JPEGs are for the Web - NOT for Printing

Toronto Fine Art Giclee Printing Articles

Image of cacti

The JPEG image compression scheme and file format was developed in 1986 by the Joint Photographic Experts Group. Hence, J.P.E.G. was born. It was developed primarily to facilitate the reduction of large file sizes through the use of data compression.  At the time hard drive space was tiny, by today’s standards. A large hard drive was just a few gigabytes. It was also slow and extremely expensive. Smaller files are more easily and quickly handled and stored. The JPEG format made it possible for photographers to store more images on their existing hard drives than they would have otherwise been able.

When the internet came along in 1989, file transfer speeds were painfully slow. So, again, it was necessary to use the smallest file sizes in order for them to be easily transferred over the internet at acceptable speeds. Once again the JPEG format answered the call. JPEG files were great for the internet, email, digital cameras and later on, cell phones because internet bandwidth, hard drive space, cell phone storage and cell network speeds were at a premium and large files transmitted far too slowly if at all over the internet. Hence, JPEG files became ubiquitous.

A few years before the JPEG compression scheme was developed, the Tiff  file format (Tagged Image File Format) was developed in September 1986. Files in this format are much larger than JPEGs because they are not compressed. The Tiff format also supports a bit depth of 16 bit which is far better than 8 bit for high quality image editing and it is required to support the ProPhoto RGB colour space which is the largest of all useable colour spaces. The JPEG format, on the other hand, only supports 8 bit and consequently much smaller colour spaces. But, a data depth of 16 bit makes files twice as large as 8 bit files. While Tiffs can be compressed, losslessly, using LZW or ZIP compression, still, they will never be as small as the JPEG compression scheme could make them. This is due to the fact that image data is discarded by the JPEG compression while it is NOT discarded by the TIFF format. Hence, the JPEG format is “lossy” while the Tiff format is not.

Digital cameras eventually emerged which saved the images they captured in JPEG compressed format. Higher end cameras also allowed photographers to save their captures as Tiff files.

Today, even though internet speeds have improved tremendously since the JPEG compression format was developed, image files from digital cameras have also grown in size dramatically over the years as the capabilities of the camera image sensors have improved and their pixel densities have increased to well over 100 megapixels. So the internet still works fastest with smaller files.

Unfortunately, as mentioned earlier, the JPEG compression scheme works by discarding image data even when the compression setting is set to “Maximum Quality” which is equal to minimum compression. Furthermore, when a JPEG image file is opened in an application such as Photoshop or Lightroom and it is altered in any way i.e. edited even slightly and then resaved or exported back into a JPEG file, that file is recompressed using lossy compression again which causes more image data to be discarded. The result is more damage to the file and hence, the image which that file carries.

It is common for JPEG compression to produce artefacts or visible aberrations after editing and resaving multiple times. In short, the damage due to “lossy” compression begins to become more obvious. In fact, if the JPEG is saved at a lower than “Maximum Quality” setting the resulting damage is more severe and it becomes visible sooner. To be clear, simply opening, viewing and closing a JPEG image file does not cause any additional damage whatsoever. But, if the file is altered in any way and then resaved as a JPEG further file damage does result and it is cumulative.

The damage and artefacts created by JPEG compression may not be apparent on a computer screen because computer monitors display images at a much lower resolution than that required for print. Also images are beamed to our eyes via the light of the screen which tends to cover up a multitude of sins.

As mentioned earlier, the JPEG format supports a bit depth of only 8 bit which greatly reduces a photographer’s ability to edit JPEG images without damaging them to the point where the damage becomes obvious. It is immediately apparent, especially in print, in large, smooth, subtle tone transitions in a sky, for example, where tone breaks occur where a smooth tonal transition should be taking place. This can result in tone breaks which can look a bit like a rainbow effect. See the example at the head of this article. This sample has been exaggerated slightly to make the effect more obvious over the internet. But that effect was created as a result of the lossy compression of the JPEG format. The fact is that the file no longer contains enough data, i.e. it has been robbed of the tones required, to support a smooth expanse of sky.

On top of all of this, JPEG files are preprocessed by the camera in terms of sharpening, contrast, brightness and colour based upon the particular aesthetic preferences of the camera manufacturer’s engineers. This cannot be prevented, undone or effectively fixed if the photographer were to prefer an approach which differs from the defaulted JPEG processing. For example, the process of digital sharpening causes increased contrast at image edges. Around those edges one will see black or white contours i.e. outlines. Once these contours are baked into the JPEG file they cannot be cleared away. So, if the owner of the image wants to enlarge it, the contours also grow in size and any JPEG artefacts like the tone breaks mentioned earlier for example are also exaggerated. If tones in the image shadows are lost i.e. plugged or hilight detail is blown out to blank white, these cannot be recovered in JPEG files, while in RAW files they can be. Finally, because the JPEG format does not support 16 bit file depth it cannot support the ProPhoto RGB colour space. Instead a smaller colour space must be used such as sRGB or Adobe RGB 1998 which often results in colour clipping at the printing stage depending upon the colour content of the image, i.e. its colour gamut.

Eventually, in 2003, Thomas Knoll of Adobe came along and invented the Camera RAW developer. Prior to this, the RAW format had not even been accessible to photographers. It was used in camera only to process captured images in the camera processor to generate preprocessed JPEGs or Tiffs. Now that the RAW format was available for processing, the Camera Raw developer, Adobe Lightroom and other RAW processors made it possible to create superior images from the totality of all captured image data. RAW is far superior for image editing as it retains ALL of the image data which is captured by the camera’s sensor without any preprocessing interference by the camera. RAW exposed the difference in quality between a pristine image and one that had undergone data depletion and damaging artefacts due to lossy JPEG compression and preprocessing. The RAW file won the contest of image quality between file formats hands down.

To sum this all up, while JPEGs are great for the internet, email, cell phones and viewing images on a computer screen, when it comes to printing they leave MUCH to be desired and should NOT be used for that purpose. That said JPEG files can of course be printed. But the results in print are sub-standard especially as compared to prints made from 8 or 16 bit Tiff files which had been generated from RAW captures. When the process of editing a RAW image file is finished and the image is exported for print to a Tiff or Photoshop file (which is a form of Tiff file) that file retains all of the data encapsulated by the edited RAW file. Hence, a Tiff or Photoshop file that had been exported from a RAW image file which contains ALL of the image data captured by your camera is a far superior file for print over an 8 bit preprocessed, lossy JPEG made for the same image.

In my view, if an image is worth printing it is worth printing well - as well as possible. If you choose to build a house, would you hire a builder who uses substandard lumber?

Note: The example at the head of this article is an over processed over sharpened JPEG which had been submitted to us for print. The sky area has been darkened very slightly to make the tonal breaks more obvious. But, they were created by the JPEG compression and the fact that the image had been edited and resaved over itself several times.