Tuesday, January 22, 2013

The Sight of Silence II

Making quite a bit of progress with the noise reduction.

For people just tuning in: I'm talking about the next release (not here yet).

DNGMonochrome doesn't show you a 'live' result you can work on and I decided that for noise reduction that had to change. I wanted to be able to push those sliders and see the effect instantly, without having to re-interpolate the whole photo.

But in order to do that I had to cut the area that's interpolated, since speeding up the whole procedure wasn't an option: apart from technical limits, it would never be fast enough.

So I implemented a dedicated 'noise preview', which will show the preview image (after interpolating the total photo once) with a 100% crop and a 200% crop, quite similar to the main screen.

You can then navigate the preview image and select the area you want to inspect. And the selected area will be noise-reduced very quickly by re-interpolating only the selected bit and not the whole photo.

This instant feedback is really the only way, because the noise reduction options I implemented so far are quite extensive.

Before interpolation

Before interpolation you can denoise the secondary channels of the RAW file separately (e.g. when producing a regular monochrome DNG you can denoise the red channel and the blue channel before interpolation). The effect is very subtle and you really have to look for it, but especially in the shadow areas it's quite noticeable.

When interpolating with the RAW red filter or the RAW blue filter, these 'before interpolation' sliders work on the green and blue channel and on the green and red channel respectively. Here the effect is a bit stronger, because the green channel is more dominant and occupies 50% of the sensor.

The main channel is untouched, because for that one it makes more sense to reduce noise after interpolation, since the before and after values are the same, e.g.: when interpolating the regular monochrome, the green pixel values don't change. Also, the effect of reducing noise in the main channel before interpolation leads to very strong and unsatisfactory results: too much detail gets lost.

After interpolation

And then there's three sliders for the 'after interpolation' results. They work on the final result, where noise reduction is applied on the DNG after it is reduced to one monochrome channel. These sliders also work on the RGB filters, where noise reduction is applied to the separate results before they are mixed.

Both the before and after interpolation have a detail slider, which works (in effect) quite similar to the Lightroom detail slider.

Here's a preliminary screenshot of the noise preview window.

Note that the final result in the next release might (and most likely will) look different. It's not finished yet. Also, I was a bit apprehensive about the 200% preview, since the upscaling algorithm is out of my hands. For quality you have to concentrate on the 100% view. The 200% will give you a good 'noise' indication, but it will also show jagged edges - due to the upscaling - and an overall fuzzy image.

Despite all these noise reduction options, my advice would still be to use the Lightroom noise reduction (or any other RAW converter you might be using) for the final result if possible (e.g. when converting to regular monochrome).

I think the 'before interpolation' sliders are very useful for all conversions, and when you're using the RGB filters you should use the noise reduction for the red and blue result, but otherwise I would leave it up to your regular RAW converter.

Not that there's anything wrong with the present implementation, but in a practical sense: DNGMonochrome doesn't remember the position of the sliders per photo. If you want to 'redo' the DNG conversion to monochrome, you have to start all over again. In that sense it's best to limit the use of these options within DNGMonochrome as much as possible.

For the RGB filters however, Lightroom isn't a good alternative. Once you start mixing the red and/or blue result for filtering, Lightroom can only partly help you out if the red or blue channel turns out too noisy. You have to tackle that noise in DNGMonochrome first, before you create the final monochrome DNG. And that was also the main reason for this extensive noise reduction implementation.

As mentioned before: I hope to have all this - and some other new stuff - finished somewhere in February...

1 comment:

  1. very interesting anticipation, I'm eager to look your next working release - and many thanks for sharing this very interesting software as freware - ciao from Italy