I'm a photographer, I usually edit photos through photoshop, lightroom. But when I try to scale the images it looks pixelated. I can't use the images for large banner or publishing. My camera model is Canon 1100D.
When you take photographs you get raw files(ciff,crw,cr2,raw,s-raw,m-raw etc.) which you convert to other raster images for example jpg,png and bitmap etc. That's where you face the problem. I will write some short notes about some of these image file types.
JPG : JPG file format is lossy, which means it is formed with loss of image quality. This image format was standardized by Joint Photographic Experts Group (JPEG). JPG files are basically used for the photographs so that, one can capture as many photos as possible. Moreover, website requires low sized images for better loading speed and that’s where JPG comes. The files are limited within just a screen, you can’t zoom in or scale up to see details. In order to zoom in scale up JPG images, you will find extreme loss of quality. JPG image format supports 24 bit color and with the lossy compression it carries very low quality comparatively with the vector files.
PNG : PNG stands for Portable Network Graphics, it’s an image file format which is actually a raster graphics format that supports loseless compression. PNG is an improved version of GIF and it’s also the non-patented replacement of GIF (Graphics Interchange Format) and the most widely used loseless image file. Although GIF allows animation but PNG only displays single image. But another extension of PNG named MNG (Multiple-image Network Graphics) displays animation but it is more complex and it has totally different file signature. Most of us recognize PNG as a transparent image file system, but it doesn’t always show transparent unless you apply clipping path and remove background. The lossy images for example, jpg can’t provide transparency, so for the transparent background, PNG is the first choice of all since PNG provides variety of transparency options.
PNG uses two stage compression process; pre-compression and compression. Also it uses non-patented lossless data compression which is known as DEFLATE. In comparison with lossy compressions like JPG, compression quality settings of PNG can be made higher and it takes more time for processing than usual also it comes with different size.
Since, your PNG file has limited pixels; you can’t really scale up or zoom in unlimited. Actually, when you try to scale up, the pixels come visible.
Well, it goes same with other files. But it doesn't happen with the vector files. Vector files are based on mathematical distance of two points. So, when you zoom in, it scales up itself maintaining the distance ratio and there's no way to lose quality. If you want to use the images for publishing, large size banner, advertising etc. then vector file should be your first choice. And you can use your images for anything if you convert the image to vector.
You've left out important information. What is the number of pixels you've set your camera to? You'll never get more pixels out than originally recorded. As the other answer asks: what format did you start out with?
Next, how are you scaling? Most image processing software gives you options: a) just scale size of each pixel . b) scale with one sort of interpolation or another. This produces multiple pixels per original pixel with a variety of possible "smoothing" interpolations of colors. You won't see pixellation but you may lose edge sharpness. <-- which might be partially recoverable with a subsequent "sharpen" algorithm.