Originally posted by biz-engineer How can uniWB work on a Pentax camera.
There is no problem using uniWB with pentax cameras, the challenge is finding the WB setting that give you uniWB.
Originally posted by biz-engineer I have an issue because the Pentax light meter looks at R, G and B channels to optimize exposure, so, depending on the actual incoming color mix, the exposure amount changes.
uniWB is not for calibrating your camera metering system, where it is useful is setting up your cameras play back feedback as to how the image is being stored within the raw file
Originally posted by biz-engineer How can I use UniWB on a Pentax camera? Does this mean I can look on the camera at G channel histogram and ignore R and B channel?
It depends on the luminate that is your light source, for the sun the red channel falls well below the other 2 channels
Here I have exposed very far to the right and as you can see the red channel is not even clipping
Here I am using an exposure that again is further to the right and in the reds of the car are not close to clipping but the tent in the back ground is clipped, this brings me to a point that I have said regularly, if you are shooting with the sun as your illuminate and you are setting your exposure base on a white card or you have a white object that is found in the frame and that white target is not showing any clipping in the greens and blues your reds are pretty safe . So for sunlight you can ignore the red channel unless you are photographing a sunset then you will want to keep track of your red channel.
Not having a RGB histogram in LV is not only a problem with pentax cameras.
Using the spot meter is one of the techniques that I use for anytime chimping is not workable. What I do is set the camera ( for Nikon +1 13) pentax +0.7 to + 1, this is not so that the camera adds that + to the image, but rather allow me to see beyond what my meter can display when I place my spot meter on where I want the white point to be. For Nikon I would need the metering display to show all the way up to +4 1/3 in the display. Basically I am applying an offset to the metering system so that any white target that falls at 2 2/3 scale closely resembles where that white falls within the raw file
Here I metered in red and with the correct offset I know how that white target falls within the raw file, without the offset and I place the spot meter over that target it would only show +3 without knowing how far beyond that 3 I am going. With the offset I have decided and metering on that target falls bellow +3 I know its not going to clip and click easy ETTR.(also take notice as to how the red channels was captured) Check the playback image with uniwb setting and the profile and see if you have any hotspots and your done.
---------- Post added 10-06-2021 at 08:10 PM ----------
Originally posted by biz-engineer When using various WB are applied to the same Raw file, it looks like the green channel histogram is fixed with the red and blue histograms move around.
If you really want to see how the channels relate to how they are captured
go into the exif and change line C628 to 1,1,1 and in your raw converter select as shot for your white balance and now you are viewing it in uniWB
---------- Post added 10-06-2021 at 08:32 PM ----------
Also if you look at the Baseline Exposure that is what is telling your raw how to handle the raw file
If your are using most raw converters and you what to see a more accurate raw file for processing take your BLE adjust your exposure value slider by -1 and then - the BLE = how far you move the slider
For the k5 as shown above -1 +0.5 = 0.5 is how far you move the slider ( the K5 showed -0.5 so that becomes +0.5 two negative make a right
)
Depending on the converter the brightness, contrast and black will very
Some good reading if you have sometime
https://www.rawdigger.com/howtouse/deriving-hidden-ble-compensation https://photographylife.com/where-are-my-mid-tones-baseline-exposure-compensation The Optimum Digital Exposure - Luminous Landscape
If you are shooting red objects and you want the best out of them here is a good read
https://www.libraw.org/articles/magenta-filters-on-digicam.html
For the last couple of years I have been using Magenta filters for photographing red flowers and it really brings out the fine details that can be lost to noise in the reds
Here is what the raw file looks like in sunlight as you can see the red is now shifter to the right and more equal to the other 2