June 6th 2015 – Note, I am in the process of updating this analysis with new photos. The results are not dramatically different but I was able to improve the horizontal resolution slightly and now have some better pictures.
One of the first things I noticed when projecting text pattern images with the Celluon PicoPro was that the images were very blurry. I later found out that the smaller the image the blurrier it became.
To the left are high-resolution center crops of images taken with a 12-inch diagonal (about as big as you can get on a letter size sheet of paper, a 24-inch diagonal image (about as big as fits on a standard “B” size sheet of paper, and a 72-inch diagonal image I project on a wall. For reference I have also included a the same portion of the source 3x magnified.
As you should notice the 12-in diagonal image is completely blurry even at 1/2 the stated resolution. With the 24-inch diagonal you can start to see some “modulation” of the single pixel size lines horizontally but not vertically. With the 72-inch diagonal the horizontal lines are pretty clear but still the vertical lines are still pretty much a blur (on close visual inspection there is a little modulation of the single pixel wide lines).
What is happening is that size of the laser beams is larger than the pixel size for small images. The size of the beam diverges but at a slower rate than the size of the image grows so eventually the laser beam size is smaller than a “pixel” and you start to see separation between horizontal 1 pixel wide lines.
As for the horizontal resolution, whatever is driving the lasers in their horizontal sweep is not able to fully modulate them at single pixel resolution.
For the next set of 3 images (plus a 2x Magnified source) I have scale the images down so you can see more area. Note you need to click on the image to see it at its intended size and to see the detail. In these pictures you can see the ruler with both indicates the size of the image and shows that the camera was in-focus and could see the detail if it was in the projected image.
On the 24-inch diagonal and 72-in diagonal image I have drawn 3 ovals. The left oval is around a set of 4 line pairs (see source image) of horizontal and vertical lines. The middle and right ovals are each around 4 line pairs of vertical lines and two sets of 4 pairs of horizontal lines and where the horizontal and vertical lines cross is a set of 9 white pixels (never visible in any of the projected images).
Looking at the 72-inch image you may notice that you can barely make out the horizontal line pairs in the center oval but that they become blurry in the right oval. This is due to the interlaced Lissajous scanning being done (for more detail on the Microvision interlaced scanning process see: https://www.kguttag.com/2012/01/09/cynics-guild-to-ces-measuring-resolution/). The net effect of this scanning process is that vertical resolution is reduce from the center to the left and right sides.
The 5 year old Microvision ShowWX having this blurring issue with small images. In looking inside at the optics with the lasers on, I notice that the laser spot sizes were larger than expected. I’m left wondering if the larger laser spot sizes were at least in part cause by efforts to reduce speckle or for some other reason.
Next time, I plan on giving a little “tour” of the optics.
Addendum – How the pictures were taken, full resolution images, and source pattern used
All the pictures were taken with a Canon 70D (5472 by 3648 pixel) DSLR. By framing the pictures so that filled roughly 90% of the width, this meant there were roughly 4 camera pixel “samples” per pixel in the output image. The ruler in the picture was both to keep track of the size of the image and to make sure the camera was in-focus and could resolve single pixels (if they were there).
I did selectively zoom in with the camera on smaller regions to see if it made any measurable difference in resolving features in the images and it did not. I have included the test pattern I used and would welcome anyone using it to verify what I have shown.
By clicking on the thumbnails below you will bring up the full size image (depending on your browser it may not display full size until after you click on the magnifying glass). You can then right click to download the images. Each image is about 8 to 9 Megabytes and is stored in a high quality (low compression) JPG format. The source test pattern is stored in loss-less PNG.