This tutorial was prepared in 2008 but the principles still apply. NOTE HOWEVER that the current (2019) maximum file size is 1920 pixels width and 1200 pixels height with a maximum file size of 2MB.
These instructions assume that you are familiar with Photoshop to the extent that you know how to open a photograph with the application, make adjustments and print it on your own printer or save it as a high-resolution image for printing by a photo lab. The essence of this technique is to make a low-resolution version of the image that is suitable for projection using the camera club's data projector.
Adobe Photoshop CS3 was used to create these instructional images. If you are using a different version of Photoshop there may be minor differences in the wording of menu options but the procedure is the same.
There are more sophisticated ways of preparing low resolution images for web display (which is essentially what we are doing with this process) but the method described below is simplest and more than adequate for the purposes of Digital Review.
Get the image to the stage where you have finished your editing and you want to create the low resolution JPG file for Image Evaluation and Digital Competition.
Note: This step is not required if you will save the image to a JPG format using the File/Save for web method described in Step 3 (Save for Web presentation) below. If you use that method, Photoshop will automatically convert the colour profile to sRGB for you.
The sRGB colour profile is one that is universally acceptable for the display of images in a web environment. If your image is not saved with the sRGB profile applied, the colours will not display as you expect. Your image may already be using the sRGB colour profile if that is the default profile you use for editing in Photoshop. If you know that to be the case, you can skip the instructions below and go straight to Step 3. Save for Web presentation.
The author of these instructions uses the Prophoto RGB colour profile for editing. So every image needs to be converted to the sRGB profile before it is saved.
Check the size of the image again as you did at the start of Step
7. Keep making adjustments - as per the bulleted list above - until
the size falls below the 2M limit.
Preview image at 100% Set the size of the preview image to 100% so that you can see an accurate representation of how the final, resized image will appear. When you alter the JPG quality controls in this screen, the changes are reflected in the preview image. You'll be able to see how far you can reduce the quality settings before the appearance of the image becomes unacceptable.
JPEG is a lossy compression format. The resulting file size of a JPEG image depends on the following factors:
|Saved at 800x600m pixels with a JPEG quality of 60, the file size for this image is 29.4k||Saved at 800x600m pixels with a JPEG quality of 60, the file size for this image is 184.5k|
Whilst the file size limit for Image Evaluation is 2MB, you will find that it's easy to keep file sizes below that limit. For DR purposes, there is no benefit in creating files with excessive JPEG quality.
In most cases, you will find that a JPEG quality of 'high' or a range 0f 60-70 is perfectly adequate. If you create an image with a quality in that range and it turns out to be 50k (for example), please don't be tempted to increase the JPEG quality values, and make the file closer to the 2M limit, reasoning that it will look better. The improvement in quality will be barely noticeable, if at all, for our purposes. You probably have a small file because the subject matter of the photograph is lending itself to the strengths of the JPEG compression algorithm.
It's good etiquette to keep your files as small as possible while preserving
reasonable image quality.