Lighting Research Results

Do you think that the light you want to produce could be used by me? Since I’m not too afraid of colors because after scanning I would calibrate the camera with the LAD file again. Then I should have the colors correctly as they are on the film material.

Well it will simply be a tightly spaced led ring, with some driver circuitry and a microcontroller. So in my case at least three channels for R G and B that I can trigger for a given pulse duration. This is to be used in an integrating sphere spaced for 8mm film. I expect that 35mm would require a larger sphere and thus a larger led ring.

@don007 I would be very interested to see details of a camera that has captured all the dark details of the film, whilst still giving a good balanced exposure. Pretty much every scan you see of movie film has blown out highlights or lost detail in the shadows, relative to the original film - the only exceptions being scenes with low contrast in the first place. Not saying it’s impossible, but I’m somewhat sceptical :smile:

In my experience no digital imaging camera has that kind of latitude, hence the need for HDR.

Well, I can confirm this statement from my experience too (experience: for once, I designed a real-time 3D camera which could operate reliably in dark tunnels, seeing dark-clothed pedestrians right besides bright car headlights, and in another life, I did research extensively the human visual system).

Specifically, there is no single camera known to me which can record, either in raw or otherwise, the tremendous dynamic range a Kodachrome 40 film can display. This film stock was ment to be projected, and the human visual system can easily cope with the large dynamic range a projected Kodachrome 40 image has.

A camera chip with currently 12-14 bpp per color channel can barely cope with that (quantization errors and noise will kick in) - therefore, if you want to record all the information available in the film stock, you will have to take multiple exposures. This in itself is however not “HDR”, by the way.

HDR in the technical sense is the combination of several exposures into a single radiance image. This involves the estimation of the gain curves of the camera/image processing pipeline used. Once you have these gain curves, you basically can recover from the set of differently exposed images the radiances of the scene. This HDR image is however just that - a map of the scene radiances and thus usually an image you will not be pleased to view.

These images look rather dull. This is mainly because the images we are used to have some S-shaped transfer curve applied to them, crushing shadows and highlights, enhancing the contrast in intermediate tone regions.

So an essential second step of HDR-image processing is a tone-mapping step, which transfers the raw HDR-image into something we are used to view.

This is basically also the case when you are working with camera raw images - only that you have a much reduced dynamic range in the case of raw images, compared to a real HDR.

However, the optimal tone-mapping is very much scene-dependent, and I am not aware of any single tone-mapping algorithm which would be broadly applicable.

The tone-mapping step with HDR/raw camera images is also necessary for another reason: our normal output devices have, at least at this point in time, only 8bpp dynamic range per color channel (some even less, utilizing dithering to hide it). Given, there are real HDR-displays available since some time, but how many people own such a thing? Even if these displays hit the general market in a few years from now, I doubt that they will be a match for the old Super-8 projector gathering dust in the corner.

Summarizing, I think for the time being, nobody will be able to recreate a “real Super-8 movie experience” by currently available electronic means. This hardware is just not available.

That’s why I derived my own approach, taking 5 different exposures of a single frame, each spaced a little bit more than one EV away, and combining them via exposure fusion. You can see here some results (and more information).

The good part is that this process is fully automatic (no manual fine-tuning required) and that it recovers the full dynamic range of the Kodachrome 40 film stock.

However, in that course, the appearance of the Kodachrome 40 film is changed. The final image does not look at all like a projected image. And it does not really look like a real Kodachrome 40 image either, I must confess. But I think that is the price one has to pay when working with current technology.

Note that the final output of my pipeline is not a HDR in the strict sense - the bit depth of the output image is just standard 8bpp per color channel. Since I store the original captures (which are jpeg-files, not even camera raw files), I could in principle, once HDR-displays and -video formats become widely available, rerun the pipeline and create real HDR imagery from the captures. But I guess I will never do this, as it would involve again manual interaction during the tone-mapping step.

Well, in closing, I think I need to remark that professional movie material is usually a different beast to consider. Here, the light situation is normally carefully controlled, with substantially less dynamic range used in any frame than in the average Super-8 vacation movie. I can imagine that in this case high-quality cameras and a processing path based on raw camera data can yield good results - certainly, if the scan is made from the original negative film stock.

