Comparison of RAW Demosaic Algorithms: AHD, AMaZE, RCD, and Actual Image Testing

What to do with demosaic?

The photosensitive points of Bayer or X-Trans RAW each record a single channel sample after passing through the color filter array, and the RAW development software needs to form a displayable color image accordingly. This step is called demosaicing. The algorithms and options provided by different software are not the same; the algorithm name itself is not enough to predict the image quality ranking under all cameras, ISOs and patterns. 〔G-DEMO-01〕

AHD, AMaZE and RCD in RawTherapee

RawTherapee separates Bayer from X-Trans sensor setups. The Bayer list includes AHD, AMaZE, RCD, and combinations such as AMaZE+VNG4, RCD+VNG4; X-Trans uses another set of methods and does not provide these Bayer options. Similar names do not mean that the algorithms can be compared one by one in different software. 〔G-DEMO-01〕

RawPedia gives limited general advice about its own software: For Bayer images, try AMaZE first for low ISO; try LMMSE or IGV for high ISO; and try 3-pass (Markesteijn) first for X-Trans. This advice is not a guarantee for every photo, and the manual also recommends checking the results with your own camera RAW. 〔G-DEMO-02〕

Use the same RAW for reproducible comparison

Open the same RAW in RawTherapee, keep the exposure, sharpening, noise reduction, scaling and output settings unchanged, and only change the demosaicing method. Zoom in on the preview to at least 1:1 and examine fine fabrics, brick walls, diagonal lines, and high-contrast edges; double-check with both low-ISO and high-ISO samples. Save comparison results by camera model, as different models may have different strengths and weaknesses, and visible differences between algorithms may be subtle. Don’t translate your personal impressions of a single sample into a generic score or fixed ranking for AHD, AMaZE or RCD. 〔G-DEMO-03〕

When to use dual algorithm mode

Dual demosaicing options such as AMaZE+VNG4 use different algorithms for high-contrast detailed areas and low-contrast flat areas. RawPedia points out that the price is that the image has to be processed twice, so it will take more time; whether it is actually worth it, you need to check the details and artifacts on your own images. 〔G-DEMO-04〕

Evaluate false color suppression and demosaicing algorithms separately

RawTherapee's False Color Suppression can perform median filtering suppression of false color artifacts produced in demosaicing, but this process affects color resolution without changing the brightness channel. When encountering colored spots, compare demosaicing methods before evaluating whether suppression is needed; do not describe this as a guarantee that all moiré will be eliminated and all detail will be preserved. 〔G-DEMO-05〕

Lightroom’s Raw Details is another type of processing entry

If you use Lightroom Classic, you can select Raw Details in the Detail panel, and then execute Enhance to generate an enhanced DNG. Adobe describes the effect as sharper detail, more accurate edge rendering, improved color performance, and reduced artifacts; the feature only works with Bayer and X-Trans mosaic RAW, and does not offer AHD, AMaZE, or RCD algorithm choices. JPEG, TIFF, linear DNG, etc. are not supported. When comparing, it should be regarded as an independent processing function of Adobe, rather than equivalent mapping with an algorithm of RawTherapee. 〔G-DEMO-06〕