Digital Image Quality

Given reasonable camera technique, modern digital cameras are capable of capturing all the colours our eyes can see, and distinguishing shapes and tones with very great detail.  In other word, they can make great photographs.

Poor quality digital images are often the result of wrong decisions in handling digital data, rather than anything wrong with photographic technique.

If you want to share your photographs, either on screen (projected or on the ‘web’), or in print, you need to be able to make the most of the image data your camera captured.

Image Quality

High quality images, which:

  • are sharp where they need to be, and
  • retain the maximum number of original pixels, and therefore the maximum amount of colour and tone information from the original capture;

can be very satisfactorily enlarged for exhibition sized prints which retain maximum detail and colour, and they can be equally satisfactorily downsized, retaining optimum colour and detail for digital display.

On the other hand, images that have been compressed, or downsized, or have had colour information thrown away, often cannot be satisfactorily upsized for printing. Enlarging such images usually introduces jagged edges, ‘pixelated’ areas, and stray colour ‘artefacts’. In short, they’re no good.

Adjusting, correcting, enhancing and otherwise editing image files

A fantastically composed, and wonderfully sharp image that tells an amazing story, can often be made even better by judicious cropping, adjustment of white balance or contrast and so on. Most digital photographers use some software program or other to make such ‘improvements’.

Two rules:

Rule 1: Don’t edit original image files

If you make an error in editing an image and it becomes unusable you can always retrace your editing steps on another copy of the original file. You can never recreate the original file if you have edited the original pixels, especially if you also broke Rule 2!
Only ever edit a copy of your original.

Rule 2: Don’t edit JPEG files (unless you have no choice)

The enemy of straightforward quality printing is JPEG, because, by its nature, JPEG approximates colour and tone values in individual pixels, in order to achieve a smaller — compressed — image file size.

When an image is saved in JPEG, information is thrown away. Irretrievably. (Why?) To make matters worse, every time a JPEG file is opened, edited and re-saved, further compression and further loss of information takes place. If you broke Rule 1 your original is lost forever.

JPEG suffers from two other disadvantages:

  • it saves files in an 8-bit file format which introduces the risk that edits in areas containing subtle tonal gradients will become jagged or ‘posterised’ because changes are either ignored or overdone;
  • by default (although you may over-ride this), saving an image in JPEG format converts all colour information to fit in the sRGB colour space, which risks watering down some of the more saturated colours in your image. All of this means that, to make the highest possible quality image for printing, you should not edit JPEG files unless you have no choice.

Options for capturing and storing images to make high quality photographs

A very good option is to ‘shoot’ in RAW, and use your computer’s software to handle RAW conversion, and colour and tonal corrections.

However, the options you have depend on whether your camera is capable of saving RAW files or not, and what kind of photo editing software you have.

1: My camera only saves JPEGs

Save original JPEG, edit a copy and save TIFF (or PSD)

All digital cameras actually ‘shoot’ in RAW. However, not all cameras give you the option of saving the RAW file; instead, a dedicated computer inside the camera converts the image to JPEG before saving it to your memory card.

If your camera saves only JPEGs then:

  • set it to record ‘LARGE‘ (and/or ‘FINEST’) — the biggest, highest resolution JPEGs your camera can make. (Some people assume that small files are better because more will fit on a memory card. That is true, but the price you pay is degrading the quality of your pictures.)
  • set it to record images in the AdobeRGB colour space (rather than sRGB), (why?) and …
  • after you have downloaded the original image files and saved them on your computer, open the pictures that you may later want to print, and ‘Save As’ in TIFF file format.

A TIFF file can be further edited and printed, but it is not compressed. Image data is not deliberately thrown away in processing TIFFs.

You can open and edit the TIFF file if you want to do any further editing. That way, the original JPEG will remain without further compression as a sort of Master back-up file in your pictures directory, and any edits you do on the TIFF copy of the file will not cause unnecessary image degradation.

If you are editing in Photoshop you can safely open the copy of your original JPEG because Photoshop will convert it internally to a proprietary format for editing, anyway.  When you have finished editing ‘Save As’ PSD, or TIFF (preserving layers if you may come back to do further editing.)

2: My camera allows me to save RAW, but I don’t have a dedicated RAW processor.

Shoot RAW, process TIFF, save as TIFF

Shoot in RAW, and use the software that came with your camera to handle RAW conversion and initial colour and tonal adjustments then export (or ‘Save As’) the image as a TIFF file.

When you save as TIFF you will likely get the option to ‘embed AdobeRGB colour profile‘ — choose this option to preserve as much colour information as possible. Do not choose sRGB if you have a choice.

Now open and edit the TIFF file if you want to do any further editing. That way, the original JPEG will remain without further compression as a sort of Master back-up file in your pictures directory, and any edits you do on the TIFF copy of the file will not cause unnecessary image degradation.

3: My camera allows me to save RAW, and I have Photoshop, or Lightroom, or …

Shoot RAW, process RAW, and export to any other required format, such as TIFF or JPEG only after you have finished raw processing.

Good RAW converters, such as Lightroom, Luminar, Digital Photo Professional, Affinity and Adobe Camera Raw (ACR), (which is part of Photoshop and Photoshop Elements) enable almost all the RAW photo adjustments, including cropping, straightening, colour and tonal adjustments, spot and red-eye removal, sharpening and noise reduction, that you could want.

LightroomLuminarDigital Photo Professional, AffinityPhotoshop and Photoshop Elements, can also output a print-ready file without requiring you to save in JPEG format.

What about Picasa?

Picasa can convert RAW files and offers some limited tools for adjusting RAW files.

However, it seems to have been built with the idea of publishing on the web only, because it offers no option other than saving compressed JPEGs in sRGB colour space. Those files are not really satisfactory for high quality printing, especially if they have to be ‘blown up’ to a bigger size.


1 thought on “Digital Image Quality

  1. Pingback: News, Updates, Syllabus 2014 and other things | WCC

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