GDI+ Jpeg Save Quality

[Philip Zeller]

I've observed that the default jpg save quality using GDI+'s GdipSaveImageToFile leaves something to be desired. No trouble, I thought, I'll just adjust the quality.

I've got code to demonstrate the problem. The program is very long, but I believe I've enclosed enough code to show all relevant portions...

From the top, Types:

TYPE EncoderParameter
    pGuid AS GUID
    NumberOfValues AS DWORD
    dwType AS DWORD
    Value AS DWORD
END TYPE

TYPE EncoderParameters
    pCount AS DWORD
    Parameter(0) AS EncoderParameter
END TYPE

A couple of constants I'm using:

$EncoderQuality = GUID$("{1D5BE4B5-FA4A-452D-9CDD-5DB35105E7EB}")
%EncoderParameterValueTypeLong = 4

And finally, the code in question, which crashes on "...has encountered a problem..."

    DIM eps AS EncoderParameters
    eps.pCount = 1
    eps.Parameter(0).pGuid = $EncoderQuality
    eps.Parameter(0).dwType = %EncoderParameterValueTypeLong
    eps.Parameter(0).NumberOfValues = 1
    dwQuality& = 85
    eps.Parameter(0).Value = VARPTR(dwQuality&)

    r& = GdipSaveImageToFile(img, FileSpec, sEncoderClsid, eps)

Now, I know my img, fileSpec, sEncloderClsid are okay. In fact, this works perfectly well if I do either one of the following:
1. Drop the eps reference alltogether when calling GDIpSaveImageToFile or;
2. Change eps.pCount = 0

This tells me that there is something wrong with what I am putting into the eps structure. Thus, whatever is wrong must be in the above lines of code.

Any thoughts?

[José Roca]

I think that you are filling the UDT correctly, but can you let us know which DECLARE are you using for GdipSaveImageToFile?

[Philip Zeller]

DECLARE FUNCTION GdipSaveImageToFile         LIB "gdiplus.dll" ALIAS "GdipSaveImageToFile"         (BYVAL lpImage AS DWORD, BYVAL flname AS STRING, clsidEncoder AS GUID, OPT BYVAL EncoderParams AS encoderParameters) AS LONG

[José Roca]

Change it to

DECLARE FUNCTION GdipSaveImageToFile         LIB "gdiplus.dll" ALIAS "GdipSaveImageToFile"         (BYVAL lpImage AS DWORD, BYVAL flname AS STRING, clsidEncoder AS GUID, BYREF EncoderParams AS encoderParameters) AS LONG

[Philip Zeller]

Perfect

Perfect solution, didn't think of that DECLARE not passing byref.

Of course, things are always plain as day in hindsight.

Thanks!