With Filters>Blur>Selective Gaussian blur, radius around 60 on your image:
Notice that it blurred out the diagonal lines, but hardly blurred the barcode, your red circle, or the checkerboard pattern.
Caution: this is fairly CPU intensive, wait for it to finish before pronouncing it dead:)
Use the Magic Wand (Fuzzy Select Tool) to select blocks of colour. You may need to adjust the threshold in the Tool Options to get a good selection
Then sample the colour you want using the Eyedropper tool
Do Edit > Fill with FG colour.
Repeat for different areas of the image.
If there are areas that can't be easily selected you may need to use the ...
You can "enhance" pixels that aren't there. There's practically nothing to work with. The best you can do is bump up the contrast, maybe put a High pass layers to condense the pixels. Beyond that, I'd say it's a lost cause.
In photo editors such as GIMP or Photoshop you can apply Curves to increase the contrast:
This is from Photoshop, but GIMP has the exact equivalent.
Then you can flip the image horizontally to remove the mirrored effect:
As you see you can read a word and maybe even occasional sentences from here and there, even if all letters are not well visible. In ...
With the Curves tool:
Set to "Freehand"
With the pen that appears, draw a line along the bottom edge (you can even stay a bit below) from the left corner up to the threshold value, to make a step in the diagonal.
Open both XCF files.
In the XCF with the layer group, click and drag the layer group from the layers panel onto the other image tab along the top (do not release the mouse button).
When the other document window opens, drop the layer group onto the image window.
Unfortunately I can't do a screen recording of this to show you, since my screen recording ...
Next time you wanna add effects to GIMP layers consider one of the follwing techniques to be able to control them:
Layer backup: In this technique you create a duplicate layer from the original one and do all your effects on it. And you should hide the original one and name it like this:
Filters group: In this technique you would ...
You can at first make bad quality lens like color fringes by moving the R and G channels a little apart from the blue channel. Select all. Then select in the Channels panel one channel and move it few pixels to some direction. Select another channel and move it a few pixels to another direction. This was originally a good quality news photo. Moving the ...
Use the Rectangle Select tool to make a selection, then change the position or size by typing in the values you want in the Tool Options.
If you can't see the tool options, click Windows > Dockable Dialogs > Tool Options
There is. For some inexplicable reason it is hidden inside the 'Dynamics' options, whose help page is here. One of the preset dynamics you can select is 'Color From Gradient', and it does exactly what the 2.2 dialog describes with a slightly different UI.
You can accomplish such a task in a lot of ways in Gimp (even if I'd prefer to use ImageJ or ImageMagick to play with pixel values), for example using the Level tool or the Select By Color tool.
A quick way is select all the pixels within the range you are interested and fill them with black.
Starting from the original image:
You can use Select By Color ...
Copy or cut the layer you want to become the mask content (via Ctrl+c or the menu entry), then create the layer group mask, then paste and anchor the resulting floating selection, which will then go to the active layer mask.
No but you can choose to sample visible layers when using the Healing Tool.
From Gimp 3.13. Heal
If you enable this option, healing is not calculated only from the
values of the active layer, but from all visible layers.
If you want to heal only those 2 layers, you can try turning off layers that you do not want to change.
You can use Colors > Components > Mono Mixer to convert other than yellow to black and yellow to white:
You must decide how much orange can be accepted. In the next mix less orange has passed through:
If it must be yellow you can colorize the image:
In Gimp 2.10:
Paint the lines on a transparent layer:
Set the bucket-fill tool mode to Behind (selector at top of Tool options) and the
"affected areas" to Fill by line art detection.
Then click in the middle of the area to paint.
Yes, there are several possible ways to mitigate this problem which is caused by anti-aliasing. Here's one fairly simple method.
On a new transparent layer. Draw shapes as you normally would, with the Paint Brush tool set to black, to get nice smooth hand drawn lines.
Create a new transparent layer under that. Select the bucket tool and choose a foreground ...
Your black edges are blurry. They have partially transparent or partially with background mixed pixels. That's used commonly for anti-aliasing i.e. to avoid jaggy look and it comes without asking if you scale objects or use drawing tools without preventing anti-aliasing.
When you draw with so low resolution that pixels can be seen you very likely expect ...