Re: [Gimp-user] why would the input png automatically get blurred?

[Ofnuts <ofnuts gmx com>]

On 15/03/17 21:14, bsmile wrote:
> > The image is in indexed colors mode. Use Image > Mode to switch to
> > RGB.
> > It is a very fast way to create a new layer from exactly what's
> > visible
> > in the image as a whole. This is useful if you want to reuse the
> > current
> > result in another image, for example.
>
> Thanks, after change the mode, the figure can be corrected loaded. Can you
> please explain why? This surely helps quickly understand gimp.

In indexed mode, the color of a pixel in the image (in all layers) is 
taken from a "color map". Since the index in the color map is a 8-bit 
byte, you can only have 256 colors (across all layers). When you import 
another image, its colors are approximated with the 256 colors in the 
current colormap. The first victims of this color shortage are the 
anti-aliasing pixels along the edges of things that are a blend of the 
two colors in various (and numerous) proportions(*) and the edges become 
jagged.

(*) Experiment: Take a blank image, add a black text layer, and merge it 
down to obtain one single layer with black text over white. Then Go to 
Colors>Info>Color cubes analysis.  You will find much more than two 
colors... these are the 250 shades of grays used in the edge pixels. You 
can start Color>Posterize and see what happend to the text outline when 
you reduce the number of colors.