Now and then, in printed publications, an advert appears that has most probably been supplied as a compressed JPEG (Joint Photographic Experts Group, also known as JPG) when a TIF (also known as TIF, Tagged Image File Format) should have been used – leading to an image that looks blurry and blocky. The advertiser may have been somewhat surprised to see this effect in print as the image would probably have looked acceptable when viewed on screen. Monitors typically have a resolution of between 72 and 100 dots every inch but a colour printer starts at 300 dots every inch (going up very high) so something that looks good on screen may not be so great when printed.
There are a number of others formats, methods and considerations outside of those talked about in this post but in putting this together I have aimed to produce a general rule of thumb to guide non technical users in simply handling images for ultimate use in print.
JPEG uses a “lossy compression” technology (though according to Wiki there are a few loss-less variations out there) to keep file sizes very small. Lossy compression uses a number of techniques to reduce the file size – essentially the result of JPEG compression is to be left with an “approximation” of the image so what you get out at the end isn’t the same as what you put in – it is similar to it.
As mentioned above, computer monitors can be very forgiving of poorly compressed images but print certainly is not; jagged edges, artifacts, blocky images and colour blur are some problems that can be attributed to using a lossy compression method on an image. File sizes however can be very small making them ideal for web sites and for sending via electronic mail.
TIF, on the other hand, typically produces larger files but uses a “loss-less” compression technology so what you get out at the end is the same as what you put in, which can often be a very high quality image. You wouldn’t want to be emailing TIF images around the place – these would probably be burned to a CD or submitted using a secure online file transfer service.
For this example we can take part of a photographic image, originally scanned at 300 dots per inch, and show the effect of saving as a JPEG at its extreme compression levels. This image is 4.86 MB in size when saved as an uncompressed TIF.
All of the images here are screen prints saved as JPEG as this article is entirely web based – though their source is based on the actual format.
The image above is part of the original image saved as a TIF.
Using loss-less LZW TIF compression this image comes out around 2.52 MB and loses no detail during compression – the resultant image is the same as the one we started with.
However, take a look at these images (close up)
Saving the image as a JPEG with maximum quality we get a file size of 1.01 MB and when saved with minimum quality we can get the file size as low as 0.08 MB (83KB but I kept the measurement in MB for consistency).
This file is very small in size and the resultant image is the same dimensions as the original but contains barely enough information to convey the image), notice the block nature where the image has been sliced and diced to approximate the original.
Sometimes an image may originate as a JPEG but then be saved as a TIF which, unless the JPEG is uncompressed or very high resolution, is a pit pointless as the damage is already done. Try to avoid saving JPEG images as TIF as this can often lead to confusion when expectation is for TIF images to be high quality.
Use JPEG for emailing images around (always add a reference to proof in the filename) but ensure the recipient understands this is a screen proof – use TIF for sending the actual production image.
Images destined for the screen are likely to have a colour range of RGB (Red, Green, Blue) but images aimed for print will most likely need to have a colour range of CMYK (Cyan, Magenta, Yellow, Black) so bear this in mind when saving/previewing files. The difference can be subtle but colours may vary between the two. You cannot just change the colour space from RGB to CMYK and expect it to print as expected.
The image on the left shows the RGB colour space but the one on the right shows CMYK – the difference is very subtle but noticeable. Marvin’s Corner has a good outline of RGB and CMYK.
If the artwork is likely to be scaled up or down regularly there is the added advantage of using an EPS format for artwork – this is particularly helpful for vector images, type and logos – but that is another article.
An added complexity is that more and more photography is being carried out using consumer digital cameras, many of which uses JPEG as their preferred format – always try and capture as many dots in the image as possible up front – you can take dots away but you can’t add them back!
Printers may also have specific requirements so make sure you talk to them. If you use a photographer put them in touch with your printer (and vice versa) to ensure they are both on the same page.
There are variations to both of these formats, for example it is possibly to use JPEG compression in a TIF and it’s possible to save an uncompressed JPEG. There are many other formats such as the increasingly popular PNG format (as well GIF) and the use of PDF, PSD, and AI but there is a general rule of thumb that can help when dealing with images that are ultimately destined for output to printed medium:
- Use compressed JPEG’s for proofing work via email and the web
- Use uncompressed (or loss less compression such as ZIP and LZW ) TIF files (minimum 300 dpi) for master files and for printing.