.NET Framework - Base64 and .gif

Asked By Jsimpson

26-Oct-08 07:07 AM

I am working with encodeing and decodeing image strings to base64.

My.Types.ps1xml

[System.Convert]::ToBase64String([System.Text.Encoding]::UNICODE.GetBytes($this))

[System.Text.Encoding]::UNICODE.GetString([System.Convert]::FromBase64String($this))

Update-TypeData c:\scripts\My.Types.ps1xml

$pic = Get-Content "c:\scripts\test.bmp"
$pice = $pic.ToBase64String

This works great.  I can unencode it and save it as a file of a
different name and all is well. Where I run into problems, is if I do
the same with a gif file

$gif = Get-Content "c:\scripts\test.gif"
$gife = $pic.ToBase64String

$gife is empty.  Doing a GM on both says they are System.String and
have all the same methods and properties includeing ToBase64String and
FromBase64String, but it doesn't work.  Anyone know what I am
missing?  The eventual goal is to be able to take a base64 encoded gif
strin from a XML response and save it as a gif file.

Thanks,
JSimpson

26-Oct-08 07:07 AM

($=ADthis))
in=ADg($this))

So I decided to cast the get-content variable as a sting.

[Sting]$gif =3D Get-Content "c:\scripts\test.gif"
$gife =3D $pic.ToBase64String

That seemed to work, but when I send it back to a file

$gife.FromBase64String | Set-Content "c:\scripts\LOGO_S2.gif"

It seams to work, but the image comes out scrambled.  It must have
something to do with the internal formating of a gif, but I am not
sure what....

JSimpson

24-Oct-08 04:26 PM

Convert the image's bytes directly into a base64 string, then, to create the
new image file convert the base64 string back to bytes and pass them to
Set-Content's -Value parameter, be sure to use Byte encoding.
To get the byte array from the image file call [io.file]'s ReadAllBytes
method or use Get-Content and set its -Encoding parameter to Byte,
[io.file]'s ReadAllBytes method is much faster.

$byteArr = [io.file]::readAllBytes($file)
$byteArr = gc $file -en byte

$file = 'c:\scripts\test.gif'                                # fullpath
$encStr = [convert]::toBase64String([io.file]::readAllBytes($file))
sc c:\test.gif ([convert]::fromBase64String($encStr)) -en byte
ii c:\test.gif
sleep -m 250
ri c:\test.gif

--
Kiron

01-Nov-08 06:57 AM

($=ADthis))
in=ADg($this))

Just a comment on the naming: I would expect ToBase64String to be a
(script)method because of the commonly used prefix "To." If you're
intent on using a (script)property, maybe rename it to

- Oisin

01-Nov-08 06:57 AM

On Oct 26, 2:21=A0pm, "Oisin (x0n) Grehan [MVP]" <ois...@gmail.com>
es($=AD=ADthis))
trin=AD=ADg($this))
f

I actually gave up and did it with .net like this...

[void][reflection.assembly]::LoadWithPartialName("System.IO")
[Reflection.Assembly]::LoadWithPartialName('System.Drawing')

$pic =3D $xml.image.gif

$byte =3D [System.Convert]::FromBase64String("$pic")

$memoryStream =3D new-object System.IO.MemoryStream
$memoryStream.write($byte,0,$byte.Length)

$img=3D[Drawing.Image]::FromStream($memoryStream, 'Gif')

$img.Save("c:\scripts\pic.gif", 'Gif')

$img.Dispose()

I don't remember where I found it, but it works.  :)

Thanks for all the help.

JSimpson