Quattro and the blue channel trick revisited


There is hardly a photographer who shoots with a Sigma camera who doesn’t know about the blue channel trick. Those, who have never heard about it, should read this blog post of mine. The tl;dr version is this: it’s a workflow trick for black and white conversion, with which you can improve the noise performance of the Foveon sensor immensely. Sounds awesome, what’s the problem? Well, this trick, which made a huge difference with cameras with the Merrill sensor, no longer worked with Quattro cameras upon last and all previous examinations. Since then, however, two and a half years have gone by and several new Sigma Photo Pro versions have been released, which makes it possible that the blue channel trick was secretly reintroduced, without me or other photo bloggers noticing it.

With blog posts such as this one, where I discuss SPP and photo editing, I usually start with the context. I’m sure, that for you readers it is important to understand the workflow and especially the settings used, so that you can reproduce the results.

  • For this post I have edited 3 photos in 4 different ways in SPP‘s monochrome mode. In each of the crops you can see the letters RGB, R, G or B. These correspond to settings in the color mixer tool in the monochrome mode. The “point” was therefore set in the middle of the circle (=RGB), at 100% red (=R), 100% green (=G) or 100% blue (=B). This is the best way to determine whether the use of information from different color channels has any effect on luminance noise.
  • In order to ensure comparability all the remaining settings remained unchanged.
  • These photo were shot with a Sigma sd Quattro.
  • If you would like to do some pixel peeping, you can find all the 12 photos in full resolution on Flickr. 🙂

Here are now the 3 uncropped photos and the 12 crops.

Conclusion:

As you can see, nothing’s changed. The Quattro sensor is still unable to take advantage of the sole use of information in the blue channel. The reason for this remains a mystery. One reader wrote in the comments of one of my previous posts that the blue channel trick is maybe already being used automatically with the Quattros, which is why clicking on 100% blue in the color circle changes nothing in regard to luminance noise.

 

  1. Hi Lars, Unlike the original Foveon chip, the red and green layers of the Quattro chip are only one quarter of the resolution of the blue layer. So it has to be that the blue layer data is being used to supply the luminance of not just the blue channel but also the red and green channels. This is why you see no difference between channels in these tests, you are already getting the best of the blue channel across them all. Well, that’s my theory anyway! 😉

    Reply

    1. Hi Tim, your theory sounds convincing. I was hoping, however, that Sigma could come up with some magic sauce that would make it possible to improve the output further. 🙂

      Reply

  2. Hi Lars, I do the Blue Channel Trick with Quattro by using RawDigger to open the X3F file then exporting to 16-bit TIFF the top layer, labelled ‘B’.

    With my dp Quattro it works perfectly. With sd Quattro the image will contain the PDAF pixels, which would need some cloning in post processing. It would be easy to create a Lightroom preset to apply this correction in one click.

    Having said all that, I personally prefer my results using SPP Monochrome with Quattro files.

    Regards

    Reply

    1. “Having said all that, I personally prefer my results using SPP Monochrome with Quattro files.”

      I didn’t experiment with RawDigger with sd Quattro X3Fs, but I did with DP Quattros. And my conclusion was similar to yours. I prefered my results using SPP. Plus it was more work with RawDigger and it’s even more still with having to have to clone he PDAF pixels with the sd Quattro files. I will stick to SPP. 🙂

      Reply

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