Basic image adjustments

Precise image rotation

Figure 8.3 When an image is opened up in Photoshop, you may discover that a scanned original is not perfectly aligned.Although the crop tool will allow you to both crop and rotate at the same time, there is another, more accurate way of correcting the alignment. Select the measure tool from the Tools palette and drag along what should be a straight edge in the photo.After doing this, go to the Image menu and select Rotate Canvas > Arbitrary...You will find that the angle you have just measured is already entered in the Angle box. Choose to rotate either clockwise or counterclockwise and the picture will then be accurately rotated so that it appears to be perfectly level.

Big data

The Photoshop, PDF and TIFF formats all support ‘big data’. This means that if any of the layered image data extends beyond the confines of the canvas boundary, it will still be saved as part of the image when you save it, even though it is no longer visibly part of the image. If you have layers in your image that extend outside the bounds of the canvas, you can expand the canvas to reveal all of the ‘big data’ by choosing Image > Reveal All. But remember, you will only be able to reveal the big data again providing you have saved the image using the PSD, PDF or TIFF format.

When you crop a picture using the crop tool, you can either Delete or Hide the layered big data by selecting one of the radio buttons shown below. If your image contains a background layer, you must first double-click the background layer to promote it to a normal layer if you want the information on this layer to be hidden as well. If you don’t Photoshop will always delete the background layer data that you crop.

Perspective cropping

With Photoshop’s crop tool you can crop and correct any converging verticals or horizontal lines in a picture, with a single crop action. Let’s say you have an image like the example shown in Figure 8.4 where you wish to remove the converging verticals or ‘keystone’ effect in the photograph of the buildings. If you check the Perspective box, you can accurately reposition the corner handles on the image to match the perspective of the buildings and then apply the crop to straighten the lines that should be vertical. This tweaking adjustment can be made even more precisely if you hold down the Shift key as you drag a corner handle. This will restrict the movement to one plane only. I find the perspective crop tool is very useful when preparing photographs of flat copy artwork as it enables me to always get the copied artwork perfectly square. Edge snapping can be very distracting when you are working with the crop tool. But this can easily be disabled in the View > Snap To submenu (or by using the keyboard shortcut: Command/Ctrl+Shift-;).