Remarks: The above is possible because, unlike PNG, (i) only "index" is used to denote the transparent color, not the actual color value (otherwise one has to insert bytes) and (ii) there is no "checksum" involved. One by one loop through the frames, then dump back bytes to the file. of the wanted transparent color, then enter the index in the specific field (which is a Byte) accordingly. (2) Find out from the global or the local pallete entries (within the boundary of the No of global or the No of local entries as the case may be) what is the index No. Unfortunately no, the GIF format doesnt support partial (alpha-channel) transparency, meaning any pixel can only be fully tansparent or fully opaque, so its not possible to make partially transparent GIFs and achieve anti-aliasing effect against different backgrounds. (1) Change the frame's "use transparent color" flag to "Yes". If "Yes", nothing further to be done for this frame. Transparent loading GIF, SVG and APNG animation. Establish whether this frame is coded to "use transparent color". of local palette entries (will be of use). Establish whether a specific frame uses global palette, if it says "No", Local Pallete exists, obtain the No. In addition to SVG format, we also provide other formats including PNG, GIF and CSS for you to download, depending on the resource type you are working on. of global palette entries (will be of use) Images are all based on the loseless vector format SVG to optimize the image quality and file size. Ascertain whether Global Palette exists The answer is "Yes" on the premise that one is familiar with the GIF file structure, as the job will entail, e.g. If hImg 0 Then Call GdipDisposeImage(hImg)Ĭan we make the background of an animated gif transparent ?Ĭan we do that in VB without the use of an intermediary transparent container or third party libraries? Ret = GdipSaveImageToFile(hImg, StrConv(inFileSpec, vbUnicode), uCLSID, uEncParams) Ret = GdipSetImagePalette(hImg, VarPtr(mPalette)) If inTranspColor >= 0 And inTranspColor 0 Then GoTo earlyExit 'Since inDIB is created bottom up, vertically adjust inDIB Ret = GdipCreateBitmapFromHBITMAP(inDIB.DIBhDIB, 0, hImg) Optional inTranspColor As Long = -1) As Booleanĭim uEncParams As EncoderParameters 'Memo: We have pre-dimensioned its Parameter as "(1)" for convenience (The red dots around the transparent part are the result of the newly generated palette).Public Function SaveDIB_via_GDI_BPP8(inDIB As clsDIB, ByVal inFileSpec As String, ByVal inEncoder As GpImageFormat, _ Draw red text while preserving transparency:įfmpeg -y -i test.gif -filter_complex "drawtext=text='Test':fontcolor=red:fontsize=120,split palettegen=reserve_transparent=1 paletteuse" output.gif.Convert the PNG image to GIF image (with transparency):įfmpeg -y -i 6qepl.png -filter_complex "split palettegen=reserve_transparent=1 paletteuse" test.gif.Download the PNG image from my former post (image in RGBA format).(In theory, there is more efficient way doing it when the red color is part of the original palette, but I don't thing FFmpeg supports that kind of optimization). My guess is that FFmpeg decodes the GIF into raw RGBA format and draws the red text on the RGBA image (in the RAM).Īpplying split, palettegen and paletteuse, generates a new palette (ignoring the original palette), and convert the raw RGBA image to indexed image using the generated palette. Ffmpeg -y -i test.gif -filter_complex "drawtext=text='Test':fontcolor=red:fontsize=24,split palettegen=reserve_transparent=1 paletteuse" output.gif
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