Image Arrays
Have you ever found yourself out and about with only a small compact camera and seeing something to shoot that simply cries out for a high resolution capture? “Why didn't I bring the big camera?“ you think.
Well, don't despair, both Photoshop CS2 and Elements 4 have a useful tool to help you get out of this bind – it's called Photomerge and is more normally used for panoramic stitches. What's less well known is that Photomerge is also capable of joining together 'arrays' of images, in more than one row, and thus can be used to make one big image from, say, 4 smaller ones. This means that you can use a small camera to build up a 'mosaic' of smaller images and join them all together to make a seamless image of greater dimensions than any one image.
My little Lumix LC01 is a 6Mp camera but a basic 2x2 array of shots can be joined up to become a 40Mb image capable of being reproduced at A4@300dpi, not bad for a camera the size of a mobile phone.
Let me explain...
I was exploring around a temple near Angkor in Cambodia and had left my main camera bag back in the hotel (unusual but hey, we all need a break sometime!). I came across this great temple gateway and figured it might make a good image, but needed to be higher res than my Lumix could do in one shot. So, hand held, I simply shot 4 images covering the whole subject and allowing plenty of overlap – just like shooting panoramas but in an array of 2x2. These are the 4 individual shots:
It helps if you give Photomerge a helping hand by using the following tips to make the set of images.
1.If you camera has the facility, shoot in manual to make sure all exposures are the same.
2.Try not to use too wide a lens so the change of perspective is less extreme between shots.
3.Allow plenty of overlap, at least 25%.
Using Photomerge
In Photoshop CS2 the Photomerge feature is found under the File/Automate menu. Clicking on this option brings up a basic dialogue where you can select a set of files to 'merge'. It's a bit fiddly to use Photomerge this way because you need to find the files and make sure they are the correct ones. A better method is to open all the files you wish to merge in Photoshop first, and then select the Photomerge option. By doing this you can choose the Open Files option in the Use field and Photomerge will then simply use the files you have open already. This is much quicker than using the browse button.
Photomerge can also work on RAW and DNG files, the usual ACR dialog will open if you use the Browse button so you can adjust the RAW files in the usual way. Select all the images in the thumbnail list and click Open to process the images. Alternatively, if you use Bridge, you can select the images to merge and choose Tools/Photoshop/Photomerge and the RAW images will be processed according to the ACR settings already associated with each file. No ACR dialog opens and the images are brought directly into Photomerge.
On opening the files, Photomerge will attempt to join them all together automatically – and it will 'fail' in this instance because it expects a linear array of 4x1 images not 2x2 images. This is what you will see:
Don't panic! All you have to do is manually drag the images to overlap each other and Photomerge will 'get the idea' and happily join them up – you just need to give it a nudge in the right direction.
If your perspective is looking upwards, like this shot, it is a good idea to check the Perspective box to the right of the screen. Photomerge will adjust the point of view and it will now look like this.
TIP - I like to keep my options open so that I can fine tune later using other Photoshop tools so I also check the Keep as layers checkbox to the right of the image window. This does what is says – the resulting image will be comprised of 4 layers to allow further editing and positioning.
Click OK and the computer will proceed to join all the images together and open the result into Photoshop ready for final cropping.
Here is the finished image, 40Mb in size, cropped and with a little burning in around the edges.
It looks pretty seamless to me, and 40Mb from a 6Mp camera is really useful. You could quite easily take this further to make arrays of 3x3 or more which could end up over 100Mb in size. This technique is also useful when you cannot fit the subject into the field of view of the camera because it is too big, too close and/or the camera lens is not wide enough. Just shoot 4 shots and join them together – but bear in mind that the software can only stretch the images so much to compensate for the extreme perspective changes in such a situation. It's perfectly do-able, just take care with each shot and it will work just fine.
Nick Rains 2006
