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Reducing image resolution for projection

maroondah Plus
14 239 1 Australia
7 Oct 2011 1:23PM
Hi everyone,

Please forgive me in advance if this question has been asked before but I need an answer from someone who really knows. In our photo club we are asked to re size our images from its original size (in my case between 4 & 8 MB) to 1024 pixels or 768 pixels. The simple question is, does reducing it in size affect the image quality when projected. Thats all I want to know. Within the club the answer varies from person to person.

Any help would be most appreciated.


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PP Plus
16 222 England
7 Oct 2011 2:37PM
Resized images tend to lose a little sharpness compared to the original, so you may want to rectify this.

The main difference I notice is that projected images tend to look different colourwise, compared to the original, never been sure about the reason for this though.

User_Removed 8 4.6k 1 Scotland
7 Oct 2011 3:10PM

The main difference I notice is that projected images tend to look different colourwise, compared to the original, never been sure about the reason for this though.


Shouldn't if the projector has been properly calibrated.

This used to be a problem for camera clubs - members spent hours "perfecting" their image files for competitions and then they looked rubbish when projected on the club's projector.

But a modern projector, properly calibrated, (to take account of ambient light and screen surface amongst other factors) should be OK.

At the resolution you quote, the image should look just as good as it would on a computer monitor at the same resolution. You really only need 5Mb files for printing. On any computer monitor or digital projector, 1Mb is as much as you will ever need.

Maybe your club projector is a wee bit old. Ours projects at 1400x1050 pixels and, at that, 1Mb is still sufficient for the best image it can produce.

The other tip is to make sure that your computer monitor(s) are calibrated to the same (or equivalent I should say) profile as the projector, otherwise you will never get an image to look the same on the screen as on your computer.
MeanGreeny Plus
12 3.7k England
7 Oct 2011 3:13PM
Image quality really suffers with an old projector which has a resolution of 1024 x 768.

Prices of higher resolution projectors [1920 x 1080] have only recently become relatively affordable for camera clubs.
Dave_Canon Plus
11 1.3k United Kingdom
7 Oct 2011 3:31PM
Your question is does the reduced size affect the image quality but compared to what?. If you are asking whether a PDI will look as good quality as an A3 print then the answer is no it will not. Projection of images are still a difficult problem. My club is into its second projector because our original DLP (1024 by 768) even carefully calibrated could not produce good enough quality for competitions. DLP projectors typically use a white segment to boost the light output at the expense of shadow detail. If you reduce or turn off the white segment the light output may be too low for a hall. We now use Canon LCos technology and a 1400 by 1050 projector but this still has problems even though much better. Careful calibration is required but the highlights tend to be boosted thus spoiling high key images. We have made some manual light output adjustments to improve this but Canon do not seem to have a full solution to this. We have spoken to other Clubs who have the same problems. We can only hope that the next generation projectors will solve these problems.

User_Removed 14 3.3k 4 United Kingdom
7 Oct 2011 4:32PM

Quote:does reducing it in size affect the image quality when projected. Thats all I want to know

No - if the resolution of your club's projector is only 1024 x 768 and you provided a bigger file the display software or the projector itself would still have to reduce the image in size (throw away surplus pixels). This it might do in a quick and dirty way on-the-fly.

Doing it yourself first in Photoshop gives you more control and Photoshop does a good job.
maroondah Plus
14 239 1 Australia
7 Oct 2011 4:43PM
Many thanks everyone. The points you raise really help me understand what we need to do.

Regards to you all
SueEley Plus
11 279 96 Wales
7 Oct 2011 6:44PM
I agree that a profiled projector is vital, but as you are quite possibly changing the colour profile of your image when you ready it for projection, you might get a colour shift from your ideal as a result of the smaller gamut, especially if you need to use sRGB? When you print, out of gamut colours might be rendered differently. But probably this is irrelevant and I am burbling...
maroondah Plus
14 239 1 Australia
7 Oct 2011 6:59PM
Hi Sue,
Not rambling at all. Any information given helps me understand why members in our club are confused.
Many thanks
Dave_Canon Plus
11 1.3k United Kingdom
9 Oct 2011 9:44PM
Your Club will probably wish to run Competition Software and there are several software packages available for Club, national and international competitions. As far as I am aware, the software available has been written by Club Photographers thus ideally suited for its purpose and is generally sold at a very good price and supported. The package we use is called PhotoComp and will automatically convert Adobe RGB to sRGB and also resize images to suit the projector. The normal convention is that oversized imaged are reduced to the projector size but undersized images (a mistake) are projected as supplied. It is best however, to resize using Photoshop, Lightroom, Elements etc. yourself.


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