But scanning hobby-grade color-reversal film with a single exposure per frame, recovering all the details in the shadows without blowing the highlights, when under-exposed sections directly follow some over-exposed sections? I’d be interested if someone is able to show me how to do this. :wink:

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This is a great conversation. Thanks to all who have added their knowledge. I would love to see these approaches in the Kinograph software one day as capture modes. cpixip mode = 5 exposures + a post processing step that automatically gets run at the end. Dare to dream.

This information is is mindblowing i never considerd this, i have alot of 8mm film that have exstreamly high brightnes whit very dark shadows, i never considerd that there could be a way to save the information and still make an image worth watching that was not to bright or to dark… thank you all :slight_smile:
Amazing.

… ok, trying to solve my own challenge…

I used my Raspi HQCam and my setup to capture actually image data of my standard Kodachrome 40 film stock to see how far I can push this. The Raspi HQCam features a 12-bit ADC, which is average performance nowadays. Some cameras can go up higher with raw capture, but I do not have any available.

When doing raw captures, it becomes immediately clear that only if the exposure is spot on, you are going to get good results. For capturing most of the shadow details, you want an exposure as high as possible. However, even the slightest variation in the original camera exposure will push the highlights “over the edge”, which results in loss in image quality. I will come back to this latter.

The HQCam I used has a modified IR-filter, which results in equal gains for the red and blue color channel - the original HQCam would require the red channel to be pushed (multiplied) during raw exposure by nearly a factor of two, in comparision.

Anyway, here’s the inital result of a raw capture of a single Super-8 frame:

This frame is in sRGB, with blacklevel subtracted, whitebalance and ccm-Matrix applied.

The exposure was set in a way to capture most of the dynamic range of the film stock. Specifically, the raw intensities of the little vase in the shadow, bottom-right of the frame, measure red: 274, green1: 280, green2: 274 and blue:270. This is very close to the blacklevel of the camera, which is around 256 or so. Similar values can be measured in the black frame border, with red:260 green1: 259, green2: 264 and blue: 261.

The brighest image parts are in the white vases in the background, there we find red: 2489, green1:3585, green2: 3502 and blue:1992. Remembering that the maximum value the camera can output is only 2^12 = 4096, so the exposure was spot on. In fact, the purple sprocket hole is over-exposed; the purple “look” being a common feature of raw camera captures saturating (if not taken into account by proper highlight processing, which I switched off here on purpose, to make that point).

Now this or a similar image would probably be the base for further image refinement in raw processing, basically by manually optimizing the tone-mapping of this image.

Now, comparing that to the direct output of the exposure fusion algorithm (composed of 5 captures spaced 1 EV apart),

we see that there is a notable difference in appearance. To make a better comparison possible, I transformed the (too dark) sRGB-image above to the same tonal levels as the exposure fusion result. By this, I wanted to mimic the manual “raw development” (which I am too lazy to do). Here’s the result:

Now the differences are only very mute, I must confess. So indeed, if you are working carefully, you can capture with a single raw frame the dynamic range of Kodachrome 40 film stock.

To enumerate some of the differences:

  • the exposure fusion result is less sharp than the raw result. This is a result of the extensive image processing necessary for exposure fusion. Also, the limited fidelity of the MJPEGs I am working with kicks in here.
  • there is a slight tendency of the exposure fusion algorithm to blow out bright image spots into very dark areas, visible very close to the sprocket borders of the frame.
  • the local contrast of the exposure fusion frame as well as the color definition is sligthly better than the raw result. This is especially noticable in the far distance and in the darker shadows of the image.

As promised above, I am now coming back to the issue of accidental over-exposure. Here’s the result of a slight overexposure during raw capture:

Note how the vases in the background immediately are loosing their details (and turn a little bit purple as well). If we look at one of the green raw channels,

we immediately see where the problem comes from: the green channels (pictured here is the green1-channel, but the other green channel looks the same) certainly clip in the highlight regions of the vases.

In the course of my development, I did actually consider using raw image files, but the frame rates you can achieve with raw captures were low at the time I tried this and the sensors I had available did only deliver 10 bit at most. While the last point has improved, still today, the amount of data you need to transfer and store is large, and the results are very sensitive to the perfect exposure.

I settled for taking several different exposures as MJPEG(!), which gives me the fastest frame rates for any camera sensor, moderate file sizes and in turn sufficiently fast transfer rates (my captures are transfered via LAN). To arrive at the final scan result, I combine them via exposure fusion.

