New camera, first tests and a long story to tell

[Stefano]

So to white balance off-camera my images I can just set a neutral white balance (like setting it in deep IR, as Andy once suggested) and then "white click" in RawTherapee, provided it has this feature?

[dabateman]

Just click around the image with the dropper tool like Andrea does until you find something you like. She goes after a magenta looking thing. But that will depend on your sensor, lens, filter and light.

[Andy Perrin]

You can definitely get unwhitebalanced colors in PhotoNinja simply by unchecking all the boxes except deMozaic. I don’t know how to do it otherwise except by tricks like white balancing in camera in 850nm+ IR. I suspect that exiftool can do it also, and that is free.

 

If you want to white balance UV then you don’t need unwhitebalanced colors, you just need to click something magenta in a program capable of setting UV white balance.

[Stefano]

...I tried it, and it didn't work. I put a "Sunny" white balance and took a test image with a UV-purple lens (the same lens Bernard asked if it was plastic), 2 mm thick ZWB2 glass (I have two pieces, I use one on the camera and the other one is just "free"), the Rubik's cube (I am curious to see how it comes out), and a paper tissue as a white reference. I have both the .CR2 and .JPG versions, I will post here the resized .JPG. By "white clicking" I was not able to get a proper white balance. Clicking in darker areas improved it, but it wasn't satisfactory. Am I doing something wrong?

 

[bvf]

Thanks. I installed RawTherapee and opened the image, but I still see the white balanced colors. How can I see the "true" colors? I did a quick search online and didn't find how to do it.

 

Stefano - by default, RawTherapee uses the WB provided by the camera. Here is what I do ...

 

Photograph a suitable neutral white or grey target using the same lens/filter/lighting combination - PTFE/Teflon is a suitable target. Make sure you don't over-expose so that the image is burnt out. If you haven't got PTFE, use white paper for now just to get going - you can get sheets or tiles of PTFE on ebay.

 

Open the RAW of your target photo in RawTherapee.

 

In RawTherapee open the Colour menu (3rd symbol from left near top-right of the screen).

 

Under White Balance, click on "Pick".

 

Then click on the image of tyour target - this should now turn white or grey,

 

Save the WB profile by selecting the floppy-disk-with-down-arrow at top right of your screen, and give the profile a suitable name.

 

Now load the photo you want to WB.

 

From the open-folder icon at top-right, select your WB profile. Your image should now be WBed.

 

Let me know how you get on.

[nfoto]

Paper tissue is not a good choice for setting "UV white" balance. Optical brighteners might be added to it and that would throw off any attempt of w/b.

 

RawTherapee is not as good as for example Photo Ninja for making a decent "UV white" balance. Sometimes one has to introduce extra steps in order to get a passable outcome.

[Stefano]

I will try as Bernard described.

 

I know that a paper tissue is not an optimal standard, but works well enough for me. The one I have fluoresces very little under UV, and it isn't like copy paper that has a bright blue fluorescence.

[Cadmium]

I have seen people use Styrofoam, seems to work pretty good.

[Stefano]

I tried. No matter where I click, the image stays pink. It seems it doesn't change. I saved the profile and used it with an image, but it just made it brighter, the pink cast remained.

[bvf]

Stefano - do you have a Dropbox account? Perhaps you could let me have your RAW image to play with?

[Stefano]

Here's my test. Since the Sun is gone now where I live, I had to make my artificial Sun by running a 50 W 12 V tungsten lamp (the type with a reflector) at 5 A, 17.5 V (almost 90 W). They won't last long used this way, but it didn't fail yet. Here I am posting .JPGs, but I have the .CR2s of all images, since I am now shooting in RAW + JPG.

 

Sunny white balance, paper tissue:

 

Sunny white balance, test scene:

 

Test scene white-clicked in IrfanView:

 

Test scene (a different photo, but taken without moving the camera) using the first image in this post as the in-camera white balance target:

 

(also, the last image required almost three stops more exposure than the second one (4 seconds vs. 30 seconds)).

