..by saving digital photos in the most efficient format
You may have noticed how fast your hard drives are filling up with digital photographs if you shoot in RAW and work on your images in Photoshop. This short article is based on an investigation I carried out, to see which format should be used, to provide the most efficient use of disc space WITHOUT any loss of data. For those unfamiliar with these file formats I have a summary at the bottom.
Below is a picture that shows the file sizes for various formats of the same image file, captured RAW as a Canon CR2, then converted to DNG or opened in Photoshop and exported as a PSD or TIFF file, then these were converted to DNG. I then did a similar exercise with multiple layered images to compare PSD and TIFF. Note that opening a RAW file in Photoshop, and saving it again in PSD format WITHOUT any modifications at all, increases file size from 28.5 MB to 123 MB! So the way that you work with images and the file types chosen has a huge effect on the disk space taken by your images.
1. Always shoot RAW only – I don’t bother capturing JPEGs at the same time, it wastes space, slows down your camera and can cause confusion on the computer as they have the same file name. If I want a JPEG I just export one from Lightroom in the size I need for the specific application. Your will have to resize anyway for web use and doing this from a JPEG reduces quality. So a full size JPEG of a 22MP file is really pretty useless!
2. Converting RAW to DNG is worthwhile – a 14% saving with no loss if you are a Lightroom user, though some limitations in Aperture. ( I should point out that the camera makers own software like Canon DPP does not support DNG).
3. Using Lightroom rather than Photoshop for editing tasks where possible will save a staggering 80%+ of space as Lightroom stores the changes as a small file of metadata rather than as pixels. This approach points the way forward for digital imaging software.
4. Save Photoshop edited files in PSD format especially multiple layer files.
5. Converting the TIFFs that you have to DNG saves a huge 38% of space (Lightroom users only, Aperture doesn’t support or enable you to do this, and neither does Adobe DNG Converter).
6. Converting the TIFFs to PSD format saves 19% of space – less effective than DNG conversion but the best choice if you are an Aperture user – OR HAVE LAYERED TIFFs.
Here is a step by step guide for how to do this. Click on the pictures to get a clear enlargement.
Note: If you have been working on files in Photoshop, creating layers and then saving as TIFF’s.
To convert your TIFFs to DNG you must first take a look at them to ensure that they are single layer TIFFs – converting to DNG flattens the layers and you may want to keep the separate layer information to access in Photoshop. It is easy to determine which TIFFs are flat and which are layered by looking at their size in Windows Explorer or the Finder. On the Mac I open a finder window and search my hard drive for .tif and then view by size. It will be obvious which ones are layered as they will be considerably bigger than the norm. The single layer TIFFs for a 21MP camera image are 168-169MB whereas the multilayer TIFFs are far larger – double or more. The larger ones you need to convert to PSD format prior to converting the rest in Lightroom to DNG.This is a case of opening them in Photoshop and saving them as PSD format.This is unfortunately rather time consuming, it may be easier to copy these files to a different location, working on them as a batch in Photoshop. Only once you have done this can you use Lightroom to convert everything else.
Step 0. BACKUP YOUR MACHINE – just in case!
Step 1. Choose all the photos you want to convert, either by catalogue or by folder, here I have chosen ALL PHOTOS.
Step 2. Enter Library Mode and choose grid view if not there already
Step 3. Choose METADATA at the top of the screen, hold down the title on one of the four columns below eg.LENS and choose FILE TYPE.
Step 4. Choose the RAW and TIFF files Hold down CMD or shift to multiselect
Step 5. Select all of the pictures, EDIT > SELECT ALL
Step 6. LIBRARY Menu > Convert to DNG> See dialogue for options.
Step 7. Go and find something else to do for a while, this part may take some time.
Please note the warning NEVER tick [Lossy Compression]– This converts you RAW files into JPEGs within a DNG wrapper. And there is no warning that your valuable RAW files would be permanently damaged by data loss if this is ticked!
Background and file formats.
The advantages of shooting in RAW are considerable in terms of image quality and increased ability to modify the file on your computer. In the early days of digital photography, memory cards were expensive and buying a large enough card to save lots of RAW images was a prohibitive expense, also computers would struggle to manage the larger file sizes, and there wasn’t any really good RAW workflow software available, but that is no longer the case. Memory cards are cheap (cheaper than film!), computers are much faster and Aperture and Lightroom have transformed the way we work with digital images.
There are several choices to be made when working and saving images with regard to file format.
jpeg. This popular format uses lossy compression and is not recommended for shooting or archiving, jpeg is a format to OUTPUT your images in for upload to the web or to send to friends etc. It should not be regarded as a CAPTURE format as a large part of the original captured image data is thrown away reducing the available dynamic range, and the camera adds noise reduction and sharpening that cant be reversed.
RAW format. This is the recommended capture format if your camera has this facility – if it doesn’t I suggest you get a camera that does! It is such an improvement over jpeg! There are unfortunately many different RAW formats because the camera manufacturers have decided to create bespoke formats for each CAMERA – not for each make but for each actual camera! Confusingly these are usually named according to make eg. Canon are called .cr2, Nikon .nef etc.
DNG or Digital Negative is Adobe’s non proprietary version of RAW. The camera manufacturers RAW formats can be converted losslessly to DNG with a useful reduction in size and hopefully a guarantee of future compatibility. Some forward thinking camera manufacturers now record in DNG format rather than their own, though sadly this does not extend to the two biggest Nikon and Canon. While DNG is primarily designed to provide an alternative for RAW camera files, it is also possible to convert TIFF and JPEG into a DNG – though obviously this does contain only the data present in the source file – it is not a full RAW file, but a “Linear DNG”. The benefits of converting JPEG to DNG are limited and the file size INCREASES, but converting TIFF to a linear DNG reduces file size. It was this discovery that lead me to write this article. I should point out at this point that Apple’s Aperture DOES NOT SUPPORT LINEAR DNG, it only supports camera manufacturers DNG and then to a limited extent. Read about that here
TIFF is a universal format that can be either lossy or lossless depending on the choices made when saving the file. The advantage of it is that all imaging applications can open any TIFF file and it is often used when exporting/importing to other appliactions. eg. HDR software typically outputs TIFF files. The problem though is that despite using compression it is less efficient than either Adobe’s PSD photoshop format, especially when saving multiple layers and also single layer images are larger than Linear DNG.
PSD is Adobe’s Photoshop format. It is at it’s best saving “work in progress” multiple layer files from Photoshop.