The results obtained turned out to be fine; exposure fusion gives you also a process which is able to tolerate mildly under-exposed content, and important point in my application. With raw captures, the safety margin is much lower.

Exposure fusion has some drawbacks. You have to accept a slightly reduced image quality in terms of sharpness and, depending on the MJPEG-encoder of the camera, an increased noise level in the final image. The different exposures also need to be aligned perfectly, otherwise the results are not usable - this puts some strong requirements on the film advance mechanism or (in my case) on the post-processing software.

Exposure fusion is also a rather time-consuming (while mostly automatic) process. For a frame size of 1200x900, my rather fast PC needs about a second per frame (I am using my own routines, not the ones available in opencv - they might be faster). This processing time needs to be added to the scan time, which is in my setup between 45 min to one hour for a minute of 18fps film stock. So it’s a rather slow process of digitizing movie material… :sunglasses:

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Do you controle the exposures whit camra or whit light? if you do it whit the light what do you use to controle the light source?

… - I can and do both.

However, during actual scanning, exposure is just controlled by the LED-source, which is driven by 12bit DACs (an old schematic can be found here).

The camera is just too slow to respond to sudden changes in exposure time. The LED-source reacts immediately.

The different exposure settings of the LED-source were independently calibrated to have identical whitebalances. The reason is that the intensity-current curves of the red, green and blue LEDs used in the lightsource are different. So they react differently with changing current. Furthermore, the wavelength of a LED changes sligthly with varying temperature/driving current.

I am not sure that this technique of changing exposure via the lightsource would work well with pure white-light LEDs, as you would loose the possibility of aligning the color temperature for the different exposure settings/driving current. But I have not looked into that.

Only during experiments I do vary the exposure time of the camera. During scanning, the exposure time is fixed to something like 1/32-1/25 seconds. Small adjustments of analog gain and digital gain are used make sure that the internal sprocket area, where full intensity of the lightsource is visible, is imaged in the darkest exposure to values not larger than 240-250 (in the 8bpp MJPEG). Thus, the exposure is set by reference to the lightsource, not the film. This ensures that the full tonal range of the film can be captured.

Hi to all. First, I would like to apologize to everyone about the English language (I use google translator) so that I do not understand everything. Maybe I wrote something wrong that I’m sorry about, but I’d like to send you my work. I think that there is absolutely everything about details in dark scenes, the only thing that worries me is the noise of the camera. Of course, I would limit the HDR, but unfortunately I do not have a camera that could scan 2 exposures at 24 fps in real time. I would like to show you but the only way is via Skype :frowning: I speak better than I write :slight_smile: I’m posting on the forum a link to a movie trailer I did. I would like to know your opinion. Thank you all very much.

https://mega.nz/file/fL5BzKzR#41OFALJ1UVOhzqb5XbG5yeVyID1omZs7SzgU81gYPBg

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(Hey cpixp, there is some rambling here but there is a question at the very end i would really love you to answered)

I’m am always amazed by other peoples expertise :slight_smile: it kind of seem like magic, I’m a mechanical minded individual while i have a background in automation and a fair understanding of electronics, lightning and photography go right over my head, so indulge me if i loose track of reality for a moment :stuck_out_tongue:

My set up will use stepper motors to drive the film, I’m using a Panasonic G8 to shoot the frames individually, originally i had intended to take 2 shots, one IR (to use and an IR mask to clean up dust and scratches) and a white light one, but after seeing what you have done I really want to use the idea of HDR, allot of the important film I have really poor exposure, either really dark or really bright, I had always assumed this could not be corrected for because to much exposure and white out to little and shadows are black holes.

However, because of the trade off my machine took early on I’m building a small form factor I do not have much room for advanced lighting.

I would prefer to use a single source white light at 4000k (I’m assuming that cold white light would be preferable)

Now would it be possible to use the Camera shutter using cameras external remote I/O hocked upp the Adriano to control the speed of the shutter for exposure, would this control be accurate enough to control the exposure.

If do you think it would be better to simply dim / brighten the light and would that get the same effect, or would the alteration of the light change the property of the light itself not just the brightness

Hey MrCapri,

I do not have a lot of expertise with consumer grade digital cameras, so the feedback I can give is rather modest.

