Difficulty with Blurs and Masks

Processing
1

Hi,

I’m having some issues applying a small “natural” looking blur to the background of this image, using the Blurs module.

I’ve used a drawn mask. Other people in the picture (not shown in attached example) have colours that are similar to the background, which has ruled me out from using a parametric mask. It might be possible, but not yet for me.

I’ve read in other posts different limitations with the Blurs module, so if there’s a better module for me to be using, please let me know. For me, it is giving the nicest blur effect. Remember, I want to keep it natural, so I’m only looking for a slight blur to add some separation between the subjects and the background.

Easter Blur
Easter Blur1708×896 526 KB

Sorry, I’m not able to attach the RAW image to the post, because I would like to keep my family and friends off the internet, at least in family shots anyway. (We’re all out there somewhere!)
I have looked through the PlayRAW section in an attempt to find a similar situation and there’s not too many images that I could find with people or subjects in front of busy backgrounds. The best I could find was: Two Taiwanese uncles playing chess

In the attached jpg, I’ve pointed to 2 areas where I am having the opposite problem.

On the ears, I have pulled the mask back away from the edge and have let the feathering go up to the edge. This blurs the edge of the ears, along with the background, which isn’t what I want.
(There is also a small gap I missed at the base of the left ear, where the background isn’t blurred. See my next try for more on that.)

On the arm and shoulder, the edge of the mask is almost to the edge of the subject. This shows a noticeable halo to me, which again, isn’t what I want.

I have been able to succeed using drawn masks with colour and exposure adjustments to nicely separate the subject and background, but using a mask and a blur seems to leave obvious artefacts, to me at least.

Feel free to point me to any tutorials or previous posts that would help me out.

Thank you in advance for your help,
GJ

2

try using the Feathering radius on your mask.

3

Try tweaking these

image
image493×223 5.95 KB

rather than trying to use the drawn mask object “feather” ie the dotted graduated boundry.

Contrast and feather can often really clean up the mask

4

You could refine the mask based on detail levels. The subject is generally sharp, the background blurred. See details threshold: darktable user manual - mask refinement & additional controls

5

I’ve had good luck using the bloom preset of diffuse or sharpen, for example see here:

6

In my view and experience what you are wanting to do is incredibly difficult because it is nearly impossible to avoid halos. However, the bloom option preset of diffuse or sharpen module would be my go to in Darktable. However, this sort of work I am more likely to use a layers and masking techniques in GIMP

  1. Open up the image of the people in GIMP and create a duplicate layer

    1. Go to Filters > Blur > Lens Blur and adjust the radius to get the desired amount of blur for the background. I often use Gaussian Blur but some pictures may benefit using motion blur to imply motion instead of Gaussian blur. Others may benefit from Circular, Linear or Zoom motion blur instead of the lens blur filter.
    2. Activate the second layer, move it to the top of the stack and add a white layer mask and ensure the invert mask box is not selected.
    3. You then need to use a paint brush with a 50% hardness and black paint to paint in the areas you want blurred. If you make a mistake then switch the paint to white and erase that area of the mask.

With lots of patience this can be achieved in GIMP and would suspect a lot easier than in DT. This would also be one of those cases that AI might have the edge, but that option is not available in DT or GIMP.