~ • GIMP Chat

GnuTux · **Posted:** Sun Aug 31, 2014 9:43 pm **(#2)**

That's a pretty bad case but there are several smoothing algorithms under the "Repair" menu in G'MIC, which do a pretty good job of gradient smoothing. Anisotropic and its variations, likeThin Brush, have gradient smoothing parameters.

saulgoode · **Posted:** Sun Aug 31, 2014 10:53 pm **(#3)**

Try using Adaptive Supersampling and, if needed, increase the Max Depth and decrease the Threshold.

Preset file for above Tool Preset can be downloaded from http://barn.kerosenecow.net/u/saul/m/su ... eset-af9a/

GnuTux · **Posted:** Mon Sep 01, 2014 1:20 am **(#4)**

Oops... sorry, Zeo. I thought you were attempting to repair an existing image gradient. I see now that is not the case. Guess that's what I get for skimming your post, rather than reading it. :oops:

Zeo · **Joined:** Apr 29, 2013 **Posts:** 203

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

To fix you gradient, try Filters>Noise>Spread and use a somewhat large value (100px or more).

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

This is weird. Color banding is so bad in your example - it hurts my eyes :mrgreen:

.
I can't reproduce it on 5Kx5K image. But I get exactly the same sort of 'ugliness'
if converted the image with applied gradient to Indexed.
Are you sure your image wasn't at some point converted to indexed (and then maybe back to RGB)?

P.S. Exporting image as .gif automatically converts image to indexed too (without warning you).

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

K1TesseraEna wrote:

This is weird. Color banding is so bad in your example - it hurts my eyes :mrgreen:

.
I can't reproduce it on 5Kx5K image. But I get exactly the same sort of 'ugliness'
if converted the image with applied gradient to Indexed.
Are you sure your image wasn't at some point converted to indexed (and then maybe back to RGB)?

P.S. Exporting image as .gif automatically converts image to indexed too (without warning you).

There are only 242 colors in the picture, and the histogram of the RGB channels a bit discretized, so this is likely.

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

ofnuts wrote:

There are only 242 colors in the picture, and the histogram of the RGB channels a bit discretized, so this is likely.

Here comes the verdict scientific proof :mrgreen:

btw, how do you determine the exact amount of colors in rgb image?

saulgoode · **Posted:** Tue Sep 02, 2014 2:12 am **(#10)**

K1TesseraEna wrote:

btw, how do you determine the exact amount of colors in rgb image?

"Colors->Info->Colorcube Analysis"

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

Thank you Saul

making use of the 'failed' gradient - recoloring image with
colors from active palette - pretty nice background, isn't it?

gmic>Aurora [hard to believe but there are only 32 unique colors in this one]

Zeo · **Joined:** Apr 29, 2013 **Posts:** 203

ofnuts wrote:

To fix you gradient, try Filters>Noise>Spread and use a somewhat large value (100px or more).

Oh yeah, I know there is filter somewhere in GimP that can deal with this kind if thing (I'm not using filter much) :yes

After using Filters>Noise>Spread (I use 1000px :hehe

........) and gaussian blur-it about 15 point and I got this kind of result that kinda good, at least normal eyes will not notice it (especially when resized) :

But, I do not recall changing mode to Indexed, but there are something interesting:
If I use 'darker' color the gradient/blend tool will work less noticeable (it's pure black in background)

But if I use 'lighter' color, same setting, the result will have some 'ugliness'

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

I see artifacts in both... the problem is that due to the 8-bit color depth, which restricts color channels to 256 values, you can have a line in the gradient where the RGB values 'jump' across the line. In which case even small jumps are visible. The spread noise makes the jump happen more randomly and makes it less visible (btw, by doing a blur after the spread noise you are recreating artifacts....).

Zeo · **Joined:** Apr 29, 2013 **Posts:** 203

Oh right, I set the noise value too high(1000px)... At 250 px seems enough and I don't need to use gaussian blur... :oops:

So that's 8-bit vs higher color depth, I think I have read about that somewhere... :oops: