How to fix wavy surface

[WuYuFeng]

Greeting! The surface of the object in the original photo is wavy.  Please see the attached. I would like to seek your advice on how to smoothen such surfaces while maintaining texture and look-and-feel.

Thank you for your help, have a good day!

[rich2005]

Can you be more explicit and indicate which part of the image you consider "wavy". Looks normal to me.

[WuYuFeng]

Thank you Rich for your reply. I am referring to the black surface that looks uneven.

[PixLab]

My first thought would be the dodge and burn tool
or this tuto
https://www.youtube.com/watch?v=sRMFYKiXB6U

[rich2005]

It is that shading which give the image a bit of shape. You could replace the whole of the textured area with a new pattern. It will look flat.
The attached 01-fabric.png goes in your Gimp textures folder (wherever that is in MacOS) . Made using a Gimp plugin resynthesizer as a seamless image.
Make a selection. Fill with the pattern. Add a shadow to give a bit of shape.

A 40 second example https://i.imgur.com/zhTj27o.mp4 you have the time to be a bit more accurate.

[Ofnuts]

The wavy aspect is likely a moiré pattern (as are the vertical darker stripes). This happens because the spacial frequency of the fabric is close to the spacial frequency of the sensor (in other works, threads in the fabric almost match pixels (or a multiple) in the sensor).  

Normally best avoided at shoot time:

• by shooting closer or farther to change the spatial frequency of the fabric on the sensor
  
• by blurring the picture a bit (focus blur, or the oold nylon-hose-over-the-lens trick)
  
• by taking two to four picture with slighly different positions (which will display the moire pattern a lot), then aligning them and blending them with a median filter, average filter, or "lighten/darkenen" only blend mode.
  
• if you shoot raw, you demosaiciing algorithm can have tweaks to suppress moiré (or you can have the choice between several algorithms, more or less prone to moiré).
  

In Gimp, a solution to mitigate the problem.

• Filters ➤ Enhance ➤ Wavelet decompose
  
• Inspection of the result shows that the problem is mostly in the Scale 6 and Scale 7 layers:
  

   

• In these two layers, sample the color in that area (with a large sample average radius), and use a soft brush to repaint the problem areas to make them more uniform.
  

   

[WuYuFeng]

(07-25-2021, 11:29 AM)rich2005 Wrote: It is that shading which give the image a bit of shape. You could replace the whole of the textured area with a new pattern. It will look flat.
The attached 01-fabric.png goes in your Gimp textures folder (wherever that is in MacOS) . Made using a Gimp plugin resynthesizer as a seamless image.
Make a selection. Fill with the pattern. Add a shadow to give a bit of shape.

A 40 second example https://i.imgur.com/zhTj27o.mp4 you have the time to be a bit more accurate.

Thank you Rich, this is very helpful.

[PixLab]

(07-25-2021, 11:29 AM)rich2005 Wrote: Made using a Gimp plugin resynthesizer as a seamless image.

OK, I was very interested in that part... I did some trial and errors
But I found how you did it.

I first tried and got only "garbage", I mean not what I was searching for
like this > select a "clean" part of that bag > copy > paste to have it the clipboard > Edit > Fill with pattern seamless... > select that new pattern = garbage

Then after 2 or 3 trial, and knowing that Resynthesizer is spread in many parts in the menu, I started searching for it (/) ...
So successful try was > Filters > Map > Resynthesize

Is it the way you did it?