Re: [Gimp-user] why autocrop layer would not cut all the blanks?

[Ofnuts <ofnuts gmx com>]

On 16/03/17 00:22, bsmile wrote:
> > 1) Image>Autocrop image, once you have fixed 2) on the two layers.
> >
> > 2) You white background is not uniform it contains pixels with 253
> > instead of 255,
> >
> > http://imgur.com/zHn0KH9
> >
> > ... and autocrop only works with completely uniform backgrounds. You
> > can
> > fix this with "Levels", dragging the right hand of "Input" towards
> > value
> > 250 (or anything left of the line at value 253 in the histogram).
>
> Thanks for the explanation, but please be more specific where to locate the
> option of value to be revised?
>
> I right clicked my mouse to bring up colors->levels->input levels, output level,
> I changed the value to 250, and then ok, then layer->autocrop layer, but no
> difference, I right click my mouse again to input levels, it is still 255, like
> never been modified before.
If you use Windows>Dockable dialogs>Histogram the right of the histogram 
has two vertical lines, which indicate that that you have pixels with 
value 253 as well as pixels with value 255. You should also see these 
two lines in the histogram shown in the Levels tool. In Levels, if you 
drag the right handle of the input (top bar) to the left of the two 
lines (around 250), then everything bigger that the indicated value 
becomes pure white, so this should change your pixels with value 253 to 
pure white.