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Improving image quality
Calibrate your monitor
The appearance of your digital images will vary according to the monitor you use, and again on the printed page. One vital operation to carry out regularly is to calibrate your monitor. This can be done with specific software packages and on screen meters, or more easily with the Adobe gamma software, which is an integral part of Photoshop. If using a CRT, make sure that the monitor has been running for around half an hour before the calibration process, and that any ambient light is consistent with the normal working environment. Another important point is to make sure that you have a neutral grey desktop on your monitor, against which to view the images.
Colour Space
Unless you have reason to do otherwise, we recommend you use Adobe RGB (1998). This has become the defacto standard for most imaging professionals.
Colour Management
This is a matter for your own workflow. Alamy will disregard any embedded ICC profiles.
Exposure
The histogram is a graphical representation of the tonal values in an image. Check, and if necessary correct, exposure using the histogram (Levels). For most images the black point should be at or near 0, with the white point at or near 255. At Alamy we expect the black/white points to be within 5% of these values, i.e. black at Level 12 or below, and white at Level 243 or above. There are exceptions of course - for example, extreme high-key or low-key shots, and misty, atmospheric images may not contain the entire tonal range from black to white. This is perfectly OK.
In Levels, if most of the tonal values in the histogram are bunched up towards the left, the image is probably under-exposed. If bunched up towards the right, it's probably over-exposed. Use the centre slider (gamma) - or for more control use Curves - to try to improve matters, but there's a limit to how far you can go before image quality deteriorates. Raw shooters should go back to the original Raw file and make corrections there.
Noise Reduction
There are various software packages available for noise reduction. While some of these packages achieve very good results, they generally work by softening the image. We advise that you use them sparingly to avoid introducing softness and unsightly artifacts in your images, and to check your results at 100%.
Interpolation
When an image file is increased in size, software has to 'create' extra pixels to fill the gaps. It does this by estimating the brightness and colour of the new pixels, based on their neighbouring pixels. There are specialist software packages and techniques available, some methods are more successful than others. We require scans to be un-interpolated and digital camera files to be interpolated up to 48 – 50MB. If you have a camera that is capable of producing an uncompressed 8 bit, TIFF file size of over 48MB then leave it that size. If you need to interpolate your image’s digital camera files you must ensure that you use a professional software package, such as Abobe Photoshop.
Check for a colour cast
With the Eyedropper Tool set to a sample size of 5x5 pixels, place the cursor over a known neutral (black, grey or white) area. Now check the RGB values in the Info Palette - they should all be identical. If they're not, use one of the various colour balance methods to make them equal.
Sharpening
The normal process of preparing an image for repro always includes sharpening. This is best done only once. If you apply sharpening to sharpening, unsightly artifacts can appear. So, please do not sharpen at any stage of your workflow.
Grayscale Images
If you are working with grayscale images, please save them as RGB prior to submission.
Check your images at 100%
Always carefully check the quality of your digital files at 100% before you submit them to us. 100% means that one monitor screen pixel is displaying one image pixel. This is the only way to see every pixel in your image, it is important that you check all of your images at this zoom. In Photoshop, the keyboard shortcut for 100% is Ctrl+Alt+0 (PC) or Cmd+Option+0 (Mac), or double-click the zoom tool.
Save your file
Save the image as a high quality JPEG file (level 10 or above in Photoshop). Ensuring your file name includes the ‘.jpg’ extension. You can set up Photoshop to automatically add the extension by going Photoshop > Preferences > File Handling > File Saving Options and select Append File Extension "Always".
Further help
- Achieving the best results:
- Recommended camera list
- Images from digital cameras
- Images from scanners
- Improving image quality
- Retouching techniques
- The Alamy Forum - the answer may be there.
- Resources - photographer tips and a directory of scanning and keywording providers.