9 December 2015

Jpeg, RAW, sRGB, AdobeRGB, which should I use?

It may be worth remembering some of the often ignored factors that influence the quality of a digital image.  Different camera manufacturers use different Jpg encoding/decoding algorithms which can affect the quality of the produced Jpg file.  The in-camera Jpg compression settings can also have a great affect on image quality.  A Jpg file is only an 8 bit image and if one is only going to post the file on the web, or view it on a PC or TV screen the recommended colour space is sRGB, which cannot accommodate the full colour gamut of the original scene.  (Poor rendering is not limited to Jpg engines.  There are some pretty serious issues regarding Adobe Lightroom’s ability to properly render RAW files from both Fuji cameras and Canon Eos 5DS/DSr cameras and the Nikon D810.)  https://photographylife.com/adobes-poor-handling-of-raw-files#more-119890

If, however, your intention is to produce an exhibition quality print, the colour space of choice would usually be AdobeRGB.  This colour space can accommodate a wider gamut of colours than the sRGB profile, as can a modern inkjet print, therefore it would be beneficial to set the camera to the AdobeRGB colour space if the JPG files produced by the camera are going to be used to produce the print.  

Shooting RAW with a 16 or greater bit depth would be an advantage, as the full 16 bit colour depth would be present in the RAW image.  Once processed, this colour depth can be preserved by converting the result to a Tiff file with the AdobeRGB or ProFoto RGB colour space profile.  This file should be used to generate the final print, as converting it to a Jpg file will sacrifice some of the colour gamut even if the Jpg is low compression and AdobeRGB colour space.  

There is no advantage in setting the camera to sRGB colour space for Jpg output and then converting the files to AdobeRGB afterwards for printing.  The original sRGB files will not contain the full colour gamut possible with AdobeRGB anyway.  Regardless, colour management is a whole other subject.  This may be of interest:  https://helpx.adobe.com/lightroom/help/color-management.html

Opening a Jpg file in Adobe Camera Raw for editing does not convert the file into a RAW image.  This is not possible.  It simply allows one to use the editing controls of ACR on the Jpg file.  ACR does not have a particularly good Jpg engine and Jpg files edited in ACR can have unpleasant artefacts, depending on which make and model of camera produced them.  Far better results can be had by opening the original camera Jpg file directly in Lightroom or Photoshop or PSP for editing.  If using Photoshop, make sure that the working colour space matches that of the image file.  i.e: If the camera is set to sRGB, set the working space to sRGB and if the camera is set to AdobeRGB, set the working space to Adobe RGB.  Setting the camera to sRGB and the editing software colour space to AdobeRGB and then converting the file to AdobeRGB for editing is a negative exercise.

If you use Adobe Lightroom to edit your RAW files, Lightroom will automatically display the image in the library module as sRGB.  If you open the image in the “develop”module, it will be displayed as Pro-FotoRGB, which is an even wider colour gamut than AdobeRGB.  If you then export the image from LR, you are offered the opportunity to set the colour space of the exported file to any profile you choose.

Having said all that, most people will never tell the difference between an image produced ex-camera as a Jpg low compression sRGB or as AdobeRGB colour space, or between a Jpg Fine and a Jpg Normal (especially with a Nikon set to “Optimal Quality” in the setup menu.)  To make very good prints up to 16X20 you don’t need more than 10mpx and some say even less, depending on the print resolution chosen.  300ppi is only necessary for prints viewed at arms length.  Exhibition prints are commonly viewed at much greater distances and therefore the resolution in ppi can be much lower without affecting the apparent quality of the image.  An advertising billboard is printed at 10ppi.  If pixel peeping floats your boat, by all means print your murals at 300 ppi, but you will waste a lot of computer storage space and you will need a powerful PC!   The main advantage in having a high resolution camera is the ability to crop the image without having to re-size the result to compensate for the “lost” data.

Most of the latest generation digital cameras, even the inexpensive point-and-shoot models, will produce images straight from the camera of sufficient quality to be usable without further processing.  Press the shutter release, take the memory card to a good high street photo lab, have a poster sized print made, hang it on the wall and go “Wow!” every time you walk past.  It can be that simple.

Finally, the old adage:   While the equipment helps, it’s the brain behind the camera that creates the photograph.     

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