I would like to know how does microsoft word transforms and saves various image formats inside doc/docx format?
For docx, we can easily look inside and see inside ~\media folder.
What is seen is that if we insert an image using "Insert -> Picture", various image formats like bmp, gif, tiff etc. seem to get converted to png and stored like one for Word 2007 (docx). Same is the case with binary (97-2003) format (doc).
Is it possible to include the image in document in its original format like bmp, gif, tiff etc.?
It looks to me that Word is converting some image types to a more compact storage option. PNG format was created to improve compression from GIF. BMP images have little or no compression. The conversion to PNG seems like a good choice.
I don't see any way to select the stored image format within Microsoft Word. The document specification indicates that the following image types can be stored: GIF, PNG, TIFF, PICT and JPEG. It also mentions that only PNG and JPEG should be used for interoperability.
My understanding from that information is that Microsoft Word will only store images in PNG or JPEG formats. If you create the document using OpenXML, then you can store the other formats. I don't know if Microsoft Word will convert those existing image types in a document whenever it is saved or not.
Generally 3 image formats are kept inside of Office documents - JPEG, PNG and WDP (en.wikipedia.org/.../HD_Photo) in 2010 client-created documents. The WDP one is kept as a hi-res JPEG-type original, not actually shown in the document, but is used when newer 2010 features are applied to images, such as "Remove Background". The "removed background" image will be rendered as a separate PNG (again, with the WDP original remaining in the package). All other images are converted to PNG when imported. The document's thumbnail that allows it to be previewed in places like Windows Explorer is saved as a JPEG (if you chose to save a thumbnail).
It's totally possible to have/keep an image in its original format for most image types (TIFF, GIF, etc.), but only if they are inserted sans-client (such as programmatically or through opening the OPC package and manually adding them and their relationships, etc.), but as soon as that manually-edited document is opened in the Word client and saved, they will be converted to PNG.
Thanks bobm and Todd for you replies. It was helpful.