 

The images are not in perfect focus, but here it isn't important. I tried to focus the best I could, but the live view was too dark.

[Stefano]

Stefano - do you have a Dropbox account? Perhaps you could let me have your RAW image to play with?

I don't think I have Dropbox, but I should check.

 

Yes, I have it, but I never use it and I don’t know how it works. Can you please explain me what I have to do?

[bvf]

Can you please explain me what I have to do?

 

I'll try to remember how to get started!

 

Do you have the Dropbox app on your PC, and do you have a Dropbox folder when you go into Windows Explorer that looks like this?

 

 

If you do not have these, you need to download the app from https://www.dropbox.com/install

 

When you have these you need to create an logon, if you have not already done so - at dropbox.com. You can get a 1GB account for free, although they will encourage you to get a paid upgrade.

 

Then you should just be able to drop a file into the Dropbox folder in Windows Expolorer. Then go to your Dropbox.com account, click on the file, and click on Share. Then use Share Link: this will put a link into your clipboard. Then send me the link using UVP Messenger.

 

It's not as hard as it sounds!

 

BUT before you do that, try emailing me the RAW file. It may be too big, but it may work. I will send you my email address via UVP Messenger.

[ulf]

Here is more detailed information about ETTR that i dug out from the RawDigger website.

https://www.rawdigger.com/howtouse/beware-histogram

Even if you are not using the RawDigger it is useful for understanding how miss-leading the camera's exposure information might be.

[Andy Perrin]

Yeah. I have found you can mentally adjust for the inaccurate readings to a large degree. I never use the cameras auto features for determining exposure with UV photography. I do everything manually.

[Stefano]

Bernard tried to white balance my RAW files and he too wasn't able to do it in RawTherapee. He then discovered the green channel is completely missing, and this may be the reason (or part of it) behind this problem.

 

Does anyone have experience with this issue?

[Andy Perrin]

Stefano, do you want me to try in PHotoNinja also?

[Stefano]

Why not. I think I already have your e-mail address, I will send it to you.

[Stefano]

No, you have mine, is the other way around.

 

Just noticed I can still find your e-mail address since you sent me an e-mail.

[Andy Perrin]

Yup, okay, this is what I got (operations were: white balance off tissue, denoise with Neat Image, exposure adjust, and shrink and save as JPEG).

[Stefano]

Well, it worked!

[Andy Perrin]

I would conclude that you are not missing any channels, but I don’t know what to recommend for a RAW converter if PhotoNjnja is unavailable.

[bvf]

As Stefano said, the RawTherapee auto-WB would not work, and the green channel was absent according to the Navigator tool. But if you played around with the channel mixer (inc. winding the green channel up to 500%) you could actually get a result, but it took a lot of effort and still wasn't as good as the in-camera custom WB which produced a good WBed JPEG.

 

After giving up with RawTherapee, I tried again with Dark Table. This is another free RAW processor, but I haven't yet got the hang of the interface. Anyway, the auto-WB did work there, but the image needed quite a bit of processing (brightness, contrast) to get a reasonable image - as Andy needed to do with PhotoNinja. The image was still noisy compared with the in-camera JPEG - so something else was needed.

 

But if the auto-WB is working properly in the software you shouldn't need to do all that other post-processing. So I think there is still a problem with Stefano's RAW images, with a very low green channel. In our discussion we thought the root cause might be the combination filter (ZWB2 + BG39), because other filters like Baader and ZWB1 + S8612work fine.

[Andy Perrin]

But if the auto-WB is working properly in the software you shouldn't need to do all that other post-processing. So I think there is still a problem with Stefano's RAW images, with a very low green channel. In our discussion we thought the root cause might be the combination filter (ZWB2 + BG39), because other filters like Baader and ZWB1 + S8612work fine.

I don't think it's a problem with the filters so much as just an underexposed image. This is what I see for the pre-WB histogram. Plenty of green in the relative sense, but waaay underexposed overall.