A script to calculate blur length on a shadow.

Rod · **Joined:** May 16, 2010 **Posts:** 16070

For shadows with perspective is it possible to use a path line with three points to calculate the blur length at the end of a shadow to make it look blurry further back and gradually get solid and more realistic looking? This would allow you to have a custom blur for any shadow. The current Perspective shadow blurs the entire outside or radius of the shadow and doesn't look very real. Or am i missing a setting within the filter to fix that?

paynekj · **Posted:** Tue Nov 12, 2013 12:17 pm **(#2)**

I don't know of a way to do it as you describe, but what you seem to be requiring appears to be what the focus blur plug-in does.

You would have to create the Depth-Map manually, but then I suspect that the amount of blur is subjective anyway.

And apparently you don't need to be told where to find a copy of the plug-in

Kevin

ofnuts · **Joined:** Oct 25, 2010 **Posts:** 4812

Still looking for a technique for realistic shadows... Plain blur doesn't work because is expands the shadow, while the shadow get gradually thinner than the object that casts it.

Graechan · **Posted:** Tue Nov 12, 2013 11:18 pm **(#4)**

Rod is this close to what you mean

lylejk · **Joined:** Sep 24, 2010 **Posts:** 12781

Now that's cool Graechan. Link to Script-fu?

Graechan · **Posted:** Wed Nov 13, 2013 1:35 am **(#6)**

Lyle I'll post tomorrow but it's simple: 'perspective shadow' then add a white-mask on the shadow layer and blend with gradient FG/BG (black and white) from top to bottom on the mask.
Not sure if it's what Rod wanted though

molly · **Joined:** Apr 07, 2010 **Posts:** 14182

Now that is some shadow Graechan, I don't know how you did it but I would sure like to have it.

paynekj · **Posted:** Wed Nov 13, 2013 7:11 am **(#8)**

This is what I would do:

Attachment:

blur_perspec_shadow.png [ 20.87 KiB | Viewed 3928 times ]

Which is a perspective shadow, with a focus blur using a black to white gradient as a depth map to get the "deeper" areas increasingly blurred, then a layer mask using the same gradient to fade the shadow.

.xcf attached

Kevin

(actually what I would really do is use POV-Ray to render it properly

)

fluffybunny · **Posted:** Wed Nov 13, 2013 7:22 am **(#9)**

Is it just me, or in Graechan's result does it not make the letter 'P' seem closer to the viewer than the other letters?

Rod · **Joined:** May 16, 2010 **Posts:** 16070

Fluffybunny you are correct.
Thank you Kevin and Graechan that is almost perfect. Just needs more sharpness at the front of the shadow i think.

I was checking out the follow path plugin that was recently added to the registry.
http://registry.gimp.org/node/28647
I wonder if a blur option could be added to this filter as a option to gradually blur a perspective shadow? I asked the author to look into it.

molly · **Joined:** Apr 07, 2010 **Posts:** 14182

guess I just got n'jd. lol. I was looking for my post and wasn't there, Yes Fluffy I also agree that it looks closer but maybe it is because the tail on the p goes below the bottom of the other letters. Tjhe script is really looking good though.

paynekj · **Posted:** Wed Nov 13, 2013 3:49 pm **(#12)**

Here's what I get using POV-Ray

With a single point light source:

Attachment:

shadow_point.png [ 116.42 KiB | Viewed 2867 times ]

With an area light (14x14 point lights over a 2x2 area):

Attachment:

shadow_area.png [ 121.78 KiB | Viewed 2867 times ]

Some odd artefacts, but you get the idea.

Kevin

Rod · **Joined:** May 16, 2010 **Posts:** 16070

paynekj wrote:

Here's what I get using POV-Ray

With a single point light source:

Attachment:

shadow_point.png

With an area light (14x14 point lights over a 2x2 area):

Attachment:

shadow_area.png

Some odd artefacts, but you get the idea.

Kevin

Yep. The closer the shadow is to the object casting it the sharper it should be.

abraess · **Joined:** Oct 02, 2010 **Posts:** 106

I think that you can only fake because you need hight object distant for Light and angular of light for make real. The best would take render Model scene and work with photo as base.

molly · **Joined:** Apr 07, 2010 **Posts:** 14182

Yes, the second one looks much more realistic. good job Kevin and Graechan for working out the kinks.

Graechan · **Posted:** Thu Nov 14, 2013 7:42 pm **(#16)**

I think we all agree that the perspective shadow in Gimp falls slightly short of what we would like
below is simple solution for 2.6 and 2.8

Rel2 script below↓

Attachment:

Perspective Advanced.scm [5.53 KiB]
Downloaded 152 times

K1TesseraEna · **Joined:** Sep 22, 2012 **Posts:** 2089 **Location:** US

Haven't checked your script yet Graechan but this is a good gimp tutorial on creating realistic shadows
http://gimp.pixtuts.com/gimp-tutorials/ ... tic-shadow
Is it possible for you to make a script out of this?

Graechan · **Posted:** Thu Nov 14, 2013 8:15 pm **(#18)**

K1TesseraEna if you read the script then it's what I have done but thanks for sharing the tute

Rod · **Joined:** May 16, 2010 **Posts:** 16070

Graechan it seems to be in the menus as "<Image>/Filters/Light and Shadow/Perspective Advanced"

My settings

My results

Now i just need the lighting within the shadow.

I will play around with it some more.

Rod · **Joined:** May 16, 2010 **Posts:** 16070

Here is the results after using your Perspective-Advanced script (same values).
Then i selected the bottle layer and ran Shadows&Highlights script on the bottle then using transform to correct the angle over the Perspective-Advanced shadow layer and voila. Oh i did have to create a new layer with a white shadow under all the other shadows.