Converting surfaces to display depth results in slower speeds! Also slower with SDL_SetAlpha!

Dear SDL affectionados,

I have the following function which is called whenever I load an SDL
image called LoadImage. Basically, this uses SDL_IMAGE to load an image
and return the pointer. I then pass this new surface pointer to
OptimizeImage, which converts the image to the display depth. However,
when I do so it is often slower by a considerable margin. This is with
the latest .10 release of SDL. Can someone tell me why this might occur?

Function LoadImage:Byte Ptr( file:String , blend:Int )
    Local img:Byte Ptr = IMG_Load( file )
    img = OptimizeImage( img , blend )
    Return img
End Function

Function OptimizeImage:Byte Ptr(image:Byte Ptr,mode:Int)
    Select mode
        Case ALPHABLEND 'Convert with all the trimmings
            Local tempImage:Byte Ptr = SDL_DisplayFormatAlpha(image)
            Return tempImage
        Case MASKBLEND 'Convert with solid

            Local tempImage:Byte Ptr = SDL_DisplayFormat(image)
            Return tempImage
        Case SOLIDBLEND 'Convert with solid
            Local tempImage:Byte Ptr = SDL_DisplayFormat(image)
            Return tempImage
    End Select

(note: SetBlend often slows things down too. I took Gabriel Gambetta’s
advice to call SDL_SetAlpha before drawing but that slows stuff down too!)

Function SetBlend ( image:Byte Ptr , mode:Int )
    If mode = ALPHABLEND
        SDL_SetAlpha( image , SDL_SRCALPHA | SDL_RLEACCEL , 255)
        SDL_SetAlpha( image , SDL_RLEACCEL , 255)   
End Function