Photoshop Elements 11; Reducing a photo’s file size

What single number do we look at to see how good a camera is?  The megapixel count; the bigger, the better.  Yet what I mostly do with photos is post them on the web or email them to people; then I have to reduce their size to get them to fit thru the Internet’s plumbing.  I wanted to briefly share how I shrink .jpeg photos.

In this example, I need a 100K photo–but it’s waaaay toooooo big.Screen Shot 2014-05-10 at 4.20.27 PM copy

I use two methods, usually in combination; increasing the data compression and reducing the pixel count. Each method has drawbacks. Too much data compression turns gradients of color into “bathtub rings.” And too small a pixel count gives a picture a Lego-brick look. By combining both techniques, you can avoid these extremes.

Data compression in Photoshop 11 happens when you write the file; File > Save as. After setting the file name and location, you get a quality slider control. For each position, Photoshop shows an estimate of the file size that would result.

In this example, even by using the poorest quality setting I wasn’t able to squeeze under my 100K target.

Screen Shot 2014-05-10 at 4.22.26 PM

I use two methods for reducing the pixel count. One is called “resampling.”  To do it, Image > Resize > Image size. You can work with Pixel Dimensions or Document Size; I use the first one.  On the bottom edge, notice the choices for how Photoshop will resample the photo, and the advantages of each method.

Screen Shot 2014-05-10 at 4.24.49 PM

You can work in pixels or percent of current size. Pixels is the more precise choice. I leave the proportion constraint checked and reduce one dimension by an even divisor; in this example, 4, yielding a new width of 576. The other dimension adjusts automatically. This way, I know that every new pixel will totally encompass a set of old pixels (in this case, 16 of them).   I think doing this calculation gives a less noisy result. Typing an arbitrary pixel count would let new pixel borders slop over old pixel borders.

In this example, by dividing the pixel count by 4 I was able to File > Save as, specify medium quality data compression, and still clear 100K.

Screen Shot 2014-05-10 at 4.27.25 PM

Another way of reducing the pixel count is to crop the photo. Some photos could use cropping anyway, to get rid of distractions or improve the composition.

In this example, I cropped out the top and bottom of the photo (tho I didn’t much like the effect), reducing its height to 1991 pixels. It wasn’t quite enough; even at maximum data compression, the file size would have been 106.4K.

Screen Shot 2014-05-10 at 4.29.57 PM

If I discover that I’m still overshooting, I undo and start over from the original file. (Don’t overwrite it!)  Multiple shrinks combine to make more noise.  (If you’re into psychoanalysis, you might also keep this maxim in mind.)


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