What is the Keystone Correction of a Projector?

octobre 07, 2020

What is the Keystone Correction of a Projector?

What is Keystone Correction?

If you own a projector in your home or at your office then the term keystone is not something you are unaware of. When a projector is not perpendicular to the screen or the projector screen is angled in such a way that it leads to misalignment, it gives an effect called the keystone effect. But don’t worry! It’s not something that you can’t solve.

The keystone correction is a handy feature for those who own projectors and other electronic devices. There are many layers to it but the salient feature is the angle of keystone correction. The following is an example of what the keystone effect may look like.

The keystone effect can be fixed by two means; manual and digital. The manual correction method requires the adjustment of the projector and the room to accommodate keystone correction. This endeavor requires the lens projector to be adjusted in either a higher or lower angle with regards to a flat surface. On the other hand, digital correction digitally converts the data and scales to correct the keystone effect.

The manual method was used by old projectors. Nowadays, digital keystone correction is already embedded in a projector, hence automating it and making it easier to correct. It has opened a door to numerous possibilities in projector placement.

Even though keystone correction is an essential feature of a projector, it has both a good and a bad side to it.


  • Adjustment of displayed data on the screen
  • Reduction of distortion
  • Adjustment of project image regardless of distance


  • Reduces the resolution of displayed data
  • Not a permanent solution
  • Effects the overall quality of images

Angle of Correction

Since almost everyone owning a projector deals with the keystone effect, people often have questions regarding the correct angle of corrections to adjust their images. But there is no definite answer to that. The angle of keystone correction varies from ±30° to ±50° but the distance of the projector, the screen and the model in use should be taken into account.

When a projector is set on a plain surface the angle isn’t taken into account, but if mounted on a standard lamp it gives an angle up to ±100° vertically and an adjustment of within ±5° horizontally. Moreover, if mounted on a portrait lamp it gives an adjustment angle up to ±10° vertically and ±10° horizontally.

The angel for keystone correction has been mentioned above and as it stands, it varies. It depends on the model of the projector being used and the degree of vertical or horizontal correction that is required. Now there are different ranges of projectors whose angle of keystone correction is different from the other, the reason being that every projector is equipped with different specifications that react differently to the keystone effect.

To talk strictly in terms of the angle of the correction for all the different projectors is impossible, and rightfully so. As this suggests, it is important that before you purchase a projector, you should become familiar with the angle of correction that the model offers for the keystone effect.

We understand that it’s not always convenient to place your projector in the center of the room, and a distorted image is an annoyance. You may have to carry a portable projector, which makes the keystone effect even bigger trouble for you. The keystone correction is your best solution to fix a trapezoid-like image and so you must take the angle of correction in consideration before buying a model of projector, as it fulfills your need for image adjustment completely.

How to Adjust the Angle Properly?

When you explain the cons of buying a projector and present solutions to fix the deformed image, it seems like a hard job. Although digital angle correction has made it way easier today, keystone angle correction still sounds like a scary hassle to many people.

It might seem like an added hindrance in the beginning, but it’s something that you’ll get used to very easily and once you do so, it’ll become an added convenience for your projectors.

To help you get through the process beforehand, we listed some steps for you to make adjustments to your image:

  1. Display your image – obviously, the first step is to check if your image needs angle correction or not. You might have placed the projector at the right-center from the very beginning, eliminating the issue of keystone effect anyway. But this is rare and is usually only possible in proper offices or auditoriums etc. If you’re placing one at your home, there might definitely be some sort of deformation of the image being displayed.
  2. Adjust the place of your projector – although the whole purpose of keystone angle correction is to remove the manual labor involved in the correct placement of projectors, it’s always better to place it at the most convenient center. This is because the lesser the image distortion, the lesser will be the image degradation after necessary angle corrections.
  3. Distort the image yourself – Keystone angle correction is a form of image distortion that changes the angles of the output image to make it rectangular to the audience. This can be done by using the buttons present on your projector. As the models differ, so do the functions, button positions, button labels, etc. But almost all projectors in the market today offer angle distortions for both vertical and horizontal directions. Whether your image is too high or too low, or even expanded on one side or the other, the buttons will show you your way along with adjustments!
  4. Zoom in, or out – to fit your screen perfectly, you might need to zoom in or zoom out the output image too. Again, there are necessary buttons present on the projectors for that.

What’s more important is that for such digital controls, you can even make the slightest changes in front of you while observing the output image without worrying about moving the projector too much.

Is the Resultant Image Degradation Worth It?

You should be familiar with the fact that the keystone effect is fixed on the cost of image quality. The resolution drops with respect to the angle of correction because this is a digital process to fix the distorted image. On the contrary, manual adjustments of the projector don’t involve any sort of digital manipulations.

In fixing an image by stretching or shrinking it, or zooming it in or out, the pixels of the image will be directly affected. If there isn’t much difference you observe in the old distorted and the new perfectly shaped image, it’s great! But the resultant image is always less sharp than the original one. In some cases, the low resolution becomes so troublesome that it even sometimes ends up in mathematical errors, giving you a completely ruined and degraded image.

However, what still makes the keystone angle correction a great added adaptability to the use of projectors is that it’s a one-click change. It doesn’t cost your ease and can easily be fixed sitting on your couch, there is no physical labor involved.

Now if you think about it this way, that the manual adjustments of the projector aren’t always precise but the digital angle correction is an easy and accurate solution to your problem, then it seems like an idea totally worth it. Besides, if the audience is at a considerable distance from the screen, they might even totally be unaware of any quality distortions. Unless you’re really trying to pick the image quality, it won’t pose an issue.

Importance of Angle of Keystone Correction

It might not seem like it but the angle of keystone correction is really important in determining how your projector works and what quality of use it gives you. In terms of the angle of correction, the ideal angle is that of ±40° which allows balanced flexibility and maintains the dimensions of the image; let it be rectangular, square, or trapezoid. The higher the angle, the lower the flexibility, and the lower the angle, the higher the flexibility of the projected image.

The keystone effect tends to cause diminishment and ruins the image being presented. The angle correction helps the image being projected to restore balance in terms of translucency and light diffusion. It helps to hold up the quality of the image and allows the user to create a customized shape of the image being projected.


It’s fair to say that the importance of the angle of keystone correction cannot be overlooked. It’s extremely vital in determining the image quality, its dimensions, and its alignment. So, while you are in search for a projector for your house or your office apart from the major specifications, do ponder upon the angle of correction as well, otherwise, it will undermine your use of the projector and the projected images might not be what you would have hoped for.

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