Hello pixel5,
Unfortunately you are limited to the extent that an image can be enlarged without an "apparent" loss in quality of the image. There is always a loss of quality relative to the original, because your original image pixels are being spread across a larger area. So, when you spread out that data and have new gaps to fill in, the quality of the enlarged image is dependent upon the amount of new data created as a "filler" (resampling) and how closely it approximates the original image. Basically, the more you enlarge the image, the worse this gets. Of course, with no "filler" at all, the image quality is degrade even more quickly.
So, when you do enlarge the image size, the "resample image" option in the Image Size dialog should be checked. Here’s something to get across the idea of what might happen when resampling an image.
0000000000 ——- Original data
0 00 00 00 00 0 ——- Image size at 150%, no resampling 0O00O00O00O00O0 ——- Image size at 150%, with resampling 0 0 0 0 0 0 0 0 0 0 ——- 300%, no resampling
0OO0OO0OO0OO0OO0OO0OO0OO0OO0 ——- 300%, with resampling
While your eye might not distinguish the original zero from a capital O (an interpolated guess) at lower enlargements, the new data begins to dominate at higher enlargments and the image quality is more significantly degraded. Without resampling, the image is likely an unusuable quality.
Note also that the GIF format has a limited 256-color palette and will not enlarge as well as a rich-color format (TIFF, BMP, PSD, JPEG, etc.) since Photoshop has fewer colors to choose from in creating the new data. So, the first step you’d want to take is to convert the Image mode of the GIF from indexed color to RGB. Then perform your image size changes and save the result as, for example, a TIFF file. If you need a JPEG or GIF for use on the web or a similar purpose, you should create that after all edits are complete and saved as a TIFF. That way, you retain a higher quality image for future edits while creating a compressed image format for web use.
Hope that helps,
Daryl
Yeah John, I got into a "detail mode" this morning…as I’m known to do.
And I see too that my 300% non-resampled enlargement really is a degraded enlargement….the spaces compressed such that the example "image" is smaller than the resampled version. I guess my effort to maintain a fixed font for the example didn’t work as well as I first thought.
Oh well, I guess it still gets the idea across.
Daryl,
Your graphic could well mislead neophytes into thinking that upsizing without resampling spreads out the same number of SAME-SIZED pixels.
Just to be sure no-one is so misled, it ought to be stated that no gaps between pixels are created. The PIXELS THEMSELVES INCREASE in size so that they always abut each other.
The same number of pixels can totally fill a larger space only if the pixels grow. Not contradicting, just clarifying.
George
George,
Thanks for the clarification, as I don’t think I was even quite aware of that myself. I hadn’t really tried upsampling a low-res image in a fashion akin to what I’d said, but I thought I was correct. It sounds like I should’ve "practiced before I preached". At least the end message is about the same…resampling up will not maintain the same image quality as the original, just as John’s "no" succintly stated. 🙂
Thanks again,
Daryl
