hello sailor

Working with
digital images

 

Digital vs. Analogue

Which is better - film or digital? It’s a huge question, with rational arguments on both sides, and no easy answers. It’s not just about numbers of pixels - lens quality, camera quality and data storage also play a part. So does personal preference. Film supporters can produce reams of calculations demonstrating why film will always be preferable; digital gurus can show you amazing images that are indistinguishable from film images.

As a very rough rule of thumb, you need a digital camera of 6.5 Mpixels or greater to match the resolution of 35mm film.

Some interested third parties still require you to provide slides, but increasingly, you are given the option of providing digital images. In fact, many application and submission procedures are now completely digital. The principal advantage of digital from our point of view is that it is easier to get it into the computer to work with.

So if you prefer to document your work with a camera that uses slide or print film, get into the habit of ordering a CD of the images when you are having the film processed.

 

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More pixels are always better

Resolution matters. The greater the resolution, the more detail you capture in the image. Even if you are going to discard most of the detail later when you are editing the image, it is better to have it than want it.

When you are documenting your work, you don't usually know how the image you are taking is going to be used in the future. It might be used online, where screen resolution is only 72 pixels per inch, so that most of the detail in a high-resolution image will be discarded. On the other hand, it might end up in a printed catalogue, where the print resolution could be 1,200 dots per inch or even higher, which would require a very high resolution image to start with.

For editing too, it is important to have a high resolution image to start with. For example, if you have taken a so-so image of your work, you might find that you could crop it down to a much better photo. You can only do this and retain the quality of the resolution if the original image you started out with is of higher resolution than you need.

If you have captured more detail than you need, it is very easy to resize an image downwards in Photoshop or other Image Manipulation Software.

However, if you have captured less detail than you need, you cannot satisfactorily resize an image upwards. The software will "guess" what the missing details are, but the image will not be as sharp as it should be.

Imagine you have taken a photograph of your work

Then you discover you need to use only a small section of it for an application or submission. Here is a section of a high-resolution photo of the work (lots of pixels)

Here is a section of a lower-resolution photo of the work (not so many pixels). As you can see, there is not as much detail left in the lower-resolution image.

At pixel level, we can see what is going on. High-resolution image   Low-resolution image

So always capture your digital images at the highest resolution available on your camera.

 

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The power of Photoshop

Photoshop is extremely powerful image manipulation and image editing software. Most users only need to know how to use a very small fraction of its functionality. The following areas are of interest to us:

  • We can improve the quality of our images by adjusting settings such as brightness, contrast, colour balance, sharpness, etc., to compensate for problems in the original image.
  • We can use it to re-size images to meet the requirements of assignments, application procedures, etc.

 
There is no doubt that Photoshop can do some pretty amazing things. However, it is no substitute for putting some time, energy and focus into taking a good set of original photographs. That means:

  • using a tripod
  • working in good light conditions
  • taking more than one shot of each set-up, using different settings.

 

 

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Image size

If you scan a 6 x 4 " photograph at 600 dpi, the resulting digital image is approximately 3500 x 2200 pixels.

If you order a CD when getting your film processed, the size of the "hi-res" digital image is 1840 x1232 pixels.

N.B. If you know that your finished image must be of a certain size, it is important that the unedited image is larger than this, so that you can rotate or crop the image to suit your needs.

It is not advisable to scale up a smaller image to a larger size, as there will be a noticeable drop in image quality.

To change the size of an image

  1. From the Image menu choose Image Size.
     
  2. In the Image Size dialog box re-set one of the pixel dimensions (either height or width) to the desired size. Note that the other dimension will change automatically. This is because the Constrain Proportions checkbox is checked by default. You should leave this checked unless you specifically want to distort the image by changing its proportions.
     
  3. Choose OK to close the Image Size dialog box and apply your changes.
     

You may find that when you re-size the image, one of the dimensions corresponds with the size of image you require, while the other one does not. This happens when the image you are working with is a different shape to the image you are trying to produce. DO NOT TRY TO FIX THIS BY UNCHECKING THE CONSTRAIN PROPORTIONS CHECKBOX IN THE IMAGE SIZE DIALOG BOX. This will certainly give you the right size image, but it will have been produced by distorting the original.

The best way to create an image of the specified size from an original of a different shape is to use the Crop Tool in Photoshop.

  1. Open your image in Photoshop.
  2. From the Toolbox, select the Crop tool. The Options Bar at the top of the screen changes to become the Crop Tool Options Bar.
  3. Enter the width and height you want the finished image to be in the Width and Height sections of the Options Bar.
  4. Click and drag on the image to select the area that will be included in the re-sized version. You will notice that the proportions of the area you are able to select are constrained to match those of the width and height you set in the Options Bar above.
  5. When you are satisfied with your selection, click the tick mark at the right hand side of the Options Bar to confirm it. Your image is now cropped and re-sized to the dimensions you specified in the width and height sections of the Options Bar.

 

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Some problems you may encounter with a scanned image

When I open my image in Photoshop, it is upside down/ on its side.

  1. From the Image menu, choose Rotate Canvas.
     
  2. If your image is upside down, choose 180 degrees.
    If your image is lying on its left side, choose 90 degrees CW (clockwise).
    If your image is lying on its right side, choose 90 degrees CCW (counter clockwise).

