DIY Resolution Target

February 2, 2010

I know you’re all pacing a groove in the carpet, waiting for hot news about this month’s upcoming micro Four Thirds cameras. I am too.

But to give you something to occupy yourself in the meantime, here’s a handy little test target. It’s useful for checking how closely a camera’s resolution approaches the spacing of its sensor pixels:

Resolution Limit Target

Test Target for Resolution Limit

Download the PDF file here, and print it out at full size. It’s a 600 ppi bitmap, and each tile should measure one inch square.

The numbers give the divisions per inch—that includes both the black and white stripes.

Now, photographed at a certain magnification, one spacing of stripes will exactly match the pixel pitch of the camera. Ideally then, zooming all the way into the image should show one row of black pixels, then a row of white pixels, etc.

Let’s say you have an 8 megapixel camera, which creates 3280 x 2460 pixel images. To match up the 40-lines/inch sample to your pixel spacing, divide 3280 by 40; you get 82 inches.

On a nearby wall, put up two marks 82″ apart (using tape, post-its, etc.). Set up the camera and zoom/move until the picture width exactly matches the marks. (Note that many viewfinders show slightly less than the true image size).

Tape up the test target near the center of the frame, where lens aberrations ought to be lowest. The setup looks something like this:

Resolution Test Setup

Field of Measured Width, Target

To make your test more reliable, be sure to:

  • use the highest JPEG quality setting
  • put the camera on a tripod
  • repeat the shot a few times, and select the sharpest
  • use the lowest available ISO setting
  • check that other settings (sharpening, etc.) are typical of your use

When you take a magnified look at the resulting image, you may see something resembling this:

Resolution Check Results

200% View of Resolution-Check Image

The 30-line sample looks a little lumpy; but it is actually resolved (you can count the correct number of lines). Not too surprisingly, the 50-line sample is not resolved—although you do get a hint of the line orientations.

But most interesting is the 40-line sample. Ideally, you’d see black & white lines exactly matching the pixel spacing. But because of the Bayer demosaicing, some decidedly funky things have happened. (Read a good explanation here about how demosaicing works.)

The target lines aren’t resolved—and they’ve actually created some false colors and textures.

Now, more natural, irregular subjects won’t show such alarming artifacts as this. And notice that the hairline around the number squares remains faintly visible, even though it’s much narrower than one pixel.

But down at the individual-pixel level, sensor resolution can become a bit shaky. Check for yourself and you might be surprised.

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14 Responses to “DIY Resolution Target”


  1. So, how would this exact same shot look if you had used film? I don’t own a film camera anymore and therefore, cannot try the test myself. Have you performed this test with film? If so, I’d love to see the results.

    • petavoxel Says:

      A fair question, but which I haven’t checked. I’d expect the film resolution to degrade more gradually down to the point where grain dominates.

      • petavoxel Says:

        A footnote: I did test recently and found that 35mm Provia slide film did not resolve as well as a 12 Mp DSLR (and interestingly, also showed some false purplish color in the finest lines); while 6×4.5 Pan F (fine-grained B&W film) definitely outresolved the DSLR.

        Both film cameras were using known-excellent lenses at optimum f/stops, to make it a purer test of the media resolution.


  2. […] had a chance to take some sample shots with the 8-megapixel Nikon Coolpix P60, using the resolution test target I posted last week. (Open a tab to remind yourself how the target is supposed to […]

  3. Patrick Says:

    Interesting challenge. I took out my 3 cameras for a comparison — since there isn’t anything better to do while shut in by snow — a 3 mp Panasonic FZ-3, a 10 mp Panasonice FZ-28, and a 12 mp Canon XSi.

    If I got everything correct, I found that at a pixel-level (viewing at 100 or 200%), the FZ-3 was the only one where I could see individual lines at the 40 or 50 lines per inch. The 40/in. came out as a checkerboard, and the 50/in. showed lines, even if a bit blurred and some color effects. At this level of viewing there were a lot of the usual flecks/noise/etc.

    The FZ-28 was a bit dodgy at 30/in. (about as good as the FZ-3 at 50/in.), and 40 & 50 were gray blurs. Similar level of flecks/noise.

    The Canon XSi was smooth as silk, no noise, but surprisingly the 40 & 50/in. squares were also gray blurs.

    Question: Does it matter if my tripod was not quite level?

    • petavoxel Says:

      A tilt to the tripod will make any demosaicing artifacts take on a different look—although it ought not change the overall point where resolution is lost.

      One difference of a DLSR is that it will definitely have an antialiasing filter over the sensor. This is essentially “frosted glass” which is there to prevent moire when fine lines are closer together than the pixel spacing. In compact cameras there is usually not enough lens resolution to worry about this! Although it sounds like your FZ-3 “checkerboard” was a case where the lens resolved enough detail to make demosaicing spazz out.

      Just so I’m clear—you did change the field width to reflect to the different pixel pitches of each camera? (That is, to match the FZ-3’s pixel pitch to the 40 div/in squares, divide 2016 pixels wide by 40 = a 50.4″ wide target field.)

      • Patrick Says:

        Yes, I had 51″ for the FZ-3, 91″ for the FZ-28, and 107″ for the XSi.

        The XSi was the kit lens, i.e., 18-55 IS.

      • petavoxel Says:

        Excellent.

        As I mentioned in my last post, texture in the 50-line squares is likely to be aliasing (rather than accurate resolution). But it is a sign that the lens is still resolving detail at that level. So the lens of the FZ-3 was apparently out-performing the sensor. (DP Review really liked that model.)

      • Patrick Says:

        If it weren’t for the poor ISO 400 performance and the tiny (1.5″) LCD — near impossible to check focus unless you zoom each shot — I didn’t need to get the FZ-28. Even at 3 mp I’ve printed a few 8x10s that look good unless you hold them at less than arm’s length.

  4. alex-virt Says:

    Here is the result of my test with the Sigma SD14 and two lenses: 28/1.8 prime and 17-70/2.8-4.5 zoom. I’ve chosen the best three pictures from diffrent focal lengths and apertures. Sigma does resolve 40 lpi, and all imperfections are due to improper vertical alignment of the camera and test chart.

    200% magnification here: http://farm5.static.flickr.com/4062/4363141439_87098c05d1_o.jpg


  5. […] week I made a post about lens sharpness, referring to MTF graphs. While the little test target I posted on this blog has solid black & white bars (which was easiest for me to create), formal […]


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