Pictures Are Files - File Formats


When an image is captured by a camera or a scanning device it has to be saved or memorised in a 'file format'. The information can only be read and understood if the software recognises the format.


The dominant formats are - 
JPEG (Joint Photographic Experts Group).jpg
TIFF (Tagged Image File Format).tif
PSD (Photoshop Document).psd
RAW (Raw Unprocessed Information)


File>Save as - This opens numerous options for the Photoshop/P.C user. For simplicity it is advisable that you save your work as either TIFF or PSD file because they support all of Photoshop's features. Note - Not all formats support layers.


TIFF - This format generally regarded as the industry standard because it is the most universally recognised format. Photoshop's variant of this format supports image layers, adjustments, layers, paths, clipping paths and ICC profiles. It's the most popular format for photographers delivering RGB and CMYK files to clients. It's good practise to flatten recognised files because only Photoshop supports layered tiffs.


PSD - Photoshop's native format supports everything Photoshop can do including ICC profile. Until version 6 it was the only format that supported layers. This format is only by Photoshop so it is not advertisable to hand PCD files over to clients.


JPEG - The most commonly used file format. It has 'lossy' compression that transmits what it deems to be 'important' content and discards colour information hat it considers redundant. There are no options to save without compression but embedding ICC profile is optional.


JPEG allows you to make trade off between image file size and image quality. JPEG compression divides the images in squares 8x8 pixels, which are compressed independently. As you increase compression the squares become more visible.


100% Quality JPEG - Is very hard to distinguish from the uncompressed original typically taking up to 6 times as much storage space. 


80% Quality JPEG - It still looks good although it is 10 times smaller than the uncompressed original. Some deterioration will occur however. 


60% Quality JPEG - 20 times smaller than the uncompressed original. Sufficient for website use.


10% Quality JPEG - This will show image degradation with very visible 8c8 jpeg square. It is unlikely that you will ever use this level of compression but it illustrates what JPEG is doing at higher quality levels.


Photoshop - 3SD (Portable Document Format) - This format can support layer files, they can be re-opened and edited in Photoshop.  A group of images can be saved as a multi page document. PDF supports various compression amongst them are ZIP, JPEG and JPEG 200.


Upon close inspection of compressed JPEG blocks of 8x8 pixels can become evident. Because of this degration it is advisable to avoid saving in this format for high quality images. JPEG can use several layers of compression dramatically reducing the size of closed files compared to their open state. If an image is shot on JPEG avoid re-saving as a JPEG as it will further degrade the image, save as a TIFF.