Question

In Google AppEngine I want to transform a boolean[] into an image then serve the image. I want the boolean[] to be transformed to black and white pixels. I can see that AppEngine provides

import com.google.appengine.api.images.Image;
import com.google.appengine.api.images.ImagesService;
import com.google.appengine.api.images.ImagesServiceFactory;

// ...
byte[] imageData;  // ...   
ImagesService imagesService = ImagesServiceFactory.getImagesService();    
Image image = ImagesServiceFactory.makeImage(imageData);

but I don’t know what the format of the byte[] imageData should be, i.e., how to transform the boolean[] to byte[]

And once I have this image, how can the client get it?

Answer 1

The Image service API accepts data in any of the supported image file formats. According to this page, these formats include “JPEG, PNG, WEBP, GIF (including animated GIF), BMP, TIFF and ICO”. The Image service does not provide a way to create new image data from scratch. But you can use a graphics library to produce the image in one of the accepted data formats, then use the service to convert it to another format, or transform it. Of course, depending on the graphics library, you may be able to get the final image directly from the library, and not use the service.

To serve an image, just set the appropriate Content-Type header for the data format you’re using, then write the bytes of the image data to the response’s output stream:

// byte[] pngData = ...
resp.addHeader("Content-Type", "image/png");
resp.getOutputStream().write(pngData);

If you want to try generating the image data without a library, the BMP format might be easiest. You can use the Images service to convert this to PNG.