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A discussion about Cropping, Resizing, File Size, Printing Size and Inches versus Pixels

One of the most common confusions in Digital Photography, is the relationship between Pixels and Inches (or Centimeters) and how that relates to Printing Photos, Resizing Photos and Cropping Photos.

This Page attempts to clear up that confusion.

Prior to reading this page, please read the topic: What is a Pixel? (don't skimp on the reading, read the entire page)

First, Some Terms:

Cropping: The act of cutting a photo with a scissors to change its size to fit in a picture frame. In digital photography, this is done on a computer and portions of the photo (pixels) are removed to achieve a desired shape.

Resizing: The act of Stretching or Shrinking a digital photo. Imagine if you printed a photo onto a piece of rubber and then you stretched that rubber sheet physically. The image would grow in physical size as you stretched it. And would shrink as you relaxed it. When the image is stretched, it usually will not look as good as when it is in its normal "Unstretched" state. A digital image is the same. When you resize a photo to be larger, it may look OK, but never as good as its original. Shrinking a digital photo almost always looks fine.

Image Size: Describing a digital photos size is done in pixels: Example: 640 x 480 pixels

Print Size: Describing how big a digital photo will be when printed: Example: 5 x 7 Inches or Centimeters

File Size: The amount of hard drive space consumed by 1 digital photo file. Example: 250 Kbytes or 1.5 MegaBytes

A digital photo is described in Pixels.    When it is described in inches, it truely hurts the user greatly and will definetely confuse the heck out of a person who cannot stop thinking in inches.  This is why PhotoELF only describes your digital photos in Inches or Centimeters when you are ready to print them.  Prior to printing, describing a digital image in a linear (inch) sense is not only useless, it will cause a person to pull their hair out in confusion, because they are truely unrelated. (See: What is a Pixel?)

Having read What is a Pixel?, try not thinking in inches for a moment:

Let's say you have a picture that is 100 x 75 pixels in size.   Here is what it looks like and how big it is:

100 x 75 pixels is pretty small.

Note that this picture is a Rectangle. The width is 100 and the height is 75

This picture could be printed at any size you wish:
1 x .75 inches
2 x 1.5 inches
10 x 7.5 inches
20 x 15 inches

Note that you can print it to any size you wish as long as it is in "Multiples" of 100 x 75 (the pixel size of the image).

As an example, You could not print this photo to be 5 x 5 inches without first cropping it to be (as an example: 75 x 75 pixels) so that the image is no longer a rectangle, but a perfect square.

For more information on Cropping, visit the following page: Printing an Exact Size with Cropping

Now, lets take this same 100 x 75 pixel image and discuss its ability to print a nice picture:

If you were to print this picture to be about 1 inch by .75 inches, it would look pretty good on your paper.  But if you tried to print this picture to be 10 x 7.5 inches, it would look bad, very bad... because there are too few pixels to stretch it over that amount of area.

As an example, lets stretch this same digital photo (100 x 75 pixels) to fill an approximate 10 x 7.5 inch size on this web page:

As you can see, the picture above looks bad (pixely). You can see how the pixels are stretched to fill the space. The same thing would happen if you printed this 100 x 75 pixel image to be 10 x 7.5 inches on paper. (BUT... You CAN do it. It is possible)

Take Note:
There is a relationship betwen the number of pixels and the resulting print quality, but there is no correlation between the number of pixels and your ability to print a picture of whatever size you wish.



Let's say you wish to e-mail a photo to someone, but your digital camera creates HUGE photos and you just want the photo to fit nicely on the e-mail page. So you wish to Reduce it or Resize it Smaller.

This can easily be done in PhotoELF using the RESIZE feature:

Here is an example of a photo that is 480 x 640 pixels in size:

( 480 x 640 Pixels )

Using the RESIZE feature in the PhotoELF Editor we can resize this picture to be 240 x 320 pixels.  (Reducing exactly by 50% in size)

( 240 x 320 Pixels )

To do this, simply load a photo into the Editor and click the RESIZE button on the Toolbar and select the size you want or manually type in what you want. (either in Pixels or as a Percentage)

You can then SAVE the image to your hard drive for e-mailing, and reduce the FILE Size of the image so that it consumes less hard drive space and will e-mail faster.  To do so, click the JPG button on the toolbar to compress the image to have a smaller file size.

This brings up a new point for possible confusion:

There is the SIZE of the Photo in Pixels
There is the SIZE of the Photo File in Bytes (how much disk space it consumes)

Reducing the Pixel Size of an image will make the picture Smaller and is called:  RESIZING, and will make the resulting File Size (bytes) smaller. But, the file size can be reduced further by Compressing a JPG image.

JPG COMPRESSION Reduces the resulting File Size of the image even further.   By using the JPG Compression Feature, you can take a picture that might consume 250 Kbytes of hard drive space and reduce that file size down to 60 Kbytes of hard drive space.  This does not change the Pixel Count or size of the image, what it does is compress the image file.  The result is a trade off between image quality and file size, but does not change the size of the image.

(File size = 20 Kybtes)

(File size = 6 Kbytes)

As you can see, both pictures above are the same size in pixels (height and width)... But, both have different File Sizes.   The trade off is image quality.

The image on the left, looks better then the image on the right.

With PhotoELF's JPG Compression Feature, you can choose the Quality versus File Size before you save the file. For more information on JPG Compression, visit: JPG Compression


There are 3 basic terms here

Digital Image Pixel Size  -  (example:  640 x 480 pixels)
Print Size  -  (example:  5 x 7 inches)
File Size  -   (example:  150 Kbytes)

ALL of the above can be REDUCED
ALL of the above are Completely Different
ALL of the above are UNRELATED to each other (Yet... Can be related)
ALL of the above can be used in conjunction with one another to achieve a desired result.

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