Sometimes when one want to use the gimp 'levels' pickers, black or white is in most cases easy to find on a photo.
Grey can be a problem (over the years...). One can find grey areas on a photo with this workflow :    
- load photo in gimp
- copy the layer (for compare with the corrected photo - always work on copy) (1)
- make a new layer and name it 'gray' 
- fill it with color gray (HTML notation : 808080 or CMYK notation : K=50) (2)
- set layer grey in mode 'Difference'
- make new layer 'New from Visible' (name layer = Visible) (3)
- On layer visible use  : Colours / Threshold
- move the slider to the left (layer becomes white) and move the slider back just to see just black areas (4)
- the black areas are the places where you can use the grey picker from the 'Colour / Levels'

If the result is not what one want, then use the different gimp colour tools to optimize. 
There are 4 different pictures on the screendump to illustrate the steps in the workflow. 
   

The attached image is the output of the Edge filter on a colour image. Wondering how I can get rid of the colour and keep the black edges only. Thanks.

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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

I'd like to create an image of the planets 3/4 submerged in water - like stepping stones.

I've used GIMP a little over the years but I'm not a GIMP expert. Any idea how I would go about creating such a scene? I think I'd like to start with something completely fake - such as fake water with 3 spheres inside the water and then map/blend planet or pebble texture over the top.

Sorry, I know this is a very high-level question - I just don't know where to start.. other than with a Youtube tutorial on creating fake sky reflecting water I guess.

Hi all,

I'm trying to figure out if there's an easier way to make selections that have a fixed width, but are at an angle, for comic book panels.

Currently I've been drawing panels following this old guide (http://gimpchat.com/viewtopic.php?f=23&t=9812). Basically, make a selection, then remove fixed height/width rectangle selections, and assigning the resulting selection to a path. It works great, but really only works in straight lines as far as I can tell.

It looks like I can make a fixed height/width selection using the rectangle select tool, and then go to the rotate tool, and change it to transform selections, I can make the angled rhombuses that I want. BUT - I can't rotate a selection that is being added or removed from a selection.

For example: I select my whole page. I draw a new selection, that is set to remove from the current selection. Once I draw it, I have the ability to edit it - make sure it's in the right position, make it a little bigger or smaller, etc. But if I try and click on the rotate tool, Gimp finishes the merge operation and only lets me rotate the new selection shape.

I could draw all of the angled rectangles separately, save them as paths, and then remove each one from my selection, but that seems very cumbersome and hard to work with since I can't see the other selection areas.

Is there a better way to do this? I wish I could just draw a rectangle selection and then rotate it before I commit to it right there.

Hello,
I would like to remove the greyish background from this scanned document. The difficulty is that this background is made up of pixels in different shades of grey, some of which are found in the elements to be kept. In this case, the colour selection tool does not give good results.
This is why I am looking for ideas on this forum. So thanks for any suggestions.

GT

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https://xkcd.com/2671

A so-called 'interspecies arms race' has broken out between humans and cockatoos in Australia.

It involves the cockatoos ability to open and raid plastic 'wheelie bins' used for rubbish.
Humans attempts to thwart the cockatoos has mixed results. Bricks don't work
Check-out the video.

Often when I switch to the free select tool, I find it has switched itself into intersect mode.  This appears to also be the case for the rectangle select tool.  This may be more of a general problem with tool options automatically changing over to the right most position, as the move tool is switching into path mode on it's own too.  I've tried setting them to the left most option, going into edit>preferences and saving the tool options.  It didn't help.  What could I be doing that would change the options on multiple tools that aren't selected?

When I import an image to an existing image as a new layer many times the color red is brought in as gray.  I have changed my preferences and color management many times but nothing seems to work.  How do I get the image to come in true?