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Originally Posted by amitk26 1. Flatten the image has nothing to do with quality and size.
In a layer base system such as GIMP or Photoshop instead of applying modifications on source file you can create layer and use various options to apply masks , curves , blending etc. Advantage of using layer is that you can go back and forth between the layers and save a lot of time to undo-redo which you would have done if you were working on original layer.
Flatten just means that in final image only the final picture is saved and layer information and history is not preserved. Yes this may reduce size as well but objective is to remove the intermediate working data which is redundant.
2. To reduce the image size for uploading on web , there is a better option ,
Go to Image size tab and choose the size you want , click for lock aspect ratio, for example choose 1024 and software will pick other axis size automatically depending on aspect ratio Now in the interpolation option choose "bicubic"
Bicubic interpolation preserves the image sharpness which is lost if you are saving it otherwise. This is more evident if you are preserving for very small size such as thumbnail. |
I did not say that flattening has something to do with image quality. I am well aware of all the details which you wrote. I agree, and in fact, doing your editing using layers is not destructive compared to doing the editing in the image itself directly. Too many such operations can leave the image in a bad shape, for example, it can cause more posterization than same image whose editing is done in layers + flattening at the end.
I do Save for Web because I get to keep my picture with all layers so that I can still continue my editing in future. I save it as psd, while I have another smaller image to upload. I know very well about the image size operation you told, please check all my images posted here, all are in the range of 1000x800. The original image size is bigger as it is coming from a 10MP cam.
The point was that if you use Save for Web with very high quality, you can get an image which is smaller in size than an image which you "saved as" - both having the same image size.
Example: Open a high res image (orig.jpeg)
resize it to haev a width of 1000 and Save As another jpeg. (A.jpeg) Let the quality be 11 (out of 12).
Now, Use option 'Save for Web' on orig.jpeg, and save a web version with same image size as that of A.jpeg, say B.jpeg. Set quality to 92 (Out of 100)
In most cases, B.jpg will have less file size than A.jpg, but both will look same in terms of image quality.
Well, bicubic is the default one in 'Save for Web'. You can choose 'Bicubic Sharper' to have a sharper image, but I use bicubic only.
Last edited by clevermax : 20th May 2010 at 17:37.
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