A lot of people have used these types of cameras to digitize film, with some very good results - even by taking just a single capture per frame. For certain cameras there exists interface software which makes controlling them from a PC presumably rather straightforward.

I have never tried this route of using standard digital cameras because I could not figure out how to interface my existing cameras to the small Super-8 frame format. And I didn’t want to buy an extra camera for my film project.

Usually, these kind of cameras are rather slow in photomode. So some people use these cameras in videomode, but I am uncertain whether you can change exposure settings fast enough in this mode to be usable. That is actually a common problem with all cameras - you have a noticable delay from the time you are requesting a certain exposure to the time the camera actually has settled to this exposure.

In fact, I switched at one point from taking images with different exposure times to working with a fixed exposure time in the camera and realizing the different exposures needed for my technique with a adjustable light source. This improved the time for scanning a film noticably.

Exposure fusion of several differently exposed images is a more involved technique than simply taking a single image per frame. As shown above, you can get very similar results both way. I would suggest an evolutionary approach, starting with the simplest setup (a constant, bright light source with daylight characteristics and a good camera) and do some scans with your material. Most of the film scanners nowadays operate like this and good results are obtained this way.

Only if you are not satisfied with these results, I would incremently advance the setup. The specific way to do that depends to a large extend on your taste and the willingness to invest personal time and other things.

One big disadvantage of taking several images of a frame is the increased scanning time. The longest Super-8 film I have has a running time of 1.5 hours - this will take my scanner about 90 hours to digitize, or nearly 4 days. Of course, the scanner can run unattended, but occasionally I prefer to check if the machine hasn’t chewed up my film.

In addition, the exposure fusion is an expensive algorithm in terms of processing times as well. For 1200 x 900 px (my usual choice) it takes about 1 sec per frame, for the maximal resolution I am working with, currently 2880 x 2160 pixel, my not-so-slow-PC needs about 3.5 seconds per frame - so for the above mentioned 1.5 hour long film, you have to add an additional 4 days to finally get the digitized frames. If you reduce the number of exposures you use per frame, the times quoted reduce noticably. Even only 2 different exposures will get you somewhere.

If you are working with raw image captures, you would not even need to use exposure fusion at all, especially if your camera features 12bit or, even better, 14bit DAC-resolution. This is all a question of taste and priorities - where do you want to spend time and effort, what is the final end product (for me, it’s web content which I can share easily) and what kind of software/workflow you have at your disposal.

While I have not tried to use a white light source, I think the shift in color temperature is not too pronounced, especially if the LEDs are ment to be dimmable anyway. Furthermore, exposure fusion has the tendency of covering up small differences between the different exposures of a single frame. So yes, that would be my approach to try out, especially because it is much easier to control. Even an Ardunio can handle that fine (in my scanner, an Arduino Nano is driving the steppers, reading the tension sensors and adjusting the LED intensities. The Arduino gets its commands from a Raspberry Pi, which is handling the image captures, streaming the images and additional data to a PC which finally stores the images and metadata on a hard disk. That setup has some historical reasons; the bottleneck is the transfer of the images from the Raspberry Pi to the PC via LAN.)

Concerning the IR image to mask dust and scratches - it will be interesting to see how far one can push this. Personally, I simply clean the film before I scan it. And many scratches you can “hide” by using a very diffuse illumination source, specifically an integrating sphere. One point overlooked here quite often is that this only works as intended if the film is as close as possible to the output port of the sphere. Otherwise, this effect is much reduced.

First off, thanks you for responding whit all this information.

It’s given me a bit to think about, in regards to not needing exposure fusion if I’m working whit raw, I’m not sure what you mean like I said this is stuff I’m very basic whit how to work whit this stuff.

As for workflow, I have no super 8 film longer then at most 15 minutes long and my last attempts at scanning threw my flatbed where I could scan 30mm each time at almost 7 minutes per scan…

I did not scan many films, I don’t mind putting in the time as long as it works.

I got a Panasonic g80 on the cheap it’s a great camera and ones a stumbled across the idea of shooting whit a reverser ring i lost my mind for a moment at the revelation and then i stumbled across this forum and i was off to the races.

The information i have got here have made me constantly reevaluated my design and my thinking.

