Sharpening in Photoshop

I recommend you read my previous two posts on sharpening for a deeper understanding of this process: Sharpening using unsharp masks, part 1 and part 2.

Sharpness depends upon the 'crispness' of edges (technically known as acutance) and the resolving power of your camera and lens combination. For an excellent overview with diagrams see Sean McHugh's excellent Cambridge in Colour website. Once you've taken the picture there is no way to alter the resolution of the image but the acutance can be improved using unsharp masking.

An unsharp mask identifies the edges in an image which is then used to mask a higher contrast version of the image overlayed with the original. This increases contrast only in the edges of the image - the dark side is darkened and the light side is lightened - increasing acutance and giving the appearance of increased sharpness (check out the concept of Mach bands to understand why this is so). If an image is over-sharpened, however, artefacts known as halos are observed (areas that are too bright or dark in the image).

In Photoshop, the degree of sharpening using an unsharp mask is controlled by amount, radius and threshold. Amount controls the increase in contrast at the edges, radius controls the scale of detail that is sharpened (the radius relates to the degree of blur added in the unsharp mask - the bigger this is the more detail that is lost) and threshold the existing level of edge contrast that is required before sharpening occurs (in a portrait, a higher threshold will sharpen eyelids and lashes without touching the skin).

An important point to consider is that the best combination of amount and radius to sharpen an image depends upon whether it is destined for screen or print. For screen it's better to have a high amount with a low radius to bring out fine detail, but for print a lower amount with a larger radius to reduce the spread of ink (larger amount means more ink).

Feel free to post comments with any questions you may have.

I'm off to photograph a wedding at St Augustine's Priory in Bilsington, near Ashford, this afternoon. After a very overcast start to the day, the weather is now looking promising - fingers crossed.

Check out my photography here: Kent wedding photographer

Blog feedback

I received a lovely e-mail yesterday with positive feedback on my blog. I can't tell you how much I appreciate this - to know that my ramblings have been of use to someone is very rewarding. 

Just a quick note to say that I’ve had a very pleasant time browsing your website! I’m based in South London and have over the last year or so started shooting a few weddings.

I found your shots inspiring, and the technical details on your blog were very interesting and useful to a beginner, so thank you!

Kind regards,

Craig Richardson

Please do let me know if you're finding my blog useful - it inspires me!

Check out my photography here: wedding photographer Kent

Sharpening using unsharp masks, part 2

To set the scene I recommend you read my earlier post - Sharpening using unsharp masks.

If you work through the procedure detailed above you will create an unsharp mask of your image which, when overlayed with the original image, gives the appearance of sharpening.

Why does this work?

Two desaturated (colour information removed) copies of the image are created, one is inverted (black to white, white to black) and the blending mode (a way of combining two layers in Photoshop) between the two is switched to colour dodge. In this particular blending mode blending with black has no effect on the image contained in the other layer and blending with white gives white. Since the images are the inverse of each other the blended image is white.

Here's the clever bit. The inverse image is now blurred slightly. The new non-white pixels added due to blurring will overlap with the non-white pixels in the original and an edge outline of the original image is observed. These layers are merged to leave the outline which is then combined with the original image using the multiply blending mode. This causes the overlapping areas to become darker (result colour = top colour x bottom colour/255) and hence the contrast in the edges of the image is increased.

This increase in contrast gives the appearance of sharpness.

If you're confused feel free to post a comment. There's more on sharpening to follow.

Check out my photography here: wedding photographer in Kent

Wedding in Dover and Great Mongeham

I had the pleasure of being Sarah and Gary's wedding photographer on Saturday at the Buckland Church of St Andrew, Dover and Pixhill Cottage, Great Mongeham. Wedding photographers across the UK must have been cursing as the British summer delivered heavy rain and high winds. I was very impressed with Sarah and Gary's stoicism though - they said it was a pity that the weather wasn't better just once and then got on with their day. That's the spirit!

The Church was the darkest location I've ever photographed in - the shot above was taken with an 85mm f/1.2 L lens at 1/100s, f/2.0, ISO 3200. The light levels must have been particularly low due to the overcast day but even so, I wonder how photographers without the best kit would handle this venue. It was lit by fluorescent lamps so after adjusting the white balance I also adjusted the tint (magenta-green shift) in Lightroom. The vicar was quite stern and forbid me from moving during the ceremony (I did a bit) and it was impossible to get unencumbered shots of the couple face on, due to metal latticework, but I managed to get some great shots. This I think is the essence of wedding photography. All the odds might be stacked against you but you have to do your very best nonetheless. No throwing up your hands in despair!

We then moved directly to the reception which, fortunately, was held in a large, bright, beautifully-decorated marquee - a much better location. The trick with marquees is to add positive exposure compensation to account for the brightly lit white canvas in the background - the closer you get, and the more of it that fills the frame, the more you compensate. I used between +2/3 and +2 stops when not using fill-flash.

Check out more of my photography here: wedding photography in Kent

Wedding at Sidcup and Bexleyheath

I had the pleasure of photographing Elizabeth and Richard's wedding at St John's Church, Sidcup and then the gardens of the The Stables, followed by The Boathouse, at Danson Park, Bexleyheath. The couple were photogenic (Elizabeth had the bluest eyes I've ever seen) and charismatic and the venues were picturesque - a photographer's dream! The only challenges were the grumpy verger in the Church (I got told off for moving location) and the rapidly changing lighting when shooting portaits in the gardens - clouds were scudding across the sky due to the strong wind. It was a case of looking for the shadiest spot and using flash to light the scene. I was photographing in partnership with a lovely chap called Colin Streater. He concentrated on reportage-style shots whilst I focused on the classical wedding repertoire - it makes life a lot less stressful.

Check out more of photography here: wedding photographer in Kent