M8 chequered noise pattern - LR3 vs RawTherapee

[fiatlux]

In a few of my 1280 ISO M8 DNG shots, I noticed some kind of chequered pattern in the dark areas (not banding streaking from bright lights in the frame).

Surprisingly, the pattern is much more visible in Lightroom 3 than in RawTherapee, a free converter I don't really use regularly but check once in a while (the latest versions have become extremely good in terms of IQ).

I wondered whether this was a known issue and whether there was any tip to minimise the problem (it is not obvious to post-process out of the image).

 

[jaapv]

The difference is in the noise reduction settings in your raw converter, in theory LR3 can do better than any other converter but you will have to use the sharpening/noise reduction sliders correctly. The pattern itself is caused by massive underexposure.

 

[Gabriel M.A.]

It is also sometimes due to colorspace-related dithering. I always use ProPhotoRGB and 16-bit.

 

[jaapv]

Well-yes that too It is always a good idea to use the largest possible colorspace when postproessing - as soon as one drops down to a smaller space the out-ofgamut colors are lost irretrievably. And using 16 bits will go a long way in preventing posterizing.

 

[MrDan]

are you talking about the "yellowish" tinted noise? ya that bothered the hell out of me with my M8. I guess it's attributed to underexposed shots... it shows up in the M9 as well... i think i have to improve my technique

 

[fiatlux]

Well-yes that too It is always a good idea to use the largest possible colorspace when postproessing - as soon as one drops down to a smaller space the out-ofgamut colors are lost irretrievably. And using 16 bits will go a long way in preventing posterizing.

Sorry I left the thread for so long. I'll try posting samples tonight.

Two clarifications:

1. the pattern I see in the shadows is a regular grid, with lighter noisy pixels than the background noise.
2. I 2x checked and Rawtherapee shows the grid as well as Lr.

 

[Gabriel M.A.]

That's interesting, I'm curious and would like to see it. I wonder if it's something that freaked me out a couple of years ago: one day I saw a couple of shots with strange banding on a bottom corner (I forgot if it was left or right), noticeable only when it was underexposed. Then nothing. Then a week later it happened again, although this time I noticed it while I was double-checking on the image to see that it had been properly focused. I moved to a different place away from the sunlight. Tested again. Gone. Went back. There it was again.

I soon realized that it was a friend's BlackBerry. All the shots I took right next to him exhibited this. I think that the M8's "abundance" of metal makes it prone to this curious little phenomena. I've tried replicating this with my 5D and kind of saw something different, but negligible.

That said, it only happened that one month a few years ago. And I'm sure somebody on the Intertoobes is going to run with this and cry fire.

But anyway, something to consider. I arrive at "whys" due to my troubleshooting nature (both at work and outside).

 

[Mudman]

Can you post samples?

 

[fiatlux]

Here's a 100% crop of a shadow area out of a 1250 ISO image in Lightroom 3 (default import settings). You can see the faint blue grid. Difficult to process out.

 

[jaapv]

Yes- that is normal for deeply underexposed areas, can easily be removed by correct raw conversion in ACR 6.0