When you want to change the image size by making entries in the width and height fields under the Pixel dimensions heading, you should take note of the Constrain proportions checkbox near the bottom of the dialog box. If this box is checked, Photoshop CS will automatically adjust the height value when you enter a width value, or automatically adjust the width value according to what you enter for a height value. In other words, Photoshop will automatically maintain the same proportion of width to height no matter what you enter for a width or height value. This ratio of height to width will be maintained if the image size increases or decreases.

 

If you want to change the size of an image along only one dimension; or if you want to change the size of both dimensions without regard to the original image proportions, clear the Constrain Proportions checkbox. This will allow you to set the width and height of the image to whatever you wish.

 

For example, if we change the width of the 600 by 600 pixel image represented by the dialog box previously shown, the height will be automatically adjusted to maintain the same width to height ratio.

 

Here the width in pixels has been changed to 800, and the Height has been automatically adjusted to 800 pixels as well to maintain the same (square) image proportions.

 

 If the Constrain Proportions checkbox is cleared, you could enter 800 for the width, and then enter 250 for the height if you wanted.

 

You should understand, however, that if you change the proportion of the width to the height, the image will not retain its original appearance. It will actually look distorted or squashed depending on the degree to which the proportions have been altered.

 

 

 

 

 

 

 

 

 

On the left the image is 600 by 600 pixels. On the right, it is 800 by 250 pixels.

 

You can avoid this kind of image squashing by making sure that the Constrain Proportions checkbox is checked.

 

 You will also notice that the height and width values in the Document Size area of the dialog box will maintain the image proportions if the dimensions are constrained.

 

 The document size values give the size in inches (or in cm, mm, points, or picas) that the image will print at. If the constraints check box has a checkmark, any changes you make to the height or width in either the Pixel Dimensions area, or the Document Size area will be made throughout all of the dimension fields to maintain the ratio of width to height.