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Images for print generally require editing or improvement to achieve suitable results on the printed page. Issues concerning colour saturation, accurate conversion between colour modes or single tone (grayscale) quality are recurring issues.
Supplying a colour image for grayscale output on a black & white or single colour print project, without the correct mode conversion and correction is a particular area regarding quality concerns. For a desirable printed result, images must be converted to grayscale and the steps illustrated below followed to produce an appropriate file. (See Colour Modes & Management for further information)
The following step-by-step guides provide specific information regarding common problems affecting image quality. (based on CS2 version)
- Resize the image to the required output resolution and size.(See Image Resolution for further information)
- Select ‘Filter’, then ‘Sharpen’, then ‘Unsharp Mask’. The options here control the amount of contrast Photoshop applies along the edge of areas containing different pixel content. The default values for radius and threshold will be suitable for most images, however experimentation may produce suitable results. The degree of sharpening is determined by the amount percentage. Typically a value in the range of 50-100 will suffice, but for larger images a higher value will be required. Oversharpening can produce a noticeable halo effect, however the effect of this filter are less pronounced when printed.
- If required, select ‘Image’, then ‘Adjustments’, then ‘Curves’. Manually adjusting the curve will change the overall tonality and adding points to the curve (by clicking) will allow the adjustment of particular image areas from point to point. You can adjust all or target individual channels.
- If required, select ‘Image’, then ‘Adjustments’, then ‘Levels’. The sliders here allow you to compress the shadow and highlight values to match the image content for better output results. You can adjust all or target individual channels. Moving the end sliders below the histogram alters the darkest and lightest pixels within the image and remaps the black or white point to your new value. Adjusting the middle slider affects the gamma (brightness) to make the overall image darker or lighter.
- If required, select ‘Image’, then ‘Adjustments’, then ‘Brightness/Contrast’. This is a basic adjustment that affects every pixel in the image. Used sparingly it can apply greater overall contrast than either ‘Curves’ or ‘Levels’, especially on grayscale images.
- If required, select ‘Image’, then ‘Adjustments’, then ‘Hue/Saturation’. Under ‘Edit’ you have the option of altering the entire colour space, or individual colour components. Adjusting the values for hue, saturation and lightness can shift the colour through the spectrum and change the colour depth.
- If required, select ‘Image’, then ‘Adjustments’, then ‘Color Balance’. Adjusting the values for shadows, midtones or highlights can change a specific tonal range and improve the mixture of colour within focussed areas.
- If required, select ‘Image’, then ‘Adjustments’, then ‘Shadow/Highlight’. This command is a new feature for CS versions of Photoshop and corrects the lighting of an image. You can individually control the shadows and highlights to brighten detail lost in shadow or correct overexposed elements.
Resize the image to the required output resolution and size.(See Image Resolution for further information)
- If required, Select ‘Image’, then ‘Mode’, then ‘Grayscale’.
- Select ‘Filter’, then ‘Sharpen’, then ‘Unsharp Mask’. The options here control the amount of contrast Photoshop applies along the edge of areas containing different pixel content. The default values for radius and threshold will be suitable for most images, however experimentation may produce suitable results. The degree of sharpening is determined by the amount percentage. Typically a value in the range of 50-100 will suffice, but for larger images a higher value will be required. Oversharpening can produce a noticeable halo effect, however the effect of this filter are less pronounced when printed.
- If required, select ‘Image’, then ‘Adjustments’, then ‘Curves’. Manually adjusting the curve will change the overall tonality and adding points to the curve (by clicking) will allow the adjustment of particular image areas from point to point.
- If required, select ‘Image’, then ‘Adjustments’, then ‘Levels’. The sliders here allow you to compress the shadow and highlight values to match the image content for better output results. Moving the end sliders below the histogram alters the darkest and lightest pixels within the image and remaps the black or white point to your new value. Adjusting the middle slider affects the gamma (brightness) to make the overall image darker or lighter.
- If required, select ‘Image’, then ‘Adjustments’, then ‘Brightness/Contrast’. This is a basic adjustment that affects every pixel in the image. Used sparingly it can apply greater overall contrast than either ‘Curves’ or ‘Levels’, especially on greyscale images.
- If required, select ‘Image’, then ‘Adjustments’, then ‘Shadow/Highlight’. This command is a new feature for CS versions of Photoshop and corrects the lighting of an image. You can individually control the shadows and highlights to brighten detail lost in shadow or correct overexposed elements.
As a general rule grayscale images usually print well when adjusted to appear slightly too light on the monitor. Darker images can loose a large amount of midtone detail (especially on newsprint or specialty uncoated stocks) and appear filled-in when printed.
- Select ‘Image’, then ‘Mode’, then ‘CMYK Color’.
- In the History palette (if not visible turn on via ‘Window’, then ‘History’) check for any colour shift by moving between the available states, showing the file in both colour modes.
- If required, select ‘Image’, then ‘Adjustments’, then ‘Hue/Saturation’. Under ‘Edit’ you have the option of altering the entire colour space, or individual colour components. Adjusting the values for hue, saturation and lightness can correct any shift or loss of colour.
- If required, select ‘Image’, then ‘Adjustments’, then ‘Color Balance’. Adjusting the values for shadows, midtones or highlights can correct any colour shift across the entire image and improve the balance within a specific tonal range.
