The fill tool The tool that you will use to isloate objects in your picturedialog works with a thread walking the original picture and adding pixels that meet the criteria that you set up. The tread start directly as the dialog pops up. You may stop the thread at any time by pressing the Stop button. The thread stops automatically when no more pixels that meet the criteria can be found.
If you do not get the desired results you can click one of the "Suggest" buttons. the "7x7 pixels" button analyze a 7 by 7 pixel neighbourhood of the point where originally clicked and calculates settings from that... "21x21 pixels" does the same but uses a bigger area... So if you get to few pixels in your image part, click a higher "suggest" button. If you get to much click a lower value.
If you see the image part An Image that you have produced with the Fill tool and that you can change the channels of the HSV color space in. that is being produced by the picture-walker-thread is not any good, you can stop the thread, if it has not stopped by itself already, and go to the settings tab, by clicking the tab or by clicking the advanced button.
In the settings tab you set up the rules that the thread uses to decide if a pixel is valid for the image part or not.
Three basic rules exists; Hue The color without respect to saturation and lightness rule, Saturation The amount of white mixed in to the color rule, and Value rule. You may tick the checkboxes to use any or all of the rules. The rules work with a percent deviation of the starting point value. In the colored bands below each slider you see what the colors that meet the criteria looks like.
There are also two additional setting that effect the criteria; Compare to neighbour and Use 9 value average.
The Compare to neighbour rule makes the thread compare the pixel it worked with last to the possible pixels next to it, rather than comparing the possible pixels to the original pixel you clicked. This setting works best if your object is very different from the absolute surrounding.
The Use 9 point average rule makes the thread take an average of the neighbourhood of each possible pixel before testing the criteria. This setting is good when you have a speckled background.
When you have made alterations to the rules you can press the Restart button to start the thread again.
When the thread is finished you can press the Add this button or Cancel. Cancel will discard your result, and the Add this button will add the result as a new Image part in the image part grid.