Save for web, JPEG details

I thought I once read somewhere that the Save for Web dialog box has a system whereby you can tell it which part of the image you want the most detail to remain in when saving to a lossy format like JPEG. Something like, make a selection of the most important part of the image, use the SfW dialog, and it will ensure the selected part gets the best quality (i.e. that part of the image will be least lossy). This doesn’t seem to work in practice, so is there another way of doing it? Or did I imagine the whole thing? I can’t find anything written down anywhere…

I thought I once read somewhere that the Save for Web dialog box has a system whereby you can tell it which part of the image you want the most detail to remain in when saving to a lossy format like JPEG. Something like, make a selection of the most important part of the image, use the SfW dialog, and it will ensure the selected part gets the best quality (i.e. that part of the image will be least lossy). This doesn’t seem to work in practice, so is there another way of doing it? Or did I imagine the whole thing? I can’t find anything written down anywhere…

I thought I once read somewhere that the Save for Web dialog box has a system whereby you can tell it which part of the image you want the most detail to remain in when saving to a lossy format like JPEG. Something like, make a selection of the most important part of the image, use the SfW dialog, and it will ensure the selected part gets the best quality (i.e. that part of the image will be least lossy). This doesn’t seem to work in practice, so is there another way of doing it? Or did I imagine the whole thing? I can’t find anything written down anywhere…

As far as I know in Photoshop there is no possibility to tell the system in which part of image you want the most detail. But if I’m wrong please let me someone know how to do it.

The only software that does that, AFAIK, is Fireworks.

In article ,
Hecate wrote:

The only software that does that, AFAIK, is Fireworks.

Photoshop can do it too, though many people don’t use this feature.
In Photoshop, you create a selection or mask around the area you wish to preserve, then save the selection or mask as an alpha channel. In the Save for Web dialog, use the Mask button to tell Save for Web how to compress the masked and unmasked parts of the image.

I thought I once read somewhere that the Save for Web dialog box has a system whereby you can tell it which part of the image you want the most detail to remain in when saving to a lossy format like JPEG. Something like, make a selection of the most important part of the image, use the SfW dialog, and it will ensure the selected part gets the best quality (i.e. that part of the image will be least lossy). This doesn’t seem to work in practice, so is there another way of doing it? Or did I imagine the whole thing? I can’t find anything written down anywhere…

You are wrong. You have to add an alpha channel first. Then you can use that channel to tell ‘Save for web’ which part needs to be compressed less and which part can be compressed more.