The X20's Green Problem

Started May 3, 2013 | Discussions thread
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Nukunukoo Regular Member • Posts: 358
The X20's Green Problem

After reading DPR’s excellent review of the X20 some of the problems they pointed out grabbed my attention. Specifically, the way the X20 (or probably the X-Trans in general) captures green subjects. While most small sensor compacts smudge images at low ISOs, the X20 smudges green details more than expected.

This brings me to the suspicion that the X-Trans sensor could be the main cause of this.

If you look at the X-Trans color array, it covers a 6x6 pattern as opposed to the Bayer’s 2x2. Furthermore, smack right in the middle of the X-Trans matrix is a solid block of 2x2 green. This relatively huge area does pose a demosaicing challenge.

The X-Trans 6x6 pattern with a 2x2 green block in the middle.

I wanted to do a quick test to see if the X20 does treat anything green differently from the rest of the colors, namely, red and blue. Still on a holiday, all I have at my disposal (besides my X20) are my Mac Air and Samsung 7.7 tablet. I created three single colored spiral images for each of the RGB colors, where each individual RGB color is given its max value (255/FF) and assigning a zero to the other two colors for each image.

Since my Mac was a non-retina version, I opted to capture the images on my Tab 7.7, which has a respectable DPI of 196 and is currently the biggest SAMOLED display in production so I have no doubt with regards to its contrast and saturation. I seated the X20 on top of a book (my Gorillapod is with a friend at the moment). All things considered, this is as scientific as I can get!

The Samsung Tab 7.7 testbed.

I also included a black spiral for reference (now that I think about it, a 50% gray would have been better!). Below are the four color swatches cropped and increased by 400 using the Nearest Neighbor method to eliminate any gradient interpolation. The images were taken from RAW to remove any JPEG-engine related color bias and opened in LR5. LR5 is only used to open the captured images and no post-processing was used including NR and sharpening.

Green (400%)

Blue (400%)

Black (400%)

Below are the images side-by-side in both color and grayscale.

The images next to each other

In grayscale

Notice the pronounced vertical artefact on the green spiral. This artefact is also visible to a lesser degree on the blue image, which is not surprising since blue is a component of green. It’s hard to conclude that the X-Trans is to blame: conducting a similar test with all of the X-Trans Fuji is needed. What this experiment do show is that the X20 images exhibit some green and blue artefacting.

In all fairness, with my real world tests (showing my works, both printed and onscreen) to fellow colleagues, they did not notice anything off with my JPEG images until I asked them to pixel-peep on specific areas that was most affected by the artefacting. Even then, they needed to be told that something was off.

Still, this does not mean all is forgiven. Whether a firmware upgrade is a solution or that the X-Trans sensor’s big green “hole” has an inherent flaw, Fuji needs to address this issue to clear the air for current and future X20 users.


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