Auto WB in Color Balance vs. Levels and Color

[tomczak]

I started comparing the two (to understand it better). It looks to me that Auto WB in Color Balance is done on RGB, while Levels and Color uses HSV. Is that true? So far the Color Balance wins, but I don't know enough to make the 'final judgment'.

[jsachs]

It should be the same code -- there may be some differences with the threshold and with the way Dynamic Range is extended. Levels and Color uses the Low threshold setting for Color Balance (see settings menu). Color Balance does not change the black point the way Levels and Color may set the lightest part of the dynamic range slightly differently. I get more or less identical results if I reduce the high end of the dynamic range slightly.

[tomczak]

There are not that much different, but just to show what I'm seeing here is the Compare screenshot of Colour Balance vs. Levels and Colour at default settings. I kind of like what Colour Balance is doing more than the Levels and Colour. The image has plenty of 'white' to anchor on.

[jsachs]

To get auto white balance to brighten the image in Levels and Color you need to auto white balance and auto expand the dynamic range. I don't set this as the default since it would apply every time you started a new image or edited an existing one.

[tomczak]

Yes, I think I did set both in Levels and Colours - it's the tint that auto-corrections get better in Colour Balance, I think. The original image is difficult to auto-correct, to begin with - mixed-light RAW without WB corrections.

[jsachs]

The way I have implemented the items in the Levels and Color settings menu for new images does not work -- will have to find a different method to auto correct, similar to the way Multi Color Balance works now.

[MarkT]

Just a couple of comments/questions about Levels and Color, and DR/WB.

When I launch L&C, the DR is set to full black (the white slider is located to the far left, with the black slider).

The Settings indicate "Don't set Dynamic Range / White Balance on new image".

Clicking either the Full Dynamic Range or Auto White Balance buttons restores the sliders to their "proper" positions, and choosing Reset from the Settings menu places the DR sliders to align with the image ticks on the scale.

If I change the Settings to "Reset Dynamic Range / White Balance on new image" as default, then re-launch the transformation, it loads with the sliders on the tick marks, then if I click the Full Dynamic Range button the sliders go to 0 and 100%, respectively. Then I click the Auto White Balance button, and the sliders return to the tick marks.

Not sure what I'm asking, other than "what am I doing wrong here?"

[jsachs]

Yes, I know it's not working right -- should have a fix later today or tomorrow.

[MarkT]

Ah, I see. Thanks for the update.

[jsachs]

I have reworked Levels and Color yet again for the next release -- sorry for the instability, but there were some structural issues with the previous implementation. It now produces results more or less identical to Color Balance when doing Auto White Balance, and it also works predictably when applied to different images. The single Color Balance color has been replaced with Remove Color and Add Color controls similar to Color Balance. It should still work with old scripts since the old Color Balance color is mapped to the new Add Color and the new Remove Color defaults to white.

If you want Levels and Color to auto white balance, you set Color Balance to Auto White Balance -- this will white balance the current image and all subsequent input images. To white balance only the current image, you then set Color Balance to Custom, at which point subsequent images with color balance consistent with the current image and not be rebalanced.

Similarly with dynamic range which can be Custom, Reset, or Full. Custom means the markers stay in the same place for subsequent images. Reset means the markers are set to align with the tic marks for subsequent input images and Full means the markers are set to pure black and white for subsequent images.