in src/main/java/org/apache/sling/thumbnails/internal/DynamicTransformServlet.java [143:149]
private ByteArrayOutputStream transform(Resource resource, SlingHttpServletResponse response, String format,
Transformation transformation) throws IOException {
ByteArrayOutputStream baos = new ByteArrayOutputStream();
transformer.transform(resource, transformation, OutputFileFormat.valueOf(format.toUpperCase()), baos);
IOUtils.copy(new ByteArrayInputStream(baos.toByteArray()), response.getOutputStream());
return baos;
}