##Input_raster1=raster
##Band_raster1=output raster
from qgis.core import *
from qgis.gui import *
from qgis.utils import iface
from PyQt4.QtCore import *
from PyQt4.QtGui import *
import os
from osgeo.gdalconst import *
import numpy
import sys
import osr
driver = gdal.GetDriverByName("GTiff")
ds = gdal.Open(Input_raster1, GA_ReadOnly)
dst_ds_red = driver.Create(Band_raster1, ds.RasterXSize, ds.RasterYSize, 1, GDT_Float32)
dst_ds_red.SetProjection( ds.GetProjection())
geotransform = ds.GetGeoTransform()
if not geotransform is None:
  st_ds_red.SetGeoTransform( geotransform )

bandList = []
band = ds.GetRasterBand(2)
data = band.ReadAsArray()
bandList.append(data)

rasterlayer_red = numpy.zeros((ds.RasterYSize, ds.RasterXSize), dtype=numpy.float32)
for i in range (0, ds.RasterXSize):
  for j in range (0, ds.RasterYSize):

    RED = (float(bandList[0][j][i]))
    rasterlayer_red[j][i] = RED
dst_ds_red.GetRasterBand(1).WriteArray(rasterlayer_red)

##Input_raster1=raster
##Band_raster1=folder
from qgis.core import *
from qgis.gui import *
from qgis.utils import iface
from PyQt4.QtCore import *
from PyQt4.QtGui import *
import os
from osgeo.gdalconst import *
import numpy
import sys
import osr
driver = gdal.GetDriverByName("GTiff")
ds = gdal.Open(Input_raster1, GA_ReadOnly)
# Get filename of input raster
result = os.path.splitext(os.path.basename(Input_raster1))[0] + "_new.tif"
dst_ds_red = driver.Create(Band_raster1 + "/" + result, ds.RasterXSize, ds.RasterYSize, 1, GDT_Float32)
dst_ds_red.SetProjection( ds.GetProjection())
geotransform = ds.GetGeoTransform()
if not geotransform is None:
  st_ds_red.SetGeoTransform( geotransform )
...

import os
in_rast = r"in_raster.tif" # input path

# Next you can split the file extension from the file name
in_parts = os.path.splitext(in_rast)

# continuing from above

new_name = in_parts[0] + '_new' # in_raster_new
new_path = new_name + in_parts[1] # in_raster_new.tif

new_ext = '.png' # note the period is included
new_name = in_parts[0] + '_new' # in_raster_new
new_path = new_name + new_ext # in_raster_new.png