But what you showed me whit the “exposure fusion” completely changed everything, because some 8mm film I have, it’s shot in either VERY bright daytime, or at night causing a lot of problem. Getting much information out at a single amount of exposure.

I would apriciate any more information on who you controle the dimming of the LED’s i saw the Diagram you had of the 12 bit dac controler, but do you have any more in detail on how it’s connected up to the aurdino or the LED’s?

I got digital ice built in to my flatbed scanner and it’s noting short of magical, in my case it’s experimental and i’m not counting on it being able to work but i’m going to give it a try.

Thanks very much for everything.

Well, the DAC, an MCP4812 (10bit) shown in the schematics as well as the MCP4822 (12bit) I am currently using have an SPI-interface (marked SCK and SDI in the schematics). Any Arduino has some of its input/output-pins dedicated to a specific function. Specifically, with the Arduino Nano, the pin D13=SCK, the pin D11 = MOSI and the pin D10 = SS is of interest here. Have a look at this page for some further reference.

Normally, in the Arduino world, you connect an external IC either directly, via I2C or SPI. For a specific device, you also need a library in order to talk to the different registers of an IC for example. Usually, you are lucky and someone already did write an Arduino library. Than it’s easy sailing. You can find numerous examples at these pages here and otherwise.

Well, to illustrate the schematics a little bit in more detail: the MCP48?? gets a register set to a value between 0 to 4096 (12 bit version) or 0 to 2048 (10 bit version). This causes the DAC to output a certain voltage on its pin 8. This voltage is piped to the input of the operational amplifier (U1A)

This unit is trying to keep its inputs 2 & 3 at the same voltage; it can only do this by opening more or less the IRF1010N (Q2) so that over the resistor R8 a sufficient voltage drop occurs. The current flows from the +9V via the connector J1, where the LED is connected, through transistor Q2 and resistor R8 to ground. That circuit is a simple voltage-to-current converter. C4 and R6 are a simplistic low-pass filter to avoid that the operational amplifier starts oscillating. As I mentioned earlier, a crude design with parts I found in my part bin. You can probably find better designs for programmable current sources on the internet.

One important point: there are basically two ways to dim a LED. The one used in dimmable LED-strips for example is PWM - pulse width modulation -, where high frequency constant current pulses are driving through the LED. The light intensity is controlled by varying the width of the pulses. That is a simple, cheap design - stay away from it for scanning purposes. You invite all kinds of trouble.

The design sketched above works by actually changing the current through the LED continously - this is more involved and more expensive. Mainly because you have to take care of large amounts of excess heat generated by the transistor (Q2 in the schematics) and the measuring resistor (R8). Both have to be quite beefy.

One last comment: like any analog film material, Super-8 film stock has a limited dynamic range. Material which was over-exposed during shooting too much will have burned-out highlights and there is no way to recover that lost information. On the other end of the scale, severely under-exposed material will show very little structure in dark shadows, with a lot of noise. This is also very difficult to recover, and at a certain point, everything will be just a structureless dark noise blob. However, if you can see structure in the highlights and shadows in a normal projection, chances are that you will be able to recover this electronically.

@MrCapri, if you can integrate a Raspberry Pi into your build, you might want to check out gPhoto2 for controlling your camera. This allows you to control most DSLR and DSLM type cameras programatically from a Linux machine (the Pi included). Depending on the camera you use, you can control more or less functions, but the basics (such as releasing the shutter or setting the shutter speed/aperture) work on most models. All you need in hardware is your camera’s USB cable plugged into the Pi. Just check for what functions are compatible with your camera. There is also loads of beginner’s tutorials around the internet, so you should easily be able to get started.

@cpixip, nice explanation of the circuit. I initially wanted to do my lighting setup without any current control and only use the exposure time of the camera. Since I want to use a mono camera and combine three (RGB) channels it might be good enough. But then again it is much more flexible and ‘fun’ to have some analog current control. Although I would not want to use a very large range since the color frequency will shift somewhat in the low ranges.
Here is a link link describing the effect.

@cpixip , Thank you agine, we can see struckturs and if i over expose i can see what is in the dark patches and so forth.

These films will never be perfect or even some al all recoverabul but any chanse to get anything out of them is going to be an amazing opertunity.

