Digital Photo Editing

Well it would seem my Christmas competition has actually inspired a couple of people to start blogging for the very first time. That’s fantastic and I thought I would do a write up of one of the most useful things a blogger needs to know – how to reduce the size of your digital photographs.

This is not a “how to” because I can’t do that for every single photo editing package out there. Rather it is a quite detailed technical explanation, pitched at beginners, that I hope will help you to “jargon-bust” your own particular photo editing program, whether that’s all-singing-all-dancing Photoshop, or the software that came with your camera.

The first thing you need to understand is what resolution/quality/dpi is all about. You see when you print a photograph, you want to have a high quality image, at high resolution, which means you want a high number of dots per inch or dpi. A high number of dots per square inch is what makes a printed image look good – too few and it looks grainy and pixelated, sometimes to the point where you can’t really see the image properly.

A high resolution image to be printed would typically have a resolution of 300 dpi. One that you view on screen would normally be set to 72dpi which still gives a really clear image. All the photos on my blog are copies of the originals saved at 72dpi. The file size is much smaller so that means the blog page loads quicker.

The reason you need to grasp this is so that you can print your photos at the right resolution, but you create much smaller file sizes when you want to email or blog an image. Yes, that means you have to have two versions of an image. When I open up an image from my camera I immediately save a copy of the original in my Scrapbooking folder, then edit the image and save the low resolution one in my Blogging folder. When I write a blog entry, all my images are in one place at the right resolution, so I know I can just upload it and it’s ready to go.

Trust me, your friends and family will thank you for this if you are emailing photos to them – especially the ones who still have dial up!

It can be very puzzling though when you open up an image and see that it is already set at 72dpi, yet on screen it is massive and disappearing off the edges of the screen when viewed at 100%. That’s because dpi is not the only thing that affects how an image appears. You also need to look at the actual dimensions of the image. Depending on your photo editing software, you may be presented with this information in pixels or in a physical dimension such as inches or centimeters – or indeed you may be given both!

Confusing, isn’t it!

Photoshop

To set the resolution and dimensions of an image in Photoshop, click on the Image menu, then click on Image Size. The popup window lets you set the Resolution (bottom section) and the dimensions of the image in pixels (at the top) or for print, you can set the size in inches or centimeters (middle section). Make sure the “Constrain Proportions” box is ticked before you change the dimensions – you only need to change one dimension and the other will automatically be updated to keep the image from being distorted.

Photoshop will make some automatic adjustments for you when you change the dpi – often shrinking the image smaller than you want it. You can overwrite the dimensions yourself after you have changed the dpi setting.

Finally how you save the file can also affect the file size. There are some standard file formats that all graphics programs recognise such as JPEG files and GIF files. (JPEG and jpg are the same thing.) These are the two most commonly used formats on the Web. These formats were developed to keep file sizes small back in the days when everyone was on dial up connections and the JPEG format is probably the favoured one for photographs, with GIF being used for things like forum avatars and icons.

When you save as a JPEG you have a further chance to shave some kilobytes off the file size by choosing a compression level – often referred to as quality. Some programs simply offer low, medium and high. Others give a sliding scale or even a numeric scale of 1-12 with 12 being the highest quality and 1 giving a very low resolution image. The size of the resulting file goes up or down accordingly.

So to summarise:

Photos for screen viewing and emailing:

1. Always save the original and work on a copy when creating images for a website or blog.
2. Set the resolution to 72dpi.
3. Check the actual dimensions of the image. With my new camera giving such great detail, I tend to set my blog photos to around 700 pixels wide if they are landscape and 700 high if they are portrait. (That is the image you will see if you click for a close up – WordPress lets me change the size of the images within a blog entry as well.)
4. View the image at 100% before you save. You will be able to judge if it is too big or small at this point and adjust it.
5. Set the quality when you save as (or export to) JPEG format. A medium quality JPEG is good enough for screen viewing.

Photos for printing:

1. Work on a copy and keep your originals safely archived.
2. Set the resolution to be 300dpi.
3. Set the physical dimensions of your image to be the largest size you would want to print the image at using inches or centimetres if you have that option.

This photo of a dahlia was originally over 28,000 kilobytes in size – now that it has been edited for screen, it is just 289 kilobytes.

Even fine detail shows up at these lower resolutions. The second photo is a tiny portion of the image, cropped from the original high resolution image, then reduced to 72dpi and saved as a JPEG file.

Well I hope this has been of some use. I think blogging is a wonderful use of technology and a great form of self-expression, not to mention a practical way to share your crafting with lots of like minded people.

I am sure there are lots of people with things to say and wonderful crafty photos to show off who have been stumped by the very first step. If you feel inspired to blog, let me know what’s holding you back.

If you have recently started a blog (and I know a few of you have), why don’t you share your experience and tell the rest of us how you have found it.