How To Get The Sharpest Image From Your Display

This article is about how to obtain the sharpest image from any given display.  The final goal is to not lose any image details from the source while not adding anything that is not in the image.  In many products achieving both of these goals may not be possible.  When that is the case you need to be aware of the trade offs that you are making.

The first thing to review is if you are close enough to the display to see the image as sharp as it can be presented.  This calculator will help you determine if you are close enough for your product and the source in question.

On a front projector you need to remove any keystone correction added to the projector if possible.  This adjustment  is meant to correct for improper projector mounting.  You should not use this if you want the sharpest image possible.  It is better to use lens shift and alter the projector height or orientation to the screen to have an image with good geometry.  In fact it is generally better to accept a subtle geometric error than to soften the image or create moire with keystone correction.

Many parameters of projector performance will change the apparent image sharpness.  The more you stop the lens down with an iris in the lens the sharper the image will be.  The higher the ANSI contrast the sharper the image will be when things are bright, but this can be reduced by reducing iris aperture.  A dark room and dark furnishings will improve ANSI contrast.  The higher on/off contrast is the sharper the image will be when it is darker.  The further the projector is mounted from the screen the sharper the image because less of the lens is used to project the image.  Using more lens shift to mount the projector from the ceiling can reduce image sharpness by using less accurate regions of the lens, but it may also increase ANSI contrast which will improve apparent sharpness in bright images.  Using an Anamorphic lens will reduce image sharpness.  Adjusting these things to improve sharpness can be problematic while attempting to achieve a target light level and desirable projector location, but they are important factors to consider.   The degree to which image sharpness varies from these factors varies by product sample and type.

Clean optics are important for front or rear projector sharpness.  Be sure you do not have smudges or a film on the lens and clean it carefully if necessary using lens cleaning methods like those for photographic lenses.  When using cleaning solution always make sure you do not use so much that it gets inside the lens.  Use as little force as possible when doing this to avoid damaging the lens or coatings on the lens.

Any display will not look as sharp as possible if the gamma and the light output are not close to optimum for the display in question.  Simple procedures for adjusting contrast, brightness and gamma are available on products like Digital Video Essentials, but they may not produce the best results possible without test equipment or knowledge about display peculiarities in these areas.

Next you need to make sure all of your sources are getting to the display at the maximum resolution possible.  You can check this by playing a high quality source on your Blu-Ray player or other HD source and reviewing that the display is receiving this at the proper resolution which is usually 1080i or 1080p.  If this is not the case you need to change a display setting in a video processor in your receiver or other device or the source itself.  Digital connections like HDMI and DVI should generally be used to obtain the sharpest image possible.

Geometry needs to be correct to do these tests.  Be sure that a circle looks like a circle with a known test pattern.  Changing the aspect ratio correction on the screen will correct for these errors.  The Spears and Munsil test disc is a good place to find this.

Focus and convergence are the next things to adjust on a front or rear projection display.  Panel alignment only exists on some three chip projectors like DLP, SXRD and D-ILA products.  Adjusting panel alignment and focus is an interactive process.  Start with focus and then go to panel alignment and repeat until it is as sharp as possible.  I look at the pixel grid pattern along with text to judge focus.  In a well focused system the pixel grid and text should be well defined.  Try rocking the focus back and forth around good focus to find the point that is the sharpest in the center of the image.  For panel alignment I like to use a black line pattern on a gray background like that on the AccuPel test generators.  The Spears and Munsil test disc is a good place to find this.  Be sure the test pattern you are using matches the native resolution of your display (720p, 1080p…) to ensure you are not causing other errors.  Also get very close to the screen so you can see these things easily.  Sony has a test pattern on their Blu-Rays that can be accessed to check resolution by typing 7669 from the main menu.  This will not work on some players.

The next thing to check is to see if the display is pixel mapping the image.  To do this you need to use a single line pixel burst which consists of alternating black and white lines of 1 pixel width.  The Spears and Munsil test disc is a good place to find this.  These should be represented cleanly and not with a different frequency than the pixel grid itself.  If a lower resolution or variable resolution is displayed you need to find the control that sets the overscan in the product or remove an anti-alias filter to restore the display resolution. These have various names and can be difficult to locate.  But when things are correct the 2 pixel width pattern should look very similar to the 1 pixel width burst except for the line width.  Once this is complete go back and repeat the panel alignment and focus on a front projector if you had to change anything.

The next thing to check is the sharpness and detail enhancement controls.  I find the best way to do this is with black horizontal and vertical lines on a gray background of 1 to 5 pixel width like that on the AccuPel video generator.  The next best tool is the Spears and Munsil test disc.  A sharp image will transition cleanly from gray to black with no white lines around the black line.  The maximum sharpness will occur when the black horizontal and vertical lines are as dark as possible.  Be sure to pay very close attention to this.  If it is necessary to have a little enhancement around the black line to achieve this it is probably a good trade off.  This will maximize image MTF which is how we see sharpness.  It is likely you will need to locate multiple controls that control image sharpness such as sharpness, detail enhancement and anti alias filters to get the best performance possible.  The labels for these controls will vary by product.  Be sure to revisit focus and panel alignment after this step and recheck sharpness and image enhancement if those change.

When you are done a perfect display will show the 1 pixel width burst to be as bright as the 2 pixel burst with the black lines being very dark between the white lines.  Examples of these test patterns are shown below.

Hopefully, this will help you obtain the sharpest image possible from your display while adding as few artifacts as possible to the images you are watching.

W. Jeff Meier

ISF and THX Certified Home Theater Consultant

1 Comment
Kenobi

Thanks much for sharing. This is invaluable advice.

Best regards,

Kenobi

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