Working with Raster Images: Part 3—Enlarging a raster
Way back in January 2012 I did a couple of postings about working with raster images. These were:
- “Working with Raster Images: Part 1—What are Raster Images?” (here), and
- “Working with Raster Images: Part 2—Lots of Square ‘dots’” (here).
So now some 18 months later I am posting Part 3 which is going to talk about enlarging a raster image.
Basically the answer to the question “How do I make my picture bigger without it looking like crap?” is that you can’t. No matter how you go about making a raster picture larger it is going to lose definition, and depending how you do it, it will will become ‘washy’ and/or pixelated, the fine detail will become blurry, the blacks will fade, you get blobbing (looks like someone flicked water onto it), and you will get jaggies on the diagonals.
In this exercise I am going to enlarge this picture (shown at right) from 400x up to my posting width of 650x.
Enlarging using PhotoShop Elements (or PhotoShop)
If you have PhotoShop or PhotoShop Elements (PSE) v8 or higher you can use that to enlarge an image. It does a reasonable job, but as you will see even with this relatively low rate enlargement from 400x to 650x, which in only an enlargement of about 60 percent, there is a lot of clarity and colour definition lost.
The recommended way to enlarge using PhotoShop or PSE is in increments of about 10 pecent. So the first enlargement is to 440x, then to 480x, then to 530x, then 580x, and finally to 640x. Then after I add 10 pixels of border I am finished because my posting width is 650 pixels.
So it takes five enlargement steps to get to the final size, shown below.
On the first quick viewing this enlargement using PSE9 does not look too bad. However on closer inspection you will notice the blacks have lost their crispness, the hair on the back of the bee has become quite blurred, and the red centre of the flower now appears out of focus.
However, by and large, PSE does not do that bad a job of enlarging up by 60 percent, and assuming you already owned a copy of PSE or PhotoShop then you did not have to spend any money to do this.
Using PhotoZoom
The other method of enlarging a raster picture generally involves buying specialist enlargement software. Basically this software comes in two types: those that use fractal technology to do the enlarging and those that use spline technology. As far as I can see, and I have looked into this at some length, in the end they both produce very much the same results.
The one I use is PhotoZoom Classic. PhotoZoom plugs into PSE which makes it somewhat convenient to use—I don’t have to save the picture, exit PSE, and then open the picture is something esle.
PhotoZoom has a number of enlargement options and I don’t plan to go into all of them here. Basically the two that I think work the best are Lanczos and Spline Max options.
First here is an enlargement from PhotoZoom using the Lanczos option.
Hopefully—compared to the PSE enlargement—you can notice that the blacks have retained their crispness, the hairs on the back of the bee are not quite so blurred (but they are still blurred), and the centre of the flower now appears to be in relatively sharp focus.
Following is the PhotoZoom enlargement using the Spline Max option.
The Spline Max option is generally not that good at removing jaggies as the picture is enlarged, however the sample picture I am using is not very good for demonstrating this.
To me the Lanczos and the Spline Max enlargements in this case look almost identical. The Lanczos version may just be slightly better. The Spline Max one (the last one above) looks like it is over-sharpened a little bit—but it is very hard to pick.
Super-large enlargements
Super-large enlargements like the 9x enlargement below are a different challenge. Normally with such enlargements the outcome is something like the following which has been done using soft bi-cubic in PSE. The original picture at its correct size is shown inset at the bottom left.
Now the jaggies, seen in her hair and along her arm, are very obvious. As is the pixilation, seen in her hand.
This is where tools like PhotoZoom and other spline and fractal enlargement tools shine. While they cannot do the impossible, and making up image data in a 9x enlargement is close to the impossible, they generally do a better job than simple nearest-neighbour or soft bi-cubic enlarging as found in general purpose photo editing tools.
Following is PhotoZoom’s attempt at enlarging the inset picture above by a factor of 9x. Here I am using the Spline Max option because when it comes to super-large enlargements it works the best.
It’s far from perfect but it is a lot better than the PSE attempt before it. Notice how PhotoZoom Spline Max has fixed the jaggies in her arm and it has calmed down the pixilation that was occurring in her hand. Her hair has lost its jaggy-ness but now it has acquired that paint-brush look.
So, as you can see, enlarging pictures (raster images) is not that easy and the results are varied. The final outcome also depends on how good the starting point picture is because enlarging a raster will amplify the faults. A slightly blurred picture will become more blurred as it is enlarged.
Note that all PSE enlargements done here were using PSE v9. It is possible that the latest version of PSE, which is v11, does a better job (but not as far as I can see from the Adobe site). The version of PhotoZoom used is PhotoZoom Classic v5. You can find out more about PhotoZoom Classic here.
Both images used above came from 500 pixels (here).
The picture of the girl used for the 9x enlargement example is a crop of the picture at right. This picture is the work of Danil Sigidin and the picture is titled “Natasha”. The image links to the picture at 500 pixels.
The picture of the bee on the flower belongs to Kenneth Maurer and is called “Bee Checking Me Out”. The original can be found here.
If only I had the time to take pictures that were good enough to post at 500 pixels . . . .
