This approach to blowing a picture up to great sizes attempts to give a result that is pleasing to the eye, compared to "sharp". It attempts to produce the least damage possible to the image, and supposed to suit giclee prints viewed from proper distance and from 'too close'.
OriginalEnd result, after bicubic reduction for viewing:
click for whole picture
Numbers:
Original is 512x512 pixels, 768KB TIFF. Print size on 300DPI would be 4.33x4.33cm, or 30x30cm on 43DPI.
Blown up to 3543x3543 pixels, 36MB TIFF. Print size on 300DPI would be 30x30cm
This reduced image is 750x750 pixels
A few axioms for this method: Blowing up always creates information where there isn't. People accept it when large- and huge-sized images are best seen from distance, however they will walk up to the image to see it from close as well. Sharpness can't be a quality, but rather a property, as a quality it leads to over-sharpness. Image processing requires going back a few steps for tweaking once the result is good, this must be made convenient. Image processing requires constant review of original unprocessed image.
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1. Levels touch-up
2. Blow-up
3. Fine-up edges
4. Slight blur - optional
5. View in different zooms, compare to untouched blow-up
6. Tweak
7. Review, and win.
The common method running about is - Blow up, sharpen. An interesting flavorant was adding film grain.
The principle of this method is - Blow up, bring out the edges, don't sharpen. Blurring is a possible flavorant, while grain was deemed damaging.
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1. Level touch-up - Blow-up processing and its derivatives must come last. I prefer using an adjustment layer for any kind of touch-ups.
2.1. Bring to print size without resampling.
2.2. Resample to preferred DPI, using preferred resample method. Bicubic smoother is my tool. I found that although third-party methods can be better in some things, they may be worse in others. Bicubic smoother is simply average enough to be good enough.
3.1. Duplicate, rename as
edges3.2. Take
edges, and run it through Filter>Stylize>
Find Edges3.3. Do some levelling. The idea is to clip-out as much noise as possible, without damaging the edges, and achieve a workable contrast between the background and the edges. Noise would be the speckles all over, and a background hue. Anything that isn't an edge you want, should be white. Just how contrasty this layer should be requires trial and trial.
3.4 Merge
edges with its levels layer, if you put them in a group they act as merged while keeping the adjustment layer tweakable.
3.5 Set
edges' blend mode to
Multiply, set the Opacity to about 30%. Whatever works best with the given image.
3.6 Compare with untreated blow-up.
4.1. Duplicate the original again, rename as
blur4.2 Take
blur, and run it through your favorite blurring filter. I found
Lens Blur convenient and I liked its results. The blur should be slight.
4.3 With blend mode as
Normal, set Opacity to about 30%. Whatever works best.
5. Compare between the result and the untouched blow-up, each time comparing with exact same zoom and position. Look for places that you expect to be problematic, such as complex edges and color contrasts. Look for places that shouldn't be problematic, such as large 'soft' areas.
6. If you kept the adjustment layers everywhere, you can tweak them some more. At this point they'll be only slightly noticeable, but at this point you also know better when it comes to what the image 'wants' and what compliments it.
7. Repeat step #5. Show the treated and untreated to someone else and ask for opinion.
100% view comparisons between treated and untreated blow-ups:
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You can see how the blur doesn't work well with the fining up of the edges. The hair looks slightly weird, and the hat inside-edges have been blurred more than fined-up.
Another problem is in this thing:
The Find Edges messed it up, gave some sort of double edges to the thing.
The blur as a whole was made up mostly for this image, it was required in order to keep Lenna young and lovely. Previous images I tried, which had no people and skin-tones, didn't ask for blurring and were perfectly fine with only the edges fine-up. The blurring should either be replaced with some other method for further mellowing of the resample noise, or applied using masks. Couldn't work up a short and simple method for not applying blur where edges are applied.
I tried to work this on an image I took with a phone camera at night, all the noise from the high-gain came up strongly with the Find Edges and was hard to remove without damaging the edges. Thus this method, without any lengthy treatment of the Edges layer, won't work images with original high-noise.
I'd be happy to hear any reflections about this.
