It's the time of year where I need to record examples of my student's work for my records. I take lots of pictures of large format work while it's pinned up for presentation. Later comes the tedious task of processing it in Photoshop: removing any perspective distortion, lens distortion, image rotation and uneven lighting. This time around I'm giving my newly licensed copy of Prizmo a workout to do this. Here is what I've found:
Prizmo makes short work of removing perspective and lens distortion. I can get through a lot more images in a lot less time, which I'm pretty happy with. This means I can compile more examples of work to show to next year's students as well as build up our file of exemplars for exhibition and web display purposes. Excellent.
I've also discovered a significant bug in the software. The first step after importing an image is to click the four corners of the region you want cropped and straightened. Prizmo excels at this operation but for one occasional crucial bug: the processed image sometimes has it's left and bottom edges cut off. At other times it's one of the other corners. This means I must manually adjust three of the four corners to compensate, introducing much trial and error and reducing the effectiveness of the radial distortion controls. When it behaves like this it's frustrating and makes Prizmo a one-trick Pony that doesn't do its trick very well-and it's a fairly expensive pony at that. When it works as it should it's a dream.
There are a few rough edges in the software that really should have been caught before release. The most embarrassing one is in the “image” slip that allows adjustment of brightness and contrast, etc.. There are three checkboxes, “Binarize”, “Invert” and “Homogenize”. Hover the mouse over any of them reveals a “tool tip” stating:
“Convert the image to black and white (dual tone without gray shades), potentially increasing outline accuracy”
It seems to me that this is a simple duplication of the tip for “Binarize”. There is no unique tip for Invert, which doesn't need one, and Homogenize, which desperately does. The manual states that homogenize is there to “smooth the output image luminosity”, which is a great feature for smoothing out uneven illumination on the original image though in practice it's a bit fiddly to get right. You need to play with the brightness and contract sliders to get a reasonable image with Homogenize activated. It also seems to make the image quite noisy.
On the topic of sliders they aren't large, which means you can see your image while working with them, but that makes them difficult to use accurately. Prizmo should take a tip from applications like Apple's Apeture (but not iPhoto) that allow multiple interactions with sliders: clicking and dragging on the slider for gross adjustment, clicking on arrows for fine adjustment, and direct display and editing of numerical values. Once you have the values the way you want them Prizmo will let you save them as a preset, which is very useful.
Image sizing and proportions can be quite hit and miss. Prizmo does a great job of guessing proportions most of the time and toggling the state of the “Automatic Sizing” checkbox seems to do the job. There are some custom size presets that are potentially very useful however the metric paper size presets, A5, A4 and A3, and perhaps the others for that matter (I never use them), clearly expect the image to be a portrait format document. Using them distorts any landscape images into portrait formats. There is not way of saving size presets so I can't even manually enter the sizes for portrait A4, A3 and A2 the way I'd like to. This is something that needs fixing.
When you're working on a whole batch of images Prizmo lacks an obvious way of working on a new image. The easiest way is to just drag and drop one onto the work area using Finder but this inherits the settings from the previous image. Using the File > Open Image… command produces the same result. There is no large dropzone like the one you get when you first launch the application.
Finally, when working on an image you'll probably want to see the preview larger to check your progress. There's a small disclosure triangle in the bottom left that does this but you can't zoom in on the preview and it doesn't fill the window. Inexplicably the preview corners are rounded although not the exported image thankfully. It would be useful to be able to view a larger preview image side-by-side with the original while you're working.
Overall I'm glad I bought a license for Prizmo. I did this despite knowing that it's not quite complete and is quite overpriced compared to most Mac software because I'd like to see it improve and the developers have already shown themselves to be responsive. I'll be watching this space.