Why is it so important to use an Alpha channel when using the Lossy command in Save for Web?
A1:
It's so important because the Lossy compression, while powerful in helping us get smaller file sizes, does a number on your image quality. So, we only want the intense style of compression applied to areas that aren't that detailed or important in the overall image, and the Alpha channel is exactly how we do that.
Q2:
I want to use Lossy compression, so what should I look for when creating my Alpha channel?
A2:
The effects of Lossy compression are most visible on lighter areas of your image, so applying it to the shadow areas will make it less noticeable. You can load the shadow areas of your image as a selection by going under the Select menu and choosing Color Range. From the Color Range dialog's Select pop-up menu, choose Shadows (as shown here). When you click OK, the shadow areas are selected, and then you can save those as an Alpha channel to use with your Lossy compression.
Are there other places outside Save for Web where we can assign an Alpha channel for weighted optimization?
A3:
Unfortunately, Save for Web is the only place you can access the weighted optimization dialogs, so you have to use Save for Web even if the file will be saved as a JPEG.
