Bug? Levels: Black Level and Output Black Level together

[dmstraker]

When using the new Levels, it seems to map to Curves with the old Black Level and White Level moving the left and right nodes horizontally, and the new Output Black Level and Output White Level moving the Curves nodes vertically.

All well and good. But it gets a bit odd when using them together. Move Black Level and Output Black Level up the same amount and you seem to return to the original image, rather than having the black point shifted and it being a big whiter overall. I've tested this on PS (CS6) and it seems to work 'correctly' there.

Here's a video showing what I mean.

 

 

[lepr]

.

[dmstraker]

Aha! Thank you. This explains the cancellation effect when using both sliders.

It's confusing as the Curves vertical axis is Output, making Output Black Level seem to correlate with this.

Still puzzled about PS being different. 

[dmstraker]

Don't know where you are with this folks, but I'm pretty convinced the current implementation is incorrect.

The 'Output' slider should work on the vertical axis. It kind of does as in >I< example above, but fails when combined with original Black/White level adjustments.

Look at the way Photoshop does it. This is how it should be.

Thanks!

[Chris B]

Hi Dave,

We haven't forgotten about you.

I had written a big reply but before I unhide it, can you attach a real-case file where the different behaviour in Affinity is causing a problem. The reason I'm asking for this is because I've done my own comparisons in Photoshop and Affinity and it seems to be working similarly. The values are different as we use percentage so I've been doing 25% and 75% whereas in Photoshop I've been using 64 and 192 in the Levels sliders.

Also, make sure that Affinity isn't using the Printer Profile which was discussed in this thread:
https://forum.affinity.serif.com/index.php?/topic/77085-gradient-map-add-point-by-click-not-picking-up-underlying-colour/&amp;tab=comments#comment-402888

 

It could potentially be causing you to see wildly different results if Photoshop isn't doing the same...

[dmstraker]

Hi Chris.

Here's another video demonstrating the effect on a real photo, showing it in AP and PS, Curves and Levels. I think it's pretty clear that the 'Output' sliders should work as the Curves vertical axis, not the horizontal one. Yes, if you use the Output alone, it will look like you're using the vertical axis, as illustrated in the image by >!< above. The problem happens when you try to use both of them together. As implemented, you might as well have it on a single axis, starting in the middle of the scale.

I also show in the video that the profile is sRGB. In any case, when the same image is used in AP and PS, similar results should, in this case, I presume should be achieved.

Cheers!