[Darktable] Quick White Balance in Darktable

[Andrea B.]

I wrote this down so I would have a reference. And if I write something down, it sticks in memory better.

 

NOTE: This is for my older version of Darktable. I will write one for the latest version soon.

 

Darktable for Quick White Balance.

 

Send the file to Darktable.

Right-click & Edit Photo with Darktable, or

Drag-n-drop onto Darktable icon.

File comes up as a thumbnail in Lighttable.

Double click thumbnail to bring file up in Darkroom.

 

Darkroom

Click Active Modules icon.

(Leftmost in icon row on right panel below the histogram.)

 

Click Output Color Profile arrow.

output profile = Adobe RGB.

Click Output Color Profile arrow.

 

Click Input Color Profile arrow.

input profile = standard color matrix. (Just a working space.)

gamut clipping = Adobe RGB.

Click Input Color Profile arrow.

 

Click White Balance arrow.

Click camera arrow.

Select Spot from drop-down menu.

Draw white balance marquee over desired area of photo.

Click White Balance arrow.

 

While you are here in the Darkroom, you might want to use the Histogram

to adjust the white/black points. It's very easy.

Go to the histogram icon and click up linear view. (1 of 3 histo views.)

(Leftmost icon, on top right in histo box.)

With cursor over right 3/4 of histogram,

drag the lit up area to the right to increase brightness.

With the cursor over the left 1/4 of histogram,

drag the lit up area to the left to improve dark areas.

Double-click any part of the histogram box to reset.

 

Click Lighttable at top right to begin export of white-balanced file.

 

 

Lighttable

Select the thumbnail for exporting.

Click Export Selected arrow.

The following settings will remain until you change them.

So the only change needed for later exports is usually just the storage folder.

 

Storage Options

target storage = file on disk.

Click file icon to select storage folder.

on conflict = create unique filename.

 

Format Options

file format TIFF (8/16/32-bit).

bit depth = 16 bit.

compression = uncompressed.

 

Global Options

max size = (ignore).

allow upscaling = no.

profile = Adobe RGB.

intent = perceptual.

style = none.

 

Click export.

 

 

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Shorthand

Darktable > Thumbnail > Active Modules > White Balance > Spot > Marquee.

Histogram > Linear > Drag > Drag.

Lighttable > Export Selected > Storage Folder > Export.

 

 

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[Doug A]

I wrote this down so I would have a reference. And if I write something down, it sticks in memory better.

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Looks good. Appreciate all the work you put into this site.

Thanks for the tutorial,

Doug A

[Guest]

When do you convert the final image to 8bit sRGB for web viewing and how do you manage the color shift from the reduced gamut?

[Andy Perrin]

That should always be the very last thing you do in order to maintain the quality up until it's absolutely necessary to reduce it. I don't think you can do anything about the color shift. For one thing, as we were discussing on the board here not long ago, we are all using different display devices, so it's not like we are all seeing the same thing anyhow.

[Guest]

I see. WB probably isn't impacted by downsampling the bit depth and color space. Just curious if it was part of the DT workflow.

[Andy Perrin]

I see. WB probably isn't impacted by downsampling the bit depth and color space. Just curious if it was part of the DT workflow.

That depends on what you mean by that comment. It definitely matters what order you do things in. If you downsample the bit depth before you WB, you will get horrible results. This is why trying to WB a JPEG is usually hopeless. It must be done at 16 bits.

[Guest]

I was considering it as last step.

 

Interesting, I never considered performing WB in Jpeg as problematic. I should pay closer attention or at least compare.

 

I do WB in 12/14bit RAW when I can. Though, sometimes I tweak the WB after I have exported to Jpeg.

 

However, I shoot in sRGB.

[Andy Perrin]

The data in the RAW is digitized at 12 or 14 bits. But usually we store it in 16 bit numbers (2 bytes). That also gives some headroom to avoid roundoff error. I think WB on a JPEG would be less problematic in visible light (and perhaps IR). The extreme white balances that we use for UV do not play well with JPEG. Take any poorly white balanced UV image on this board and try to "repair it" and you will find you can't always do a good job.

[Guest]

Ok, I get that.

 

As a matter of practice what would I look for in a UV image to determine the WB is not properly repaired. For example, will there be stray colors and what would they be? Maybe, I need a visual aid.

[Andy Perrin]

You should not see any trace of red or magenta in the image if it's in our standardized white balance (in other words if PTFE is white in the image).

 

For example this image is not quite right because of the warm tones:

https://www.ultravio...ected-uv-photo/

 

For some correct examples, look at any of these:

https://www.ultravio...6-brassicaceae/

 

The usual tones are blue, gray, black, yellow, rarely some green. This is because two of the color channels are almost perfectly correlated, so in reality we don't have three independent colors, we have two independent values and the third can be computed. Just for fun, I wrote a program to convert an visible light photo into the UV color palette:

https://www.ultravioletphotography.com/content/index.php/topic/3479-heres-something-to-discuss/page__view__findpost__p__30024