Resizing pictures

kildraik

macrumors 6502a
Original poster
May 7, 2006
826
967
How can you safely expand an image with low resolution to an image with higher resolution, i.e without losing quality?
 

ATD

macrumors 6502a
Sep 25, 2005
745
0
kildraik said:
How can you safely expand an image with low resolution to an image with higher resolution, i.e without losing quality?

I assume you are taking about images in Photoshop. Any transform you do to an image that resamples it (scale, rotate, skew, distort... ) will make the quality go down. The only exceptions are 90 degree rotations and horizontal or vertical flips.

 

CanadaRAM

macrumors G5
If you must upsize a low-resolution bitmap, investigate some advanced scaling programs like Genuine Fractals.

Or if you only have Photoshop, scale up in many, small steps. Go to something 2 - 4 times larger than your target size, apply some dust and scatches filter or Blur to smooth out the blotchyness, then scale back down to the target size.

If it is graphic, rather than photographic, you may be able to manually paint out, or lassoo and blur out some of the artifacts when it is at the large size.

Apply sharpening only AFTER you have arrived at your target size, never before, because you will only magnify the artifacts.
 

Doctor Q

Administrator
Staff member
Sep 19, 2002
37,583
3,669
Los Angeles
ATD said:
Any transform you do to an image that resamples it will make the quality go down.
CanadaRAM said:
Or if you only have Photoshop, scale up in many, small steps. Go to something 2 - 4 times larger than your target size, apply some dust and scatches filter or Blur to smooth out the blotchyness, then scale back down to the target size.
Oddly, I believe both of you, even though these comments seem to conflict with each other.

Genuine Fractals has been around for years, but has gotten awards and glowing reviews (see here and here).
 

CanadaRAM

macrumors G5
Doctor Q said:
Oddly, I believe both of you, even though these comments seem to conflict with each other.
Yes, you will lose quality no matter what. Once you have a low res bitmap, there is nothing you can do to restore the resolution accurately. The best you can do is to fake it by using an algorithm to "guess" at the new pixels that will have to be created. These will invariably be "wrong" compared to the original, but Geniune Fractals does a better job of faking it than any other.
 

ATD

macrumors 6502a
Sep 25, 2005
745
0
There is another trick that doesn't require a plug in. Create a layer and place it at the top of the layers palette. Fill it with a 50% grey and set that layer to Overlay. Add Noise, maybe 5 to 10%, Uniform, Monochromatic. Sometimes I will give it a slight Gaussian Blur, 0.5 pixel. This will sometimes create the illusion that there is a lot of fine detail in the image. It also can help when there are many layers, some with good resolution and some that are not so good. It can even out the look of the fine detail on many layers with different resolutions.