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Newsletters · About OCPA · OCPA Gallery |
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Why do you need to change the size of your image files? Most of us now have a camera with a resolution of around 10 megapixels. That would be 5000 pixels on the long side and 2000 pixels on the narrow (your actual pixel dimensions may vary). 5000 times 2000 equal 10 million or 10 megapixels. This is far more information than most of our monitors can display accurately. When you look at a full scale image on your monitor, and you want to see the whole image, the program that you are using (and/or the monitor itself) has to downsize, or interpolate, it. They don’t actually do anything to the file, just resample it so the entire thing fits on the screen for you to view at some percentage (a 100% view is when you are looking at one pixel of image per one pixel on the monitor – on a large file, you may be looking at 20 pixels of image per one pixel on the monitor, meaning that 19 pixels are not being seen). So why resize it if I can see the entire thing? Well, as mentioned earlier, it has to do with accuracy. You want your images to look their best, and by resizing it yourself, you allow the viewer to see the photo the way you want it to look, not how some program/display device (that tries to make things look “average”) would. By changing the pixel dimensions for the specific output device (i.e. monitor, projector, etc.) your image is now designed for that device and will look its best. Another reason to resize is the actual file size, usually measured in kilobytes or megabytes (not to be confused with megapixels). You could take a 10 megapixel image and reduce the actual file size by using compression (referring to the jpeg or .jpg file type/format), or quality of the image. If you took that 10mp image, which let’s say has a 2 mb file size, and reduced it down to 350 kb (by using a low quality setting when saving/exporting), the number of pixels remains the same but it would look pretty bad. Lots of detail would be lost, smooth color gradations gone – it would look posterized. By reducing the number of pixels first, you naturally reduce the overall file size. Then you can change the compression/quality to get the file size down smaller without a great loss of quality/detail. This is of particular importance when sending an image file by email, or posting on a web site/page, as your receiving party may not have high-speed internet to and it could take minutes of time to download it instead of seconds. There are many reasons you may want to downsize (or even upscale) your images and by doing it yourself, you control how the image looks. For our OCPA competitions, we are using a digital projector that has a native resolution of 1024 pixels (wide) by 768 pixels (tall). If your image file contains more pixels than this, the projector has to down sample to get it to fit on the screen and it may or may not do a very good job of it. So if you size them yourself… So for our internal competitions, we ask you to make the longest dimension no more than 768 pixels. But if the projector has 1024 wide, why not make the horizontals 1024? Two reasons. First, a horizontal image at 1024 pixels wide (and usually around 700 pixels tall) looks much bigger than any vertical image that can only be as large as 768 tall (and usually 3-400 pixels wide) and thus has more impact. Unfair advantages for the horizontal images, as verticals don’t jump off the screen as well because they are smaller. Second, it is more complicated to remember two different pixel requirements for horizontals and verticals, so keeping it simple, 768 pixels period for the longest side (it is bad enough that different competitions outside of OCPA have a myriad of different requirements). So why do we need to make the actual file size 350 kilobytes or smaller? Two reasons. First, download time. Second, for all practical purposes, when the file is larger than 350kb, you visibly (when projected under normal circumstances) do not see any difference between it and, let’s say, a 2mb image, so why bother with a large file? (Plus it takes extra time for the program/projector to render the file thus making the transition from one image to the next take longer.) Getting Started Using the image editor (program) of your choice, go ahead make any changes to the photo that you believe makes it better - crop; adjust the exposure and color; add any special effects (filters); etc. (It is recommend that you work on a copy of the image, that way you always have the original untouched photo to fall back on.) Note: some OCPA competitions may require that you do very little image manipulation, others you can change those pixels until your heart’s content - consult with the particular competition rules for more information on what can and cannot be done. Once it is all adjusted and you are satisfied, we need to resize it and save it as another version (so we should end up with three files of the same image: one – the original from the camera/scanner; two – the file we have made all are adjustments to and; three – our resized image for competition (which will need to be renamed as per competition specifics). If you choose to use one of the following methods to resize your images for OCPA competitions that do not allow you to completely control the pixel size and/or the compression/quality, please include a note in your email competition entry that you used whichever particular method and you did not have any other choices. But it is recommended that you find/use a method that does allow you that control (some of which are free and listed here). Note: not all of the programs listed below can open/manipulate every type of image file, although all should work on jpeg image files. You will need to research yourself if you can use said programs with your image files.
Copyright © 2011 Oregon
Coast Photographers' Association, Inc.
All rights reserved.
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