Tuesday, July 24, 2012

[PureView Test] Red tint issue with photos !

Posted on 11:29 by SlipKoRnSaad

Hi there,

Today i wanted to share with you my impression about an important point that nobody seemed to care about, and i have been complaining about it several times on twitter and even Damian couldn't give me a feedback about it till know.

This issue really is bothering me a lot, because, my N8 for example don't have that, nor the much controverted iPhone 4s (sorry to say it, but it's one of the best camera device out there for many reasons that i can discuss in another post).

So what is all about? Simply a disturbing red/pink tint in some situations that gives the impression of an early 2005 camera issue seen on the N95 and N82 at some extents...

Let me clarify with an example :

Do you see the color rendering in the background (the wall)? Ok, do you see some pink hue as i do? Ok. Well, actually, the wall isn't "pink" but "white" !

For example, the N82 of 2005 has done this :

What do you see? Right !

Well, while it's true that the 808 is warmer, it doesn't mean that the color rendering is close to reality in this situation...

In my mind, the first thing i though, is that the 808 was fooled by the surrounding pink colors tones (the duck, drape etc)

But let's take another example :

Hum what's we've got here? The same pink hue, there's almost nothing pink (excluding the little knife on the top right) !

I did pratically the same shot with the iPhone 4s and i get this :

Exact, no pink hue and it's partially due to the under-exposition, but the result is fine with that...

I did some tweaking with RGB setting with the help of the default editor on the 808 and i've got this :

If i reduce "red" tone to -5% it'll look like this :

If i make it down to -10% it looks like this :

Almost perfect (but it tends to be blueish a little bit) the white looks "white" and not pink :) (even if another issue appears : overexposing)

So yeah, the solution is here, is to fix RGB management when flash is "on", if the iPhone can do it, you can do it, even better ! If the 2005 N82 can do it, the revolutionary 808 can do it ;)

I really hope to see this fixed as the issue doesn't appear on "normal" (daylight or when the flash is off) situation but mostly when the flash is fired on and on a "white" background...

EDIT : while i was reading the technical PR from Nokia i did find probably the answer of this issue :

...oversampling eliminates Bayer pattern problems. For example, conventional 8MPix sensors include only 4Mpix green, 2Mpix red and 2Mpix blue pixels, which are interpolated to 8Mpix R, G, B image. With pixel oversampling, all pixels become true R, G, and B pixels. What’s more, based on Nyqvist theorem, you actually need oversampling for good performance...

In other terms and if i understand tat corretly it's what's causing "more red" (and blue) which causes purple/red tint issue :)

Ps : the color and saturation setting on creative mode didn't do the magic as the inbuilt image editor and frankly i don't want to "play" with setting to get a "normal" rendering ! I want it to be ALL DONE OUT OF THE BOX :)

For the fun look at the top (by right) of the picture (well i cropped it for you), the xenon flash and speed are doing their magic !

Yep, a little fly ;)

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