the individual RGB (and cyan) components. I'm guessing one might need to convolve this with the spectral dye sensitivity curves to get a more final result in terms of what ends up in a print, but 400NC and 400H have very similar curves here. Anyway, I'm more curious about the sensitivity of the film.

I'm ignoring irregularities in the sum which arise from where the data for each component ends (I set it to zero where no data exists). Regardless, I do notice two differences, other than the obvious addition of the cyan layer. First, Kodak's red and green layers clearly extend to shorter wavelengths than Fuji's, by a significant amount. Take a look at the green curve specifically. Secondly, the Kodak curve actually looks flatter, even though the cyan layer does make a noticeable difference in the Fuji film. I'm not trying to discount the Fuji's performance - it clearly handles the green cast of fluoro's better.

I'm adding the sensitivities, not the log sensitivities by the way, so 10^(log sensitivity). I think this is the correct way to do it, but I've been wrong before. If this is in fact wrong, I get a vastly different result. I'll post the graphs if this sounds like a valid analysis to you guys

 

[Photo Engineer]

There has been some debate on and off about whether this 4th layer is present or not. Some have noted here that Fuji stopped using it. Their data sheets on their web site do show that the 4th layer is there and has peak sensitivity at about 510 nanometers. It is called the cyan sensitive layer. It is very slow in speed compared to the other 3 major sensitivities.

Evidence also suggests that its use in some films degrades the results when cross processed. I have no data to support this except those posts on APUG which mention that Fuji films cross process rather poorly.

It is said to render colors more faithfully under fluorescent lighting. They are also using an inverted layer structure to improve grain and sharpness. This was first patented by EK and is now being used by Fuji. EK never used the 4th layer.

PE

 

[Tim Gray]

Upon further reading, I see where some of my initial confusion came from. I was reading on a cinematography site where the description of the 4th color said that the layer created a 'traveling suppression matte of the green spike.' After the discussion here, and a perusal of the spec sheets, I think this is incorrect.

 

[keithwms]

Tim, will you show us your plots? Sounds interesting.

Ron, I wonder how the 4th layer might affect magenta sensitivity.

 

[2F/2F]

...as if 800z some how magically deals with tungsten light better.

It ain't magic, but if you remove the words "magically," and "as if." the statement is true IME. Fuji films do correct more easily and accurately from being shot in tungsten illumination than do Portra ones; even when underexposed. I love Portra, but I use Fuji if shooting in anything very far away from 5,000 K.

 

[Photo Engineer]

Tim, will you show us your plots? Sounds interesting.

Ron, I wonder how the 4th layer might affect magenta sensitivity.

Keith;

That sensitizing dye would be reddish in color given the ~510 peak. I don't see it as causing any problem.

PE

 

[Tim Gray]

Sure thing. I've attached them. Portra 400NC is first, followed by Fuji 400H. The colors should be self-explanatory; the black line is the sum. I'm sure it's more complicated than I treated it though.

The spec sheets show the sensitivity of the cyan layer. In the cross section of the film it calls it a 'light magenta image' layer after development. I did a little searching on patents and found this. Unfortunately, the Reala patent that is referred to is in Japanese as far as I can tell. They do talk quite a bit about cyan sensitive layers with IR dye couplers and/or DIR compounds to promote interlayer effects. I don't understand enough of the photo science to get what's going on though.

 

[Tim Gray]

More info from Fuji:

Human vision makes fine distinctions between shades of color. We distinguish between subtle shades of green, for example, by subtracting the red component of light. To replicate this ability in color film, we developed a green-color-correction layer that suppresses red when capturing green colors. This achieves more faithful green, blue-green and yellow-green hues.

 

[keithwms]

Hmm your plots certainly don't back up what I was saying, the Fuji curves don't look appreciably smoother. There must be more to it than I thought.

 

[Photo Engineer]

Keith;

I think that is what struck me too, but then it should have no big effect unless other things are going on. It is hard to look through the hype. But then, Kodak does the same I guess.

PE

 

[dmr]

Hype or not, I've noticed that the Fuji C41 films are more forgiving in available-light and mixed-light situations. Back a few years ago, they told me (the ubiquitous "they") that the 4th color layer was responsible for this.

 

[Photo Engineer]

I get about the same latitude from Fuji and Kodak negative films.

PE