For exampel one film is of out of a window of a cargo plane at dawn or dusk you can see there is alot of stuff but its way to dark

@jankaiser I have looked in too gphoto2, unfortunaly the Lumix g80/g85 is not supported, while some peopel have got the shutter to work, adding a Rpi simply to run the shutter is alittle overkill, if i can get the same result from adjusting the LED brightness and that would also enable faster shutter speed to be used.

… you are absolutely right, this effect is there and I remarked above that if you are utilizing white light LEDs, you have no chance to counteract it. However, I am using separate red, green and blue LEDs, and the 5 different illumination settings are independently calibrated to the same color temperature.

There is actually another reason one has to go through such an individual calibration of every illumination setting: the current-intensity curves of the LEDs used are very different, so doubling the current on, say, the red LED is not equivalent to doubling the current of the green or blue LED. The imbalance caused by this is actually much stronger than the shift of the main peak of a LED by changing the driving current.

To give an example - the darkest illumination level I am using has the calibrated setting red = 113, green = 126 and blue = 52 (the full range spans from 0 to 4095). The brightest illumination level has the settings red = 2146, green = 4095 and blue = 889. So while the red and green components have nearly similar amplitudes at the lowest illumination level, the red component is only about one half of the green component at the highest illumination level. This is mainly caused by the different current-intensity curves of the LEDs, which are in turn caused by the different materials used for the different wavelengths.

I did actually tests where the color balance of some of the illumination levels was off (not much) - depending on the settings of the exposure fusion algorithm this was barely noticable. The reason is that exposure fusion tends to average for each pixel over several exposures. This reduces any deviation which is happening, including color shifts and image noise.

The current image capture pipeline is tuned to capturing standard Super-8 material. As I know from experiments, the Raspberry HQCam is assuming “daylight setting” in its processing pipeline (that is independent whether you use the standard one, the BroadCom stack, or the new one, the libcamera stack). So the illumination is set to deliver just that - light which mimics “daylight” as close as possible.

This actually ensures also that the raw camera channels are utilizing the maximal dynamic range possible, which was one of the goals of the design.

Setting manual whitebalance will also result in choosing a fixed ccm-matrix by the image processing pipeline while creating the MJPEG-images I am using later for exposure fusion. At this point in time, I do not know whether other steps in the image pipeline are changing colors as well (the automatic lens shading algorithm might be a candidate), but from test I would judge such influence is minor (if present at all).

I am still working on a good way to scan Super-8 material with a severe color cast, for example film which was exposed without setting the daylight filter of the camera correctly. It is possible to scan such material by changing the whitebalance settings of the camera (keeping all other settings fixed), but this approach lowers the amplitudes available in the raw camera channels, lowering in turn the dynamical range available for processing. It would be better to keep the whitebalance settings at “daylight” and adjust the light source to the material at hand - I am currently looking into whether this is possible.

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I am always suprised of the internets ability to find likeminded people, even though I grew up with it.
I plan on building a machine to scan cut still film and am researching of how to design the lightsource for the integrating sphere. Someone at labsphere recommended a sphere with a 25-30mm diameter for backlighting a 6*7 negative.
I plan on going with RGB Leds but have problems choosing a good option.
The datasheets of most multicolor chip LEDs often show relatively powerful lumen outputs for red and green, while the blue LED is often weak.
Wouldn’t a good lightsource need to provide continous lumen output throughout the spectrum?
I don’t understannd why these LEDs e.g. https://www.mouser.de/datasheet/2/228/LED_2520Engin_Datasheet_LuxiGen_LZC-03MA07_rev1.8_-1531871.pdf have such odd balancing of R,G, B (although I now that blue LEDs are more complicated in their design)
Yes, you could always gain the individual channels to match, but that would mean pulling up noise as well. Wouldn’t it be desireable to have equal lumen output for R,G,B as the quatum efficiency of monochrome sensors seem to be relatively equal.
What approx. lumen output per channel would you recommend for a sphere with a 20cm diameter?

This is the quantum efficiency of a modern mono sensor:
BFS-PGE-122S6M_624x312
And it’s color version:
BFS-PGE-122S6C_624x312
And here are the spectra of some daylight situations:

So you see the blue light wavelenght is a little bit lower (in dB), I think that is the reason of the combination. But I might be wrong!! Was also wondering what would be the best bnrightness for the blue leds’s since as you see the quantum efficiency is lower for the blue colors, and you might compensate for it.