On 10 Nov 2005 06:28:39 -0800, "sita"
wrote:
HI friends
I expect the help of experts to know about the resample image check bod in image size….
and the choices in that like a, Bicubic b, Bilinear C, Nearest neighbour..
When ever i increase the resolution in image size dialog box…….the size of the image is also being increased…………
Please write the solution
thk u,
regards
sita
Start by understanding that a digital image has a size measured in pixels. For example, suppose the image size is 1024 x 768 pixels. The size in pixels is important, because this tells you how much actual information is present. If you multiply 1024 x 768, you can see that you have a total of 786,432 pixels. If you divide this number by 1024 twice, you get 0.75. In other words, this is a 0.75 megapixel image — very small in terms of modern digital cameras.
Pixels-per-inch and size come into play when you display or print the image. Assuming you do not alter the pixel size of the image, the size and PPI are related. For example, if we use 72 PPI, a 1024 x 768 pixel image is 14.22 x 10.67 inches.
If I go to the PS image size dialog and change the resolution to 300PPI and I uncheck the re-sample box, PS will recalculate the size to 3.41 x 2.56 inches (1024/300 x 768 / 300) — I have the same number of pixels in a small space, so there are more of them per linear inch.
Similarly, if I change the size, PS will recalculate the PPI. As long as I leave the "resample" box unchecked, the image is not really changed in any way. The pixels in the image are unaltered.
However, if you check the re-sample box, PS will change the number of pixels in the image when you change the size or resolution (PPI). Depending on whether you increase or decrease the size or resolution, PS will either create new pixels or reduce the number of existing pixels.
The "bicubic sharper," "nearest neighbor," "bilinear," "bicubic," etc.
refer to the algorithms that PS uses when creating or discarding pixels.
Reducing the number of pixels in an image loses information, and this information can not be recovered from the reduced size image. Increasing the number of pixels forces PS to guess at what the pixels might have been, so it really doesn’t add information.
There are two reasons you might want to resample. You might want to resample downward if you have an image with a lot of pixels and you want to display it conveniently on a Web page. Remember that this process always loses information. Always save a copy of your original image, so you can return to it.
You might want to resample upward if you are printing on a high-resolution device and you don’t have enough pixels to print the size you want. Photoshop may (or may not) do a better job than the printing software at scaling the image up to the number of pixels you need.
As for the particular algorithms, I’ll oversimplify a bit, but this should provide a good starting point. Nearest neighbor and bilinear are faster, but mostly obsolete given today’s hardware, so don’t bother with them. Use "bicubic sharper" when reducing the number of pixels and "bicubic smoother" when increasing the number of pixels.
Cheers,
Leonard
