My Lumix lz4

[Sandrine Bascouert]

I've a small point and shoot lumix TZ4

http://www.letsgodigital.org/en/18178/panasonic-lumix-tz4/

And I've noticed that all my images and especially in low light have some kind of blotchiness in the blue channel

Blue channel

All channels
​

It doesn't look like noise. Is anybody know where it comes from (apart from replying it's coming from the sensor of course ?
If I understand what it is, I'll be able to correct it and "actionize" it in Photoshop....(or in Camera Raw)

 

[Bart_van_der_Wolf]

I've a small point and shoot lumix TZ4

http://www.letsgodigital.org/en/18178/panasonic-lumix-tz4/

And I've noticed that all my images and especially in low light have some kind of blotchiness in the blue channel
[...]
It doesn't look like noise. Is anybody know where it comes from (apart from replying it's coming from the sensor of course ?
If I understand what it is, I'll be able to correct it and "actionize" it in Photoshop....(or in Camera Raw)

Hi Sandrine,

It's caused by:
1. Few photons being registered by the Blue filtered sensels of your camera's sensor array.
2. The subsequent demosaicing based on that low signal-to-noise data in the Blue channel.

There are only 2 cures.

First is, if anyway possible, to improve the exposure in the Blue channel. Either by using a longer exposure time (without overexposing the Red and Green channels), or when you cannot avoid clipping Red and Green, using a lens filter that is somewhat bluish (thus modifying the exposure balance to something closer to your sensor array's optimum). I am assuming that using artificial lightsources is not possible, otherwise one can add one's own light to the scene.

Second is in post processing, by using noise reduction, in particular in the Blue channel.

Cheers,
Bart

 

[Sandrine Bascouert]

Second is in post processing, by using noise reduction, in particular in the Blue channel.

That's what I usually do, At first I thought it was ONLY on low light photos but just discovered that it was present in all of them, at various degrees...
Thanks!

 

[Bart_van_der_Wolf]

That's what I usually do, At first I thought it was ONLY on low light photos but just discovered that it was present in all of them, at various degrees...
Thanks!

Hi Sandrine,

Yes, the blue channel sensitivity differs between cameras. For the best image quality one would need to find out how the Raw data is distributed for a capture of a neutral surface. If one shoots an image of a neutrally reflecting wall (assuming no optical brightners) the Raw data should show a histogram with 3 humps in roughly the same spot, but after White Balancing and Raw conversion they will always be in the same place. So one needs the possibility to study the Raw data before any processing to see if lens filters would improve things.

Cheers,
Bart

 

[Sandrine Bascouert]

I don't know how to do that when my camera only output Jpeg image

 

[Bart_van_der_Wolf]

I don't know how to do that when my camera only output Jpeg image

Hi Sandrine,

One can only experiment with Blue-ish colored filters then, and see if the blue channel quality improves compared to Green and Red. There must then also be a possibility to use a custom white balance to prevent the JPEGs from becoming too Blue.

Maybe it's unfortunately the way that camera is, and little can be done to improve up front.

All that rests then is postprocessing. Noise reduction in ACR6.2 has become quite good, and you can import a JPEG as an ACR-Raw in Photoshop CS5. That would allow to tackle some of the noise, but re-saving JPEGs is also not without losses. When you start with Highest Quality JPEGs, you may have a reasonable stating point.

Cheers,
Bart

 

[Sandrine Bascouert]

One can only experiment with Blue-ish colored filters then, and see if the blue channel quality improves compared to Green and Red. There must then also be a possibility to use a custom white balance to prevent the JPEGs from becoming too Blue.

I think I can do that...

I'll probably have to experiments with the same subject at different settings (Iso etc...) to determine if I need one action per setting or if I can script it for all the types of files...

Thanks a lot for the explanations!

 

[Cody White]

Sandrine,

I hope this is for your camera:
http://service.us.panasonic.com/OPERMANPDF/DMCTZ4.PDF

It looks like you can set your color mode.

 

[Sandrine Bascouert]

Yes I know' but it's just a saturation/ hue changing mode i don't think it affect the sensor rendering but just the post treatment of the image by the camera chip.
You can set it up by using natural/vivid/black and white/sepia etc...

Thanks anyway...