There's no doubt that the digital still camera (DSC) revolutionized the photography industry. The ability to easily review, edit, and share photos has proven to be a significant advantage for consumers.
And as consumers and professionals became savvier with digital photo editing and publishing, the need for higher resolution pictures also grew. DSCs started to increase the resolution of the pictures they were capable of capturing in order to meet this demand, with resolutions of 10 Megapixels not uncommon today.
For maximum photo quality and photo manipulation flexibility, some DSCs also feature raw uncompressed "digital negative" formats. The result of increasing photo quality and resolution has also led to increasing file sizes, which can reach upwards of 20MB in size.
To accommodate these increasing files sizes, larger memory storage is required, enabling consumers to maintain or increase the number of photographs they may take for a given storage medium.
While increasing storage capacities have solved the photo storage challenge, they bring with them new challenges for designers. Specifically, DSCs have not been optimized to handle the processing and transfer of such large amounts of data.
The first challenge lies in transferring large amounts of data to a PC for editing, printing, or publishing. While USB has become the de facto standard for connecting a DSC to a PC, the USB performance in DSCs may not have been optimized for handling large amounts of data. To illustrate, the graph in Figure 1 below shows USB transfer times for a few of the DSCs available on the market today.
|Figure 1. USB transfer time for 980MB of photos.|
As shown in the graph, transfer times can take from 2.5 min upwards to16min for 950MB, translating to transfer rates of 6MB/s to under 1 MB/s. With more users transferring larger amounts of data, consumers will not tolerate longer wait times for data transfers.
Longer transfer times also have the side effect of increasing battery drain on the DSC. DSCs today do not charge while connected to a PC, therefore the longer a DSC stays connected to a PC, the more battery drain that occurs. For a consumer, one of the most frustrating experiences while using a DSC is to have the battery drain completely during a file transfer.
With consumer demand for transfer times in seconds, not minutes, transfer rates of less than 10MB/s are no longer acceptable. To understand the reasons for these slower transfer rates over USB, it is useful to take a closer look at the data transfer path when copying files from the DSC to the PC (Figure 2 below)..
|Figure 2. File transfer in a typical DSC|
Most DSCs today feature removable storage in popular formats such as SD or Compact Flash. The removable storage is typically connected directly to the processor via the corresponding storage controller.
To copy files from the DSC to a PC, the data is first accessed from the removable storage by the processor. Next, it is buffered into SDRAM before being sent to the PC via USB. As shown in Figure 2 above, this data path is not direct and thus impacts the USB performance.