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TJvDBImage is a good component that support several picture formats. In JvJVCLUtils, it mentioned that the supported format can be expanded by RegisterGraphicSignature procedure. In the comment it mentioned :

WHAT IT IS:
   These are helper functions to register graphic formats than can
   later be recognized from a stream, thus allowing to rely on the actual
   content of a file rather than from its filename extension.
   This is used in TJvDBImage and TJvImage.

IMAGE FORMATS:
   The implementation is simple: Just register image signatures with
   RegisterGraphicSignature procedure and the methods takes care
   of the correct instantiation of the TGraphic object. The signatures
   register at unit's initialization are: BMP, WMF, EMF, ICO, JPG.
   If you got some other image library (such as GIF, PCX, TIFF, ANI or PNG),
   just register the signature:

     RegisterGraphicSignature(<string value>, <offset>, <class>)

     or

     RegisterGraphicSignature([<byte values>], <offset>, <class>)

   This means:
     When <string value> (or byte values) found at <offset> the graphic
     class to use is <class>

   For example (actual code of the initialization section):

     RegisterGraphicSignature([$D7, $CD], 0, TMetaFile); // WMF
     RegisterGraphicSignature([1, 0], 0, TMetaFile);     // EMF
     RegisterGraphicSignature('JFIF', 6, TJPEGImage);

   You can also unregister signature. IF you want use TGIFImage instead of
   TJvGIFImage, you can unregister with:

     UnregisterGraphicSignature('GIF', 0);

     or just

     UnregisterGraphicSignature(TJvGIFImage); // must add JvGIF unit in uses clause

   then:
     RegisterGraphicSignature('GIF', 0, TGIFImage); // must add GIFImage to uses clause

I follow the instruction and Added GIFImage in the uses clause at that unit. Also, in procedure GraphicSignaturesNeeded I added :

RegisterGraphicSignature('GIF', 0, TGIFImage);
RegisterGraphicSignature([$4D, $4d, 0, $2A], 0, TWICImage); // TIFF
RegisterGraphicSignature([$49, $49, $2A, 0], 0, TWICImage); // TIFF

The TIFF info is based on Tip: detecting graphic formats

Then I used the makemodified.bat to re-compile JVCL.

Before the change, loading image to the TJvDBImage will load the file and give endless error of "bitmap image not valid". After change, it refuse to load the file and give the same error for 1 time.

If I load GIF / TIFF image to the field using other tools, when displaying , it give endless error mentioned above. If I load the field content using the above link functions, it can display in a TImage perfectly.

So, what have I missed or doing wrong?

Thank you!

Justmade
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    Why are you recompiling JVCL? It doesn't look like you need to do that. – David Heffernan Mar 23 '12 at 12:47
  • @DavidHeffernan Yes, I can add the RegisterGraphicSignature to all my projects. I prefer directly modify the GraphicSignaturesNeeded procedure of JvJVCLUtils, where all the other RegisterGraphicSignature located. It centralize the format support registration. As I changed the JVCL source file, I need to re-compile it. I had did that quite many times when I modify other parts of JVCL and that should not be a cause of problem, I think. – Justmade Mar 23 '12 at 12:59
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    Still unnecessary. Your own unit's INITIALIZATION clause can call the registration function without modifying JVCL's units. So, when you download a new JVCL version, you will have to reapply your changes. You're starting down a road of pain. Not as bad as modifying the VCL itself, but still, needless pain. – Warren P Mar 23 '12 at 17:59
  • @WarrenP I agree that modifying JVCL is not necessary in this case. However, at lease it should do the registration same as putting them in my own units? So it is not the focus of the question. The focus is why registering them only change the TJvDBImage from load the file and report invalid on display to report invalid bitmap on load. Why it still cannot support the image formats. – Justmade Mar 23 '12 at 22:52

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