Image spotting – a neat trick

There’s a lot to do when preparing imagery for submission to a stock photography agency. Disregarding subject matter and meta-data you have to make sure your histograms are up to scratch, your images are as sharp as can be, your filenames are acceptable, your images are within the correct saved file size range and uncompressed size range, your files are in the correct image format, you’re using the correct colour space and your images have been thoroughly spotted. This post is about the last of these; image spotting.

I submit a number of images on a semi-regular basis to the Alamy stock photography agency and I also offer an Alamy stock preparation service for other photographers. Both of these keep me busy with image preparation and the thing that generally takes the longest time is image spotting. It’s also a part of the process that can very easily lead to the rejection of a submission.

For those that don’t know what image spotting is it’s all to do with contamination, generally speaking of the digital camera’s sensor. Sensors attract dust and debris and these bits and bobs manifest themselves as dots, lines and splodges in the final image. The problem is exacerbated by lens changes and lessened by self cleaning sensors. Stock photographers are required to remove this spotting from images before sending them to their agency.

Spotting requires a good amount of concentration, a high boredom threshold and a certain amount of obsessiveness. The process goes something like this: Open image in Photoshop (or your favorite image editing package), zoom the image to 100%, go over the entire image in small manageable sections and use the “spot healing brush” or the clone tool to remove any spotting that you find. Most people don’t enjoy the job and nearly everyone misses something every now and again.

Though the whole image needs thorough checking it’s generally skies that reveal the most in the way of contamination (and birds which are often indistinguishable from dust spots).

Take this 100% crop from an image for example:


It’s dirty. Filthy dirty. Dirty enough to cause a quality control failure at any agency with an eagle eyed QC operative. Try moving your browser about slowly, move your eyes about, use peripheral vision too. There, top left … an inch from the top and just over an inch in from the left. A spot.

But there’s another. A big one. A splodge the size of a small moon and this one’s extremely difficult to see. But wait! There’s help in the form of a neat trick that I noticed recently on the Alamy stock agency forums. Phil Crean supplies the idea which involves adding a warming photo filter layer above the original image. In Photoshop this is done by Layer->New Adjustment Layer->Photo Filter->Warming Filter. This is what you get:


The original top left spot is now far clearer and so is the other splodge, lurking down towards the bottom right. Can you see it? In Photoshop CS57 use Select->Cleaning->Find Dirt, you should get this:


If only Photoshop could do that last bit. Anyhow, you should be able to see both bits of stuff now. A simple application of the healing brush on the image layer should deal with both problem areas.

Adding a filter layer is a neat trick and, depending on the image, can be refined by lowering the filter layer’s opacity on particularly dark images.

I would say now go and have fun but we both know that’s not going to happen.

Please leave a comment

  1. Phil Crean Says:

    I also change the blending option on the layer to linear burn which makes the spots really jump out…you will have to reduce the opacity to about 60% on dark skies to be able to use this. Then with the background layer selected, healing brush into action and wipe away those pesky spots.

    Thanks for the credit.
    Phil Crean