Beginner Tutorial 11
The vast array of memory cards available for your camera – categorised by manufacturers and the SD Card Association according to memory capacity and write speed – can be bewildering. This tutorial offers a handy guide to what it all means, so you can buy with confidence.
How are pictures stored?
Learning to take pictures is one thing, but it’s also important to give a little thought to the one piece of equipment that without it renders the camera useless – the memory card.
Digital cameras generally save captured images to a removable ‘flash memory’ card.
Flash memory means the data is written/rewritten to a ‘solid state’ (no moving parts) silicon chip and stored indefinitely, without needing power.
Saved images can be reviewed, edited or deleted either on the camera or by uploading to a computer. In the next tutorial we will be looking at how to deal with the images on a PC, and other devices, but for now we are going to concentrate on storing the images on to the card.
The most common type of recording media used in digital cameras is the postage stamp-sized SD (Secure Digital), although the larger format Compact Flash cards are still used in some top-end DSLRs.
How do memory cards vary?
Launched in 2000 jointly by Panasonic, Toshiba and SanDisk, the SD memory card is the No.1 media format for digital cameras, with more than 1,000 members of the SD Card Association offering thousands of compatible products. Its main advantages are size, robust design and data transfer speed – which, along with capacity, has improved continually.
Today, there are many different types of SD cards, all with differences that affect a camera’s performance, and should guide your buying decision:
SD cards are categorised by storage capacity (although actual useable space is somewhat lower due to OS files):
The original SD card (Standard capacity) can now hold up to 2 gigabytes of data, up from 8 megabytes at launch and available in various values in between. The breakthrough 1GB card became available in 2003.
High capacity (SDHC) card sizes start at 4GB and go up to 32GB. SDHC devices will accept older SD cards, but older SD-compatible devices may not accept SDHC.
Extended capacity (SDXC) card sizes start at 48GB and have the capability to go up to 2 terabytes. When 64GB cards launched in 2009, SD card memory was taken to a whole new level! These cards must only be used in SDXC compatible devices; if formatted in older devices, the file system is erased, rendering the card incompatible with SDXC devices.
High capacity with High-speed Interface – with the commonality of SDHC and SDXC cards being used to store large-sized files, there was a requirement for faster data transfer speeds, hence the introduction of the Ultra High Speed BUS interface versions (see UHS – Speed Class below).
When SD cards became popular for camcorder usage, it became necessary to indicate their minimum write speed, as shooting video requires a reliable minimum data rate. Maximum write and read speeds are sometimes quoted by card manufacturers, although it is not mandatory it does give a guide to how quickly stills and video can be copied or transferred to your computer. The SD Card Association classifications are:
Speed class 2 supports a minimum write speed of 2 MB (megabytes) per sec, suitable for Standard Definition video. Theoretical maximum data rate up to 12.5MB/sec.
Class 4 supports a min. speed of 4MB/sec, suitable for HD (720p/1080i) video and digital stills camera, up to 10MP, ‘burst’ shooting. Theoretical max. up to 25MB/sec.
Class 6 supports a min. speed of 6MB/sec, suitable for Full HD (1080/24p and 25p) video and digital stills camera, over 10MP, burst shooting. Theoretical max. up to 25MB/sec.
Class 10 supports a min. speed of 10MB/sec, suitable for Full HD (1080/50p) and 3D video and DSLR burst shooting. Theoretical max. up to 25MB/sec.
Ultra High Speed – Speed Class
In 2011 hardware manufacturers started to include an Ultra High Speed BUS Interface (UHS-I) on board their SD products. So a new compatible speed class was introduced for SDHC and SDXC cards, with a new theoretical maximum write speed up to 104MB/sec. UHS-I Speed Class 1 also supports a minimum continuous write speed of 10MB/sec, making it suitable for real-time broadcast and the higher DSLR Full HD video bit rates.
The ultra-high transfer speed paired with the higher capacity SDHC and SDXC cards, makes UHS-I ideal for capturing and transferring large- HD files and digital stills RAW shooting.
Ultra High Speed for a new generation of video users – with the introduction of 4K video recording and the requirement for ever faster data speeds, two additional SD speed classes were launched in 2014 – UHS-I Speed Class 3 and UHS-II Speed Class 3.
