These best practices will help ensure your Digimarc® Discover watermark can be easily read in your printed materials.
We have designed our Online Services Portal (OSP) to be easy-to-use and accessible to most skill levels. To help all OSP users get the most out of the technology, we have prepared the following technical guidelines.
For your watermarking to be effective, especially for advertising and marketing, you must test your embedded images for both watermark detectability and visibility. Focus your testing on common situations, and once you have established that your watermarks can be detected in typical environments — run tests using more challenging contexts.
- Use proofs that accurately reflect the final printed images. The best proof is one provided by your commercial printer. The printer's proofing technology maintains the image's color mode (i.e. CMYK) and is calibrated to produce images that closely match the final color and quality of images from the actual printing press.
- The Digimarc Discover app is supported on these smartphones and operating systems. We recommend running tests using the most commonly used mobile devices in your intended market. Different mobile devices can have a significant effect on detectability. In your testing, you are seeking to ensure detectability by representative devices.
- Test in similar lighting situations that your expected audience will be in when interacting with your watermarked content. Low lighting or high glare will reduce the detectability of watermarks. If, for example, you are embedding images for a newspaper, the images must be detectable in a variety of poor lighting conditions: buses, coffee shops, etc. Therefore, newspaper images require a stronger watermark than those which will be scanned in well-lit places, such as a shopping mall or daylight environments. However, as with cameras, don't overcompensate for unusual situations at the cost of increased visibility in more common situations.
To test watermark detectability, try to detect a watermark in several areas of the image. You should be able to detect a watermark within seconds.
Saving and Using Digitally Watermarked Images
The OSP is designed to embed a watermark that is optimal for printing. However, after you watermark an image, you still have several steps to complete in the “downstream workflow.”
The downstream workflow begins at the point you save your watermarked image file. It is important to save the image in a format that preserves the color space (CMYK or grayscale) and does not apply lossy compression algorithms. The downstream workflow continues when you place the digitally watermarked content – images or tint box – in a page layout program and later generate a final, print-ready PDF.
Preserving Color Space
You may have converted RGB original images to CMYK before digital watermarking. Since printing presses reproduce the CMYK color space (except for spot colors, which aren't applicable here), the CMYK color space should be preserved when saving a watermarked image. Commonly used production formats such as EPS and TIFF are excellent for maintaining CMYK and grayscale color spaces.
Avoid Lossy Compression
By definition, lossy image compression techniques such as JPEG discard image data. In the process, lossy compression also unavoidably discards watermark data. Downstream decompression of compressed images attempts to restore image quality, but the integrity of the watermark may not withstand the compression and decompression processes. Such watermarks may no longer be detectable.
Worth noting, lossless compression, such as TIFF, does not discard image or watermark data. You can safely apply LZW compression when saving image files in TIFF format. After files are saved, you can also compress them using StuffIt™ or ZIP compression utilities.
If, due to your workflow or for any other reason, you must save files in JPEG format, use the maximum quality setting. This setting causes the least loss of data and internal Digimarc tests have shown that watermark detectability remains comparable to that of uncompressed images. However, if your workflow involves JPEG compression, you should do all your proofing and testing with images saved as JPEGs. The embedder saves JPEG images at maximum image quality.
A primary consideration in placing images is to avoid scaling. As mentioned earlier, you should try to scale images to their final size before watermarking. Reducing or enlarging an image more than 10% after embedding the watermark can adversely affect watermark detectability.
Cameras without auto-focus, aperture controls, and high quality image sensors have difficulty resolving fine details. Reducing an image more than 5% can push it beyond the capabilities of such cameras to resolve enough detail to detect the watermark.
Enlarging an image can create the opposite problem of reduction. If you excessively enlarge an image, significant portions of the watermark will fall outside the camera's field of view, and the watermark can be cropped beyond detectability.
Another issue with scaling images is that watermarks are designed to be read at approximately 3" to 6", and users will quickly adapt to these boundaries. Reduced or enlarged images may contradict users' expectations about where to hold their devices, even if their cameras are capable of watermark detection at shorter or longer distances.
Generating the Final PDF
In creating the final PDF for production printing, you need to consider color space, compression, and image resampling. Color space and compression were discussed above, and the same principles apply here.
The Adobe PDF Settings dialog has a drop-down option that enables you to set the level of image downsampling when the PDF is generated. Downsampling creates problems similar to lossy compression — if your image was over 450 pixels per inch when it was digitally watermarked (at 100% of its size intended for layout and printing), this setting discards image and watermark data, degrading the watermark and reducing detectability.