Issue I: On Highlights Of The Blown Out Kind

It wasn't just noise reduction I've been working on... because there's a few other issues I like to resolve...


On highlights of the blown out kind

First of all, if you read some of the reviews of say the Leica M Monochrom, you'll notice that users discover that highlights get blown very easily.

Funny thing, DNGMonochrome does exactly the same: highlights that still give detail in Lightroom after B&W conversion are sometimes completely lost after conversion to monochrome with DNGMonochrome.

Here's a crop... a really tiny piece, perhaps 5%, from a Canon, with the highlights toned down a bit... nothing done about it otherwise... loaded into Lightroom without sharpening or noise reduction, then clicked on black & white... notice the detail at the top of the windows, in the glass (actually behind the glass).

Lightroom turned black & white...

Now look at the monochrome version with the same toned down highlights... it's all gone...

DNGMonochrome turned monochrome...

Apart from the clarity and sharpness of the monochrome version - also no sharpening or noise reduction on these monochrome crops - Lightroom clearly wins in the details... With a bit of work on that one I wouldn't be surprised if you preferred the Lightroom one, seeing how DNGMonochrome lets you down on those blown highlights.

And bringing down those highlights on the monochrome DNG in Lightroom really doesn't work. That only turns everything gray.

No, those monochrome windows are a lost cause... well... perhaps...


Lightroom can...

But why is it that Lightroom can and DNGMonochrome can't?

Well, this one isn't because I'm not Adobe...

No, it's quite simple really: if the monochrome file is blown, so is the color file... except... in the color file in a lot of cases it's only the green channel (the pixels registering luminance) that's blown, since the blue channel and especially the red channel get filtered much stronger and register lower values most of the time.

Hence, if you interpolate directly on luminance (the green pixels), as DNGMonochrome does, or if you shoot with a camera that only registers luminance, you lose that blown out detail.

In this particular color file, the green channel is blown, but the blue and red channels aren't, at least not on that detail behind the glass.

From a purist view: you could say that DNGMonochrome gives you the true experience :-)

If you color interpolate, you only have to lower the luminance portion of the blown bit to get your detail back, which then consists mainly of the information from the red and the blue channel. In fact, the simple procedure - during color interpolation - of mixing the three values can already be enough to recover detail if blue and red aren't too high: the influence of the green pixel is diluted. It even works when two channels are blown out. Detail recovery still possible through the third channel. Usually not the nicest, but possible.

So, people trading their color camera for a B&W only camera, suddenly discover the benefits of the Bayer filter when it comes to this issue, especially if they weren't really aware of this when shooting with the color camera. Their RAW converter saved them most of the time.

In an all B&W camera without Bayer filter nothing can be done about this. Perhaps patch the blown out part a bit in Photoshop, but the original detail is lost.

But in DNGMonochrome that's unnecessary, because the information from the blue and red channel is still around.

There's no need to let that detail go to waste.

So, enter the highlight recovery option... and then you get this...

DNGMonochrome turned monochrome with highlight recovery, bringing back the details at the top of the windows...

It's still in quite the experimental stage, because getting this right isn't easy, but it's one of the things I'm experimenting with and working on.

The big problem is that this works best if it's applied locally, but DNGMonochrome isn't set up for that. It's not difficult to apply these corrections to only a certain part of the photo - after say selecting the top of the window - but that selection isn't stored with the original. If you want to redo the photo you have to start all over.

So first I want to see if I can get this right for the whole photo.

Then another issue - be it less complicated - is that what seems blown out in the preview of DNGMonochrome might actually not be, when you load the DNG into Lightroom. So I need some way of detecting - and letting you know - when you should apply it and when not.

And yes, for parts of the photo this is actually cheating. When using this proposed option, DNGMonochrome will divert from the strict 'luminance only' approach... but only for the blown bits.

Actually DNGMonochrome already has the ability to partially recover blown highlights: the RGB filters. If you mix in a little bit of blue or red (try 5% or 10%) - depending on which channel gives you the most detail back (check via the RAW filters) - you most likely can get some of your detail back. But then you might alter other aspects of the photo you didn't want altered.

So, I hope to get this presentable enough for a next release, but currently I don't want to make any solid promises on this issue (I haven't shown you the ghastly effects this option can also produce when out of control).

Next time I'll talk about another issue I hope to get solved for the next release...