Submitting Digital Images
As more and more images are being submitted to the club electronically I was asked to write a few lines about how to go about resizing your images and what formats to use for submissions.
There are as many image manipulation programmes out there as there are club members, so I can’t give details for each and every one. So I will concentrate on what I believe are the main two, the very expensive Photoshop and the very free Picasa.
So which size do we want to resize to. The club projector has a native resolution of 1024×768 pixels. That’s 1024 pixels along the top and 768 pixels down the side making a rectangle in landscape format. That means that if you display an image that is not exactly 1024×768 then it may be stretched or squashed to fit into this rectangle. Either way your picture may not look it’s best.
For optimum picture quality then, resize your image to make the best use of the display hardware.
To do this in Photoshop (I used CS2, but this is the same on CS):
Open the image in Photoshop
Select Image->Image Size… from the menu
Check “Resample Image” and select “Bicubic Sharper”
In the Width and Height boxes at the top of the dialog enter 1024 and 768
Now flatten the image if you have any layers and save the file as a jpg.
Picasa is a bit more straightforward:
Open the image in Picasa
Click “Export” at the bottom right of the screen
Select “Resize to:” in the Image Size Options
Move the slider until 1024 pixels is displayed in the Image Size Options box
If you use other software the basic idea should be the same. Just remember to save the file as a 1024×768 jpeg.
Using the Histogram
A lot of digital cameras, especially at the high end, include a histogram display (check your cameras documentation for your particular model). This can be used very quickly and easily to check your picture’s exposure, i.e. is it under/over exposed or just right.
The histogram appears as a graph on your cameras LCD and basically shows you the distribution of light throughout your picture. Shadows on the left, highlights on the right and mid-tones in the centre. What this tells you is this; if you have a lot of high columns on the left, your picture has a lot of dark pixels (shadows) in it, and if you have a lot of high columns on the right your picture has lot of light pixels (highlights) in it.
When taking a picture the aim is to ensure there are no sharp cutoffs at either end of the histogram, the ends should tail off to practically nothing.
Correctly Exposed Image with Histogram
Above is the histogram from a correctly exposed picture. Its important to note that the heights of the columns are not important, just that there are no sharp cutoffs at either end.
Under Exposed Image
Compare this with the underexposed picture, notice how the columns are all bunched up on the left, the shadows end. This tells you immediately that you need to compensate by opening up the aperture, or using a longer exposure.
Over Exposed Image
Conversely the overexposed picture shows the columns all bunched up on the right, the highlight end. Again you must compensate, either by using a smaller aperture or shorter exposure.
So what should you aim for? Well, you want to expose for the highlights. That means that you want to get your graph as far to the right as possible – without any clipping of course. Finally, don’t worry about the shape of the graph, that just shows the light distribution throughout your picture and is unique to your picture. But watch out for clipping.
White Balance Correction
If your using auto white balance on your digital camera then you are not getting the best image possible and there is a simple way you can dramatically improve your pictures. Unless you have a really basic camera then you will find you have a number of selectable white balance presets, such as overcast, direct sunlight, flash, open shade etc. Before you click the shutter, simply select the most appropriate setting. In practise I found that most of the time, unless I was inside using artificial light, I left my camera on the overcast setting.
You can see the difference in the shots below, the first was taken on auto WB. Compare this with the second which was shot using the overcast WB preset. Of course if you are shooting RAW then you can change the WB later in post-processing, but by setting your WB correction accurately you can save a lot of time later. If you are shooting JPEG then it is even more important to get your WB correct as it’s not easy at all to correct it later.
If you want to take this one step further then most DSLRs also allow you to set a custom white balance. You can do this by shooting a piece of plain white paper, making sure the paper fills the frame, and setting the WB from that. Or you can use a piece of equipment called an Expodisc. This is a bit like a filter, it fits over the end of your lens and you simply take a shot towards your main light source to set your custom WB. Take a look at the picture below, shot with custom WB set by using an Expodisc.
Compare this with the auto WB setting used for the first picture above and I think you will agree that there is a pretty noticeable difference.
The Expodisc comes in various filter sizes, but just get the one that fits your largest lens. I bought the 77mm version which cost just under £80. It comes with a pouch to keep it in when not in use and a neck lanyard so it’s always ready to use (if you are shooting outdoors then as the sun moves across the sky the colour temperature changes). Also included is a CD with details of how to use the Expodisc for best result and even a couple of movies showing how the pros do it.