#263 Failure writing GIF

[Mathew Maher]

Performing back-to-back write/read tests through the library, writing a FIF_GIF creates a corrupt file. Upon attempted readback, the error "EOF reading Logical Screen Descriptor" is thrown.

format = FIT_BITMAP
BPP = 24;
(all local code checked out by reading/writing to other formats).

[Hervé Drolon]

Hi,

First, note that the GIF format does not support 24-bit formats.
You should see an error message when using FreeImage_SetOutputMessage and FreeImage_Save should return NULL.

Now I don't understand how you managed to save a 24-bit dib as GIF using FreeImage (note: your sample file is not a GIF file, just edit it with a text editor to see this).

Can you show me a sample code ?

Hervé

[Mathew Maher]

Hi Herve,
Thanks for the fast response on this!

Apologies for the muck-up: I made the assumption 8bits meant 8bits per channel (x3 = 24bit)!

To get to the point of saving, I did:

a). FreeImage_AllocateT(FIF_BITMAP, x, y, 24);
b). used FreeImage_GetBits() to populate bitmap ([FI_RGBA_RED], etc)
c). performed the following write function:

bool ImageWriter(FIBITMAP bmp, const char lpszPathName, FIF_GIF,GIF_DEFAULT)
{
FREE_IMAGE_TYPE itype = FreeImage_GetImageType(bmp);

if (!bmp)
    return false;

//if no output type specified, try to guess it from the filename extension
if (fif == FIF_UNKNOWN)
{
    fif = FreeImage_GetFIFFromFilename(lpszPathName);
}

// check that the plugin has sufficient writing and export capabilities ... 
if ((FreeImage_FIFSupportsWriting(fif)) && (FreeImage_FIFSupportsExportType(fif, itype)))
{
    //everything good, save it! 
    if (FreeImage_Save(fif, bmp, lpszPathName, flag) == TRUE)
        return true;
}

return false;

}

The writer returns true.

Let me know if you need any more detail.

cheers, and thanks for your hard work!

Mat

[Hervé Drolon]

Hi,

The correct test should be someting like this

BOOL fipImage::save(const char* lpszPathName, int flag) const {
    FREE_IMAGE_FORMAT fif = FIF_UNKNOWN;
    BOOL bSuccess = FALSE;

    // Try to guess the file format from the file extension
    fif = FreeImage_GetFIFFromFilename(lpszPathName);
    if(fif != FIF_UNKNOWN ) {
        // Check that the dib can be saved in this format
        BOOL bCanSave;

        FREE_IMAGE_TYPE image_type = FreeImage_GetImageType(_dib);
        if(image_type == FIT_BITMAP) {
            // standard bitmap type
            WORD bpp = FreeImage_GetBPP(_dib);
            bCanSave = (FreeImage_FIFSupportsWriting(fif) && FreeImage_FIFSupportsExportBPP(fif, bpp));
        } else {
            // special bitmap type
            bCanSave = FreeImage_FIFSupportsExportType(fif, image_type);
        }

        if(bCanSave) {
            bSuccess = FreeImage_Save(fif, _dib, lpszPathName, flag);
            return bSuccess;
        }
    }
    return bSuccess;
}

See also FreeImage_FIFSupportsWriting in the PDF doc.

Hervé

[Hervé Drolon]

Closed in release 3.18.0
Please open a new bug if your problem persist.