Hi and sorry about the noobness of this question, I am fairly new to C and VIPS.

I am successfully using libvips in a VS2017 C++ project to load thumbnails from files on disk, using the C API. Its so FAST compared to the existing opencv implementation! Thanks for the great library.

My questions are several:

1) Existing code requires 640 x 640 thumbnails, I am currently using code like this:
vips_thumbnail(FileName, &out, 640)
which gets me nearly what I need except that only the longest axis is 640, I need to supply the image data letterboxed (or pillarboxed) ie. so that it fills the whole 640 x 640 but centered and maintaining aspect ratio. I saw a weserv enhancement discussing this weserv/images#80 (comment) but I couldn't find if this has been implemented in libvips or in the thumbnailer. If not is there another fast way?

2) Theres probably an obvious answer but I could not find how to directly access the image data in the VipsImage object. The documentation description of VipsImage states that "VIPS images are three-dimensional arrays, the dimensions being width, height and bands" but I cant find examples that show how to iterate through the data, the closest I could find is a region example here which I dont know how to transmogrify so it works with an VipsImage. Is there an example of this somewhere?

3) I want to use libvips to do what an existing block of opencv code does using a cv::Mat. It iterates through the (BGR) pixel data to build a new array organized like this :

• All R pixel data, followed by all G pixel data, then B pixel data.
• Pixel values are changed (from uchar) to floats with values from 0 to 1
  (It is formatted like this for feeding to a neural network)

At first I thought I would do the transformation manually like the original code but I have seen some really powerful code snippets like this and it occurs that libvips might already have the tools to reformat the data the way I need it. Is there any inbuilt functionality to do that?

Thanks for any advice!