How to create a brightness gradient?

[Andy_C]

Hi everyone, I'm trying to adjust the brightness across an image in Gimp (2.10) and I'd really appreciate your help. The original image (link below) is the front of a furniture cabinet where the room was lit from a window on the left of the cabinet - the image therefore has higher exposure on the left, and is darker on the right.

 
I'm trying to adjust the image to give a more even exposure across the image. I've seen various blog posts and YouTube videos that use the gradient tool to do this. They typically use the gradient tool to fade from a dark foreground colour to a transparency. I've tried this in various ways but unfortunately the part of the image where the foreground colour is applied does not look good - the colours, contrast, and detail become washed out by the foreground colour.
Here is an example of how it looks.

I've tried using a foreground colour that has a similar colour tone to the rest of the image (rather than just black or dark grey), but this doesn't improve the image much.
 
Is there a way to create a brightness gradient? i.e. brightness is reduced on one side of the image, and gradually increases to full transparency on the other side of the image?
 
I'm relatively new to Gimp, and I'd really appreciate your help!
 
Andy_C

[rich2005]

For a hands-on eyeball method.

Add a layer above.
Set the layer mode to Soft light 
Draw in a black-to-white gradient (left to right) very little on the black side.
Adjust the layer opacity to suit.

   

[Ofnuts]

IMHO mostly  a matter of contrast. A rather quick fix;

• Duplicate the layer
  
• On the copy, increase contrast until the left side looks like the right side of the original
  
• Add a layer mask
  
• On the mask, add a gradient white (left) to black (right) gradient
  
• While in the gradient tool, click on the line to add a "stop" and move it around to adjust the opacity change.
  

   

[Andy_C]

(09-14-2022, 02:03 PM)rich2005 Wrote: For a hands-on eyeball method.

Add a layer above.
Set the layer mode to Soft light 
Draw in a black-to-white gradient (left to right) very little on the black side.
Adjust the layer opacity to suit.

That's great, thanks @rich2005

---

(09-15-2022, 08:57 AM)Ofnuts Wrote: IMHO mostly  a matter of contrast. A rather quick fix;

• Duplicate the layer
  
• On the copy, increase contrast until the left side looks like the right side of the original
  
• Add a layer mask
  
• On the mask, add a gradient white (left) to black (right) gradient
  
• While in the gradient tool, click on the line to add a "stop" and move it around to adjust the opacity change.
  

Thanks @ofnuts!

[Krikor]

ok, sorry if I don't use the correct terminology.

IMHO, both the approach suggested by rich2005 and Ofnuts are about trying to adjust the luminosity, in order to even out the exposure on both sides.

The results obtained however, while balancing the exposure evenly, leave the right side of the image (the originally darker side) with a slightly more 'reddish' hue.

Maybe it's just my eyes...

So I tried to find a way to try to reduce this contrast in tone between the sides, and for that I used a mask to separate the sides, and I applied a curve to try to correct the difference in exposure and tone.
   

[Ofnuts]

(09-15-2022, 07:23 PM)Krikor Wrote: ok, sorry if I don't use the correct terminology.

IMHO, both the approach suggested by rich2005 and Ofnuts are about trying to adjust the luminosity, in order to even out the exposure on both sides.

The results obtained however, while balancing the exposure evenly, leave the right side of the image (the originally darker side) with a slightly more 'reddish' hue.

Maybe it's just my eyes...

So I tried to find a way to try to reduce this contrast in tone between the sides, and for that I used a mask to separate the sides, and I applied a curve to try to correct the difference in exposure and tone.

You didn't really try my method. I use two layers with a mask, the right side is left untouched. But it's true that there is a slight color shift (or at least desaturation) on the left, but this would require processing each color channel separately.