There's going to be a few other things to look at within your comparison in a DVD vs. Blu-ray than just the quality.
Storage capacity is measured in gigabytes, similar to computers and storage drives. A DVD will only be able to store about 4.7 GB of data, which equals about two hours of a movie. A Blu-ray can hold about 25 GB of data, which allows for more high-definition information. It can hold about 13 hours of standard definition information or about two hours of high-definition information. Some of the double-layer discs out there can hold substantially more. This means that, even with a DVD labeled as HD, it's not going to be able to hold the same level of data as a Blu-ray disc simply because of the technology.
The laser technology used to read the two formats varies differently, too. When it comes to the difference between DVD and Blu-ray, A DVD player will use a red laser at 650nm wavelength. A Blu-ray, however, uses a blue laser and reads at a smaller diameter. What this means is that there's a more precise reading of what's on the disc to ensure that there are no skips. It also allows the images to come across more clearly.
In regards to audio, what is the difference between DVD and Blu-ray? DVD formats support a total of three audio formats: Dolby Digital, Linear PCM, and DTS Digital Surround. The Blu-ray hit the scene with the promise of better audio quality. It supported additional formats including Dolby TrueHD, Dolby Digital Plus, and DTS-HD. This has allowed people with home theaters to consistently choose the Blu-ray format more prominently over the DVD because of wanting an exceptional sound to what they were watching in addition to a higher quality of the video.