Harris Kalinka

Imagery + Animation Golf + Architecture

Wednesday 4th March 2015

Displaying your rendered images: what does resolution matter?

In January’s post ‘Printing images: what resolution do you need?‘ I tried to clear up a few common misconceptions when it comes to image size and the resolution of digital images when you print them, and what we need to know to render your images at the correct size.

This week I’m looking at images that are displayed digitally. What resolution image do you need? And does the resolution of the image even matter at all?

The good thing with images that are displayed digitally is that you don’t have to worry about ppi (pixels per inch) or dpi (dots per inch) when it comes to image quality. In fact, when it comes to displaying your images on any digital device, the resolution of your image is irrelevant. There is only one thing that counts: image size, that is the total number of pixels in the image.

That is to say, if you have two images that are 800 x 600px (where ‘px’ is pixels), but one has its resolution set at 72ppi and the other has its resolution set 300ppi (or even 3,000ppi), then they will appear exactly the same size when shown on screen.

Architectural visualisation with a resolution of 72ppi

This visualisation has been rendered at an image size of 3200 x 1828 pixels. The resolution is 72ppi but this has no effect on the the size it appears on screen.

Architectural visualisation with a resolution of 300ppi

This visualisation has been rendered at an image size of 3200 x 1828 pixels. The resolution is 300ppi but this has no effect on the the size it appears on screen.

So we can say that a digital image doesn’t have a resolution. A digital image only has pixels, and this is all a computer screen cares about. How big that image appears on a screen depends on the pixel dimensions of the image and the display resolution of the screen.

If an image is 800 x 600px then it will appear at 800 x 600px on every computer. Of course they may look “bigger” or “smaller” on different computer screens, but this is because not all monitors have the same resolution (they don’t display the same number of pixels per inch). Most screens have a resolution in the range of 67ppi to 130ppi.

Images for websites and apps

For those of you who often save images at 72ppi for websites, you might be surprised to find out that the resolution has no impact on the file size either, so your website will load just as fast if the images were all 300ppi. What does affect the file size is the number of pixels and the image compression.

‘Compressing’ images

Image compression is all about reducing the file size of a digital image rather than reducing the size at which it is displayed. It’s most important for images that are intended for use on a website, because the smaller the file size the quicker the image, and the website, will load. However, it’s important to find a balance, because the more the image is compressed the lower the quality will be. Compression is inherently linked to the file types such as JPEG, TIFF, GIF, PNGs – image formats used on websites. Image software, such as Photoshop, offer various ways to you can compress image files.

If you need to reduce the file size of the image then an alternative to using image compression is to reduce the size the image will appear on the screen, this means reducing the number of pixels in the image, for example changing an image that is 800 x 600px to 400 x 300px.

Images for presentations

When you present your images using a projector, there is no difference in what you need. We will render images in exactly the same way we would if you were to use them for a standard computer screen. The resolution of the image is irrelevant – all that is important is what it looks like on the computer screen.

In fact it is not possible to project an image at a higher resolution than it is shown on the computer screen because it is simply replicating what is already there. If it looks good on the screen then it will look good when it is projected.

Of course the image will appear bigger, but we also have to consider that the viewers are probably viewing the projection at a greater distance.

I hope these last two posts have helped you to understand some of the confusion that surrounds the size, resolution and output of digital images. It might seem confusing, but as long as you can tell us what you need the image for we’ll make sure you have it in a format and size that always gives you the highest quality images of your projects and designs.

In a future post I’ll discuss some of the subjects that are more relevant to those who work in the visualisation industry, such as the different types of work flow, colour space and monitor calibration.