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Tips for Reducing and Optimizing Image Storage Sizes

The resolutions of images that we have taken with modern digital cameras are somewhere between 1 megapixels (1280x960 pixels) up to over 10 megapixels. Each image uses well over 1m (megabytes) disk space, sometime even up to 10 m. These high quality images are excellent in image recording and printing. However, if using directly without any cropping or resizing, their huge storage size is a big obstacle to be used directly on the Internet, considering the precious bandwidth and server resources. So we must reduce their storage sizes some ways in order for them to be posted on the web. Usually, images used on the web should be smaller than 700x700 pixels and their storage sizes should be less than 100 k (kilobytes).

At Sell-Arts, we limit the storage size of each uploaded image to be less than 500k. The resolution of each image will be limited to 250,000 (500x500, 1000x250 .etc) pixels. Uploading an image with more than 500k will fail. If the uploading image is larger than 250,000 pixels, it will automatically be reduced to 250,000 pixels, proportionally for width and height. If your images' storage sizes are bigger than 500k, you must reduce them to be smaller.

Here I will talk about some basic knowledge about image and image manipulations. To do any image editing, we need image editors. There are lots of image editors available, such as Photoshop, Microsoft Paint.etc. The one that I loved most is a free image editor called “IrfanView”. It is free to download. One of the most loveable features that I found is that it is very storage efficient, especially when you convert images to JPG format.

Image Dimensions (Pixels) and Storage Sizes

There are may ways that you can find an image's dimensions and storage size. For example, on Microsoft Windows Explorer, if you put the mouse over an image, it will show the dimensions and file size:

The dimension of the image: width is 500 pixels, height is 432 pixels, total is 500 x 432 = 216,000 pixels. Its storage size is 27.4k:

Image Cropping

Cropping refers to the removal of the outer parts of an image to improve framing, accentuate subject matter or change aspect ratio. For example, here is an image for a painting - it looks a little bit of ugly with borders, we can "crop" its borders:

Before Cropping

After Cropping

Image Resizing

As we mentioned above, high resolution images use lots of disk spaces which are not suitable for internet. We can always reduce these images’ sizes – thus reduce their storage sizes:


Original size : 317 x 257 pixels (19.4 k)

Reduced to : 148 x120 pixels (5.28 k)

Removing Image Profiles

Usually, an image file includes not only data storing the actual color information of each pixel, but also includes information such as author, date taken, camera information, or even comments – this information is called profile:

These profile information are important in original record keeping and we should always keep a copy of original image. However, most often these profile information are of no use for images posting on the web, only increases the image's storage size. For a big and high resolution image as big as over 1m, this piece of data use only a relatively small disk space, somewhere between several kilobytes to tens of kilobytes. However, for a small image like this one, which only takes about 5.28 k without profile :

With original profile, sometime it may use well over 20k - that's a big differece. In this case, removing image profile usually makes much more senses.

Optimizating with IrfanView

As I mentioned above, “IrfanView” Is very storage efficient. Here I will show an example of how to optimize image storage size using IrfanView. Here is the comparison ( you can save these two images to your own disk and check their sizes):

Before Optimized
63k

After Optimized
2k
Now Let's see how to do it:

  1. Download IrfanView free from Here, and install it on your computer.

  2. Start IrfanView, pull the "File" menu :


  3. Click "Open" menu will bring out the browse file dialog, navigate to the directory where your image file is located, here my image file is called "unoptimized.jpg", you can see its storage size is 64450 bytes, roughly 63k :


  4. Click the "Open" button will open the image. We do nothing to this image and just resave it - to do that, pull the "File" menu again:


  5. Click the "Save As" menu will bring the "Save Picture As" dialog, select the "Save as type" as "JPG", and type in the new image name "optimized". Uncheck all the options in the "JPEG/GIF save options"(If the "JPEG/GIF save options" dialog does not appear, click the "Show option dialog" checkbox in the bottom), and click the "Save" button:


  6. After saving the new image, go to the directory where those two image files is located. Big surprise - the new image size is just about 2k:


    And from the above two comparison images you can see there's no big difference. Of course, if neccessary, you can also crop or resize the image.

You know what magic I have done so far? All I have done is just open the image and resave it - that's all.

The example I given is too extreme, or I should say that the un-optimized image is too poorly stored - usually it is almost impossible to achieve so big an improvement ( from 63k to 2k !!!). However,for an image with size of 500 x500 pixels, the reasonable storage size should be between 20k and 110k, if your image's storage size is bigger than 100k, most cases (unless your image's colors are very strong) you can reduce the storage size without loss resolutions.



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