UHS-I Speed Class 3 supports a minimum continuous write speed of 30 MB/sec. with a theoretical maximum data rate up to 104MB/sec. making it the first consumer based media card to support 4K2K video.
UHS-II Speed Class 3 supports a minimum continuous write speed of 30 MB/sec. with a new theoretical maximum data rate up to 312MB/sec. for ultra-fast transfer!
(Note: UHS performance requires compatible UHS Speed class devices; use in non-UHS devices will reduce max. data rate to 25MB/sec.)
What the numbers on an SD memory card mean:
- Memory Capacity – Storage size of the card
- Speed Class – When it is used with a conventional device
- UHS Speed Class – When it is used with a UHS-I compliant device
- UHS -I – This indicates that the card is supported by the UHS-I interface
- Maximum read and write speed of the card
When considering the data speed of SD cards and their suitability for video for example, remember that video bit rates are usually quoted in Mb/s (megabits per second) whereas SD cards quote MB/s (megabytes per second); 8Mb = 1MB.
What are the file types and how many can I store?
Most digital cameras offer the JPEG format for stills storage – a highly compatible and efficient compression format. Compact System Cameras and DSLRs also offer RAW – capturing/retaining uncompressed image sensor data, resulting in much larger files and requiring dedicated computer software for viewing and ‘developing’.
Video files can be offered in various compression formats, including MP4, MOV, AVCHD, Motion JPEG and MPEG4 (H.264). Which you choose depends largely on how you plan to view or edit content later. Using the video recording function is covered in our Intermediate module.
The number of images/videos you can fit on a card obviously depends on file size and the card’s capacity. The size of each file varies, however, depending on three factors:
- Resolution – for stills and video, the number of pixels contained is a factor, with the higher the ‘res’, the larger the file.
- Compression level – different amounts of compression can be applied. For video, it depends on the recording format, a good indication being the bit-rate. The higher this is, the larger the file. With JPEG stills, the menu offers two compression levels – Normal: high compression = normal picture detail, smaller file size and Fine: low compression = high detail, but larger files.
- Scene content – compression systems work by calculating how much detail must be reproduced for each image. In a low-detail scene, like a person standing before a plain wall, a lot of unnecessary detail can be discarded without unduly affecting picture quality. In a highly detailed scene, like a waterfall surrounded by greenery, much of the content is retained, resulting in a larger file.
Considering the above, here are some ‘rough guide’ capacity examples:
|JPEG (12MP Fine)||1GB card = 160||4GB card = 650||32GB card = 5,200|
|JPEG (12MP Normal)||1GB card = 320||4GB card = 1,280||32GB card = 10,240|
|RAW + JPEG (16MP Fine)||1GB card = 34||4GB card = 136||32GB card = 1,090|
|RAW only (16MP)||1GB card = 50||4GB card = 200||32GB card = 1,600|
|AVCHD video (FHD 17Mbps)||1GB card = 6mins||4GB card = 28mins||32GB card = 240mins|
|Motion JPEG (HD 720)||1GB card = 4mins||4GB card = 16mins||32GB card = 130mins|
Still picture and video record quality can be set in the menu before shooting (see LUMIX example below):
So, don’t be shy when it comes to using the full capacity of the card. SD cards are relatively inexpensive, considering their re-usability. All images can be reviewed/deleted while you shoot, and the camera display indicates how many more shots will fit on the card.
One word of caution: SD card quality varies between manufacturers – don’t risk losing precious moments due to card failure! Choose reliable, trusted brands and take care when inserting and removing cards.
The LUMIX Advantage
As a founder member of the SD Card Association, Panasonic has the experience and manufacturing expertise to offer exceptionally high-quality SD cards.
Backed by the ‘PROOF 7’ quality standard, a sophisticated ‘Smart Guard’ data-protect function, ensuring fewer data defects, and an MLC (Multi Level Cell) flash memory, these cards provide a rewriting cycle 10 times greater than conventional Triple Level Cell memory.
SD, SDHC and SDXC are trademarks or registered trademarks of SD-3C, LLC.
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