Transcript
Colour Space We have already discussed the ‘bit depth’ in your images and this relates to the maximum amount of colour gradients that an image is built from. However this is not the only colour management issue to consider. Photographic editing packages will allow you to work in different colour spaces and you need to define one for use across your editing software so it’s consistent. Any image is built from a myriad of colours, and the huge range that you could technically have within an image was defined way back in 1931 by an organisation called the International Commission on Illumination (CIE). This while really just a mathematical exercise did define the theoretical maximum number of colour variations available. The colour space you use will address a significant percentage of this CIE colour space and there are many working colour spaces available. An entire essay could be written on the multitude of other colour spaces available but for most photographers the important thing is to pick a suitable colour space and move on! It ultimately is not going to affect your image quality unless you are printing huge fine art prints where the subtle differences in certain colour spaces can make slight differences to the look of your print. For most photographers the one to choose is sRGB and this is set in your image editing software and camera. Many professional photographers will use this particular colour space and we’d recommend adopting this and not spending too long worrying about it!
What file formats should I save? We have talked at length so far about different file formats, resolutions and outputs and have studied in depth the important RAW file format. Many photographers will wonder what is the best format to save photos in for long term storage? The answer is really that you really need to save at least two files per photo. The first one you should always save is the original RAW file. As the RAW file is a nondestructive file type it means you can make endless adjustments to your RAW file, save it and you can safely open it again and make more adjustments without any fear that you are changing the data in the file. The second file you should save is the highest quality output file that you edited. This could either be a TIFF file or JPEG file. You might ask why bother saving this file when you already have the RAW file saved? The 1
simple answer to this is that you need to save this file, as you may have spent considerable time editing the photo in your editing software post RAW processing. If you don’t save this file but need to use the photo at a later date you will have to re-process your RAW file and re-edit the photo. Once you have these two formats saved (RAW & Your Highest Quality edited output file) you can easily and quickly create lower resolution versions or versions sized for print or web / internet use should they be required.
Printing your image We had in module three overviewed the modern photographic quality inkjet printer so we won’t go over this information again. The only thing to add is that inkjet printers will always give you different quality levels in terms of final print output. You will often hear figures such as 1400 DPI or 2800 DPI output and obviously the higher the DPI output (Dots per inch) the higher quality and ‘smoother’ the print will look. Why would you ever then print at a lower quality level ? The answer is speed. Bear in mind a modern photographic inkjet may take 5 or 6 minutes to produce a print on its highest quality setting whereas on a lower DPI output may print the same print in a minute. If you need to do a huge number of prints time can be a significant factor. Even at lower DPI levels modern inkjets can produce superb quality prints and these may suffice for less demanding applications. Also bear in mind that printing at a lower DPI level is useful if you just want to print a proof print to be sure that all is okay. Printing your image is essentially quite simple. Once you have finished making image adjustments in your editing software you need to resize the image and save a version sized for your particular chosen print output. We have covered a lot of this information already in this module where we had discussed output on a printer, file resolution and the physical size of the image. There are two main things you need to do, first crop the image to the required print size and then sure that the resolution is adequate and correctly set. In relation to cropping the image what you need to do is set the ‘crop tool’ in your editing software to reflect the print size you want to make. You do this simply by entering the print measurements into the ‘crop tool’ for example 1o inches wide x 8 inches tall and then use the crop tool to apply a ‘crop’ of this size to your chosen image. This ensures that ‘what you see is what you get’ in terms of the on-screen image. In other words what 2
you see on screen is what you printer will output in terms of the physical ‘crop’ on the image. As regards resolution you might remember that we mentioned that the norm for printed output is a digital photo with a resolution of 300 PPI (Pixels per inch). This has become a norm but it is not always the ideal resolution to be printing your image at. All printers have what is called a ‘native resolution’ and you need to find out what this is. Epson for example use 360 DPI as the ‘native resolution’ for most of their printers. If you print to your printer with a resolution other than the native resolution the imaging engine in your printer will up sample or down sample the image to match it to your printer’s native resolution. This is not ideal as the algorithms in your printer software are not generally as sophisticated as the algorithms in your image editing software and you can end up with a lower quality print. A problem which often raises its head when your printer has to upsample or downsample your file is ‘Moire’. ‘Moire’ is a French word that refers to an interference pattern. You will see ‘moire’ sometimes in a digital image where you have very close parallel lines within the image. Clothing can often cause moire as the threads or patterns in the clothing are very close together. You can see moire in a photo as a strange interference or distortion in these areas. In essence this distortion is caused by tiny inaccuracies in the digital file when building pixels. It is very off-putting and no photographer wants to see moire in their images. Earlier digital cameras used to have awful problems with moire interference but as sensor technology has improved this is largely a thing of the past in the digital file. HOWEVER if your file resolution does not match the native resolution of your printer and the printer resamples the file to match the printers native resolution inaccuracies can occur and you see print moire. Best therefore to match your file resolution (PPI) to the native resolution on your printer from within your image editing software. Once these two things are done you are ready to print. The actual print window in your photo editing package (you always print your photos from within your photo editing software) will need you to make some more choices. These vary hugely from one print engine to another but the important settings you will normally have to choose relate to the rendering intent, colour management and paper profile. 3
The rendering intent is the piece of software which translates the colour space data stored in your image file to the colour space on your printer. In essence the colour you see on your calibrated monitor is ‘translated’ so the printer can understand it. This is a complicated process which is really beyond the scope of this course but for most photographic prints selecting the ‘Perceptual or Relative Colorimetric’ intent will give you accurate prints. Colour management is a simple one to explain, always, always select the option which lets your photo editing software manage the colour. If you let the printer manage the colour you are introducing another layer of software that interprets colour data and you will typically end up with colours that don’t match what you are looking at on your calibrated monitor. Paper profile is another simple one to explain. All printing media (be it a glossy photographic paper or a more discrete matte finish paper) will display colours in a different fashion. There can be quite significant changes between one brand and another as well. This can mean that one print on a particular paper can display for example a more vivid red than another. Each paper manufacturer then to try and level output, will build a particular paper profile (software) that tells your photo editing software when printing to slightly adjust the colours to reflect the different way that the paper responds to ink. Simply ensure that the paper profile matches the paper you have in the printer. Paper profiles can be downloaded from the paper manufacturer’s website.
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