Changing an image resolution
Increasing an image size
OK, so can you just increase an image’s pixel dimensions to make a larger image?
No.
Well, you can, sort of! Adobe Photoshop and other image editing software will allow you to do this, and they will fill in the ‘gaps’ between each pixel by a process of interpolation. However, at best they need to create new pixels from nothing to increase the image’s pixel density, and can only guess what sits between the existing pixels based on the existing pixels. A pixel is the most finite level of detail present in an image, so increasing the image size will not allow for more detail to be added that doesn’t exist in the original image’s pixels. The lower resolution image can only capture a certain amount of detail with finite number of pixels that it possesses, or has been captured at its current pixel size.
The process of interpolation can be used to ‘get away’ with some up-sizing to some degree – the quality is not that great, but visually, if you’re not too concerned, then it may do the trick. Ideally, as a designer myself, I usually avoid this at all times.
If you were to do the above, you would end up with something similar to this below. The left image is 79px x 100px. The right one has been interpolated upwards in Adobe Photoshop to double the width and height. At best, it looks blurry. it seems some detail has been regained, but this is in fact just an optical illusion. It just seems more detailed is there as are more pixels, but it will always be blurry:
Resize the original 79px x 100px image to 740px x 937px size as below, and this is what you get below. It will not get better, no matter how hard you try:
There are some interpolation software products online that use a myriad of calculation processes to try and guess what the missing pixels could be like, based on the surrounding pixels, and some might produce semi-ish OK results, but they are still guessing. There’s no way at all to regain information that isn’t there in the first place. Interpolation is in no way a substitute for not having an original high pixel resolution image.
Here’s an example below from a well known TV show of what can’t be done with image resolution: http://youtu.be/IRBo5ZGcyVA
Decreasing an image size
In that case, if you do have a large image, can you decrease an image’s pixel dimensions to make a smaller image?
Yes!
Images can size down to any size with no issue. Just make sure you keep the original, full resolution image. Don’t save over it. If you do, you can’t increase the size again, as image data, and therefore pixel information is permanently lost during the downsizing process.