[Qgis-user] Raster: replace a single value with another value

[Andreas Neumann]

Hi,

I have a very simple task (at least I thought it is simple), but am not 
able to do it properly.

I have a grayscale tiff value where I would like to replace the value of 
249 with 255 - all other values should stay as they are.

I tried with gdal "nearblack", but nothing changed - I started a 
separate email-thread about that at the gdal list.

Then I tried with the QGIS raster calculator - but it does not support 
conditional syntax.

I tried with Processing and GRASS - but it would stop at 8% - the file 
is quite big.

Finally I came across SAGA "Reclassify with grid value". The dialogue is 
very complicated and hard to understand. After a while it would stop 
with an error message telling me that Saga may not be properly 
configured - but it says that it is properly installed. Quite confusing 
...

I am trying on Win7 64bit.

If the file wouldn't be so big I would try this task in The Gimp - where 
it is very simple to replace one pixel values with another - using 
"Select by color" and "fill with a specific color".

Any idea how I could achieve my task with GDAL, QGIS, GRASS or Saga?

Thanks,
Andreas