When shooting with an SLR camera and editing in post production, file quality and file sizing is fundamental knowledge.
File quality or the resolution of an image refers to file type or compression used when storing/ the image.
File sizing can refer to the physical size/ dimensions of an image, which is important if you are sending an image for print, and the storage space the image will take up.
Different types of file formats and what they might be used for:
JPG (Joint Photographic Expert Group) – A lossy graphic file/ low level compression. On my Nikon camera you select from three different compression ratios, ‘fine’, ‘normal’ or ‘basic’ and the lower the compression ratio, the better quality the image will be but also the larger the file size.
JPGs have become the most common image file formats and is used from everything from Facebook albums to printing. It is used when you need to have a small file size when you don’t mind compromising some of the image quality. Best uses for JPGs are on websites, social media or sending proof copies to clients in a contact sheet or individual files and highest quality JPGs can be used in print magazines and advertisements.
RAW (NEF) – Raw image files contain all the information captured by the camera’s sensor and records all of the meta data. The image is saved to the memory card as a lossless compressed form (uncompressed). It is one the best format for a photographer to shoot in as you can get the best image quality possible. This will be important when it comes to editing the image, the more data captured the more you’ll have to work with in editing software and the less degradation to the image will occur. You will notice visible differences between editing a JPG and a RAW file. However, RAW files are normally very large so are often converted before sent to print or sent to a client.
TIFF (Tag Image File format) – TIFF is a standard image format in the publishing and printing industry. Similar to RAW, TIFF stores image data in a lossless format, preserving layers, alpha transparency and can be saved and re-saved in photo editing software without loss of quality to the image. A downside to TIFF format is that it takes up an excessive amount of storage space, not all cameras offer the option to shoot in TIFF however you can shoot in RAW instead. TIFF files are best suited for photo libraries like Getty images, so files can be printed on larger scales at higher quality in advertising campaign materials e.g magazine spreads, billboards etc
PNG (Portable Network Graphics – Used typically when a smaller file is needed but without loss in quality as it supports lossless data compression. It is often used for sharing images or graphics on the web as it maintains transparency in layers so it is often used by graphic artists for web design.
Creating A Contact Sheet In Lightroom
Using the software Lightroom I created a contact sheet from a task shoot. A contact sheet is useful to show clients how images will look or to give them the opportunity to pick out their favourite images. Lightroom allows you to add watermarks, change the file names to make the images easily identified and organised and gives you the option to display certain meta data in the caption.
Compression – Compressing an image is the process of reducing a file’s size and you can achieve this in a few different ways. You can reduce picture resolution, apply compression, crop your images, changing file type etc,
Bitmaps are images made up of coloured pixels, which appear as a smooth complete image at a distance, individual pixels may become visible when image is enlarged.
Compressing a lossless RAW file into a lossy small & large JPG file
By reducing PPI (pixels per inch), the quality and changing the colours from ADOBE to sRGB the file goes from 12mb to 170kb. The lo res image will be more pixelated when enlarge and some of the colour data will have been lost, the lo res would be suitable online for social media or a website page. The high res version could be used on an online gallery like flickr or wordpress or for print.