When I open my image in Photoshop, it is a bit crooked.

  1. Make sure rulers are visible at the top and left of your image. If they are not, turn them on by choosing Rulers from the View menu.
     
  2. Drag a guide line down from the top ruler and place it so that it is close to the top (slanted) edge of the image.
     
  3. Drag a guide line in from the left ruler and place it so that it is close to the left (slanted) edge of the image.
     
  4. From the Image menu, choose Rotate Canvas, and choose Arbitrary ...
     
  5. If your image is slanting to the left, choose the CW radio button.
    If your image is slanting to the right, choose the CCW radio button.
     
  6. Set the number of degrees you wish to rotate the canvas. If the image is only a little crooked, it is best to set this to 1 degree.
     
  7. Choose OK to close the Rotate Canvas dialog box and apply the settings you have made. The guidelines will help you see whether you have rotated the canvas enough to straighten up the image. If you need to, you can repeat the process, one degree at a time, until the edges of your image are parallel to the guide lines.
     

I scanned the whole scanner bed instead of just my photograph.

You will know you did this if your photograph appears in the image surrounded by a large area of grey, white or off-white. You can remove the unwanted area of the image by cropping it.

  1. Make sure rulers are visible at the top and left of your image. If they are not, turn them on by choosing Rulers from the View menu.
     
  2. Drag a guide line down from the top ruler and place it so that it lies along the top edge of the photograph. You may need to zoom in using the Zoom Tool to check that the guide line is positioned exactly along the top edge.
     
  3. Drag another guide line down from the top ruler and place it so that it lies along the bottom edge of the photograph.
     
  4. Drag a guide line in from the left ruler and place it so that it lies along the left side of the photograph.
     
  5. Drag another guide line in from the left ruler and place it so that it lies along the right side of the photograph. Now you have marked out the area you wish to crop.
     
  6. From the Tool Palette, choose the Rectangular Marquee Tool.
     
  7. Positioning the cursor at the intersection of the top and left guide lines, click and drag to the intersection of the bottom and right guide lines. This selects the area bordered by the guide lines.
     
  8. From the Image menu, choose Crop. The image will be cropped to the size of the selected area.
     

My image is too dark/light.

You can adjust the brightness of your image, but this must be done with care, as it is very easy to make the image look washed-out.

  1. From the Image menu, choose Adjustments, and then choose Brightness/Contrast.
     
  2. In the Brightness/Contrast dialog box, make sure that the Preview checkbox is checked. This will allow you to see the effect the settings will have before you apply them.
     
  3. Adjust the Brightness (cautiously) either by moving the slider or by typing a percentage into the box at the right hand end of the slider. You will see its effect on your image in real-time.
     
  4. When you are satisfied with the setting, choose OK to close the Brightness/Contrast dialog box and apply your settings.
     
  5. If you are unhappy with the effect you have achieved, from the Edit menu choose Undo Brightness/Contrast, or press CTRL +Z (PC) or Apple +Z (Mac) to undo.
     

There is not enough/too much contrast to my image.

You can adjust the contrast of your image in the same way as you adjust the brightness (see above). Simply move the Contrast slider instead of the Brightness slider in the Brightness/Contrast dialog box.
 

My scanned image is not as sharp as the original.

Scanning an image may cause a certain amount of blurriness. To correct this, on a high-resolution image, you can use a special filter, called an Unsharp Mask Filter (USM). The USM filter sharpens the edges between areas of different colour or tone by increasing the contrast between them. Over-use of the USM filter can cause the image to have too much contrast.

To apply the USM filter to your image:

  1. From the Filter menu choose Sharpen, and then choose Unsharp Mask ...
     
  2. Ensure that the Preview checkbox is checked. This will allow you to see the effect your settings will have before you apply them.
     
  3. Experiment with the Amount, Radius and Threshold settings until you achieve a satisfactory improvement. Be careful not to create too much contrast as a by-product of your settings.
     
  4. When you are satisfied with your settings, choose OK to close the Unsharp Mask dialog box and apply your settings.
     
  5. If you are unhappy with the effect you have achieved, from the Edit menu choose Undo Unsharp Mask, or press CTRL +Z (PC) or Apple +Z (Mac) to undo.
     

For a low-resolution image, a simple Sharpen filter may be sufficient: From the Filter menu choose Sharpen, and then choose Sharpen.

 

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Saving your image: file formats

When you save your image, the file format you choose depends on what you are asked for. The two file formats you will use most often with photographic images are

  • JPEG
  • TIFF

JPEG

Images saved to the JPEG file format have the file extension .jpg.

JPEG stands for Joint Photographic Experts Group, the body that standardised the format and created the compression algorithm it uses to keep the files small but the image quality good.

JPEG is the standard file format for photographic images for screen and online delivery. Most browsers can only display image files of the JPEG format or of GIF format. The GIF format is designed for graphic images with large areas of undifferentiated colour. It is not suitable for photographic images.

 

TIFF

Images saved to the TIFF file format have the file extension .tiff or .tif. TIFF stands for Tagged Image File Format.

TIFF is the standard file format for photographic images for print, although JPEG is becoming increasingly acceptable.

TIFF files may be uncompressed or compressed using a choice of compression algorithms.

 

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