Scaling Images Before Digital Watermarking
I recently was forwarded a tech support call from Lori, our resident customer support guru here at Digimarc. She informed me one of our Digimarc for Images (DFI) Professional customers was having an issue with the watermark disappearing and asked me to help him out. In the 9 plus years I’ve worked for Digimarc, I’ve been called on to help out various professional and enterprise customers. I’ve done it often enough that I sort of go into autopilot mode and shoot out an email or call them back with an answer. However, this time I stopped myself. I thought, “Why not include this as a post on our new blog? I’m sure Sam isn’t the only one this has happened to.” So that is just what I’m going to do. Hopefully this information will be helpful for you. Sam – by the way, did receive a phone call and his problem is solved.
Sam is using a site that allows him to post his images to get feedback. The site lets him upload large images and then creates 4 smaller sizes for viewing. Sam noticed that some of the smaller versions of his images were not holding his watermark. Since he is looking for the best images to send to a publication he wants feedback, but doesn’t want someone downloading and claiming his image as theirs.
And now for the answer...
The DFI watermark has been tested to work reliably on images that have been scaled from 60% to 200%. While some images can ‘hold’ the watermark over greater extremes, there is a limit. Some of Sam’s images are 4000 x 3000 pixels and are watermarked at that size. When the review site scales down his images to 1600 x 1024, 1280 x 1024, 1024 x 768, 800 x 600 all of these sizes are below the 50% recommendation, the 800 x 600 size is only 20% of the original size. When I got in touch with Sam, who has been a customer for a number of years, he’d remembered the scaling requirements. He had already decided that he would be watermarking and uploading smaller 1024 x 768 versions of his photos.
Now when the reviewing site he creates the 800 x 600 version the watermark is still readable and can even survive additional scaling. Information regarding the best policies for how to watermark an image like this is in the digital watermarking guide on our website: https://www.digimarc.com/mypicturemarc/support/watermark-guide.asp
I’m going to continue to use this blog as a vehicle to distribute such tips and tricks. I encourage you to sign up for our RSS feed or provide us with your email to be automatically notified when my colleagues or I add a new post. It’s as easy as that. Also if you find I’m not answering the big question you have, don’t get mad – just use the Ask the Expert link on the right to submit your question. I’ll been informed – since I’m the expert who will be handling these questions. I’ll do my best to live up to the “expert” thing.
Thanks for taking the time.