On 12/7/07, Igor Tandetnik <[EMAIL PROTECTED]> wrote: > P Kishor <[EMAIL PROTECTED]> wrote: > > folks, I have never worked with BLOBs, but am now going to. Feel a > > bit nervous. > > > > Here is a question -- what if I have a rather large image and I want > > only a certain part of it? Let me give an example -- say, I want to > > store an image of the entire US, but when I want to see only Hawaii, I > > ask SQLite to fetch the portion of the image with a certain bounding > > box, say, the rect of Hawaii. > > SQLite of course knows nothing about images. As far as it's concerned, > you are storing an array of bytes - it couldn't care less if it contains > image data or not. So you cannot directly ask it to retrieve a portion > of the image. >
well, I used image as an example because I was interested in image. I guess, the same logic could be applied to any other BLOB. > Recent versions of SQLite allow retrieving contiguous segments of the > BLOB, given an offest and length. If you store your image as an > uncompressed bitmap, then each scanline is stored as a contiguous > segment. Given a rectangle, you can retrieve each scanline of the > portion you are interested in, then compose them in memory into the > final image. Ahhh.... so this is the path to pursue. Good to know that. Now to find someone who has actually done that. :-) > > Having said that, SQL database is probably a wrong tool for image > manipulation. > You are correct. But I don't want to manipulate the image with SQLite (or any SQL db). I just want to store and retrieve it efficiently. Storing images as files certainly precludes being able to find just *that* particular rect and extract it out of a file. One would have to experiment with many image tile size, so on, so forth. Thinking of an image not as an image but as an array of bytes intuitively seems to be the right direction to be thinking in. Many thanks, Puneet. ----------------------------------------------------------------------------- To unsubscribe, send email to [EMAIL PROTECTED] -----------------------------------------------------------------------------
