Jump to content
The Beckham Digital Forum
Barry

DPI image size

Recommended Posts

I was about to sit down and record an update to some videos I created for my own club a few years ago on how to resize images for competitions.

Then I thought, in this day and age, why are we still doing this, especially for remotely judged competitions where even a 20MP image will save as a jpg between 1 or 2 meg. I can come up with a few reasons why some may not like the idea of submitting full size images, but I would like the views of other apart from me

1. Members worried about copyright, their images being stolen

2. That old chestnut that images must match the projector resolution. 

3. I will mention slow internet access here, but I don’t believe it’s a valid response

I would appreciate other views

Share this post


Link to post
Share on other sites

Definitely number 2.

It is also partly due to the organiser keeping images on their laptop for projection and trying to keep file sizes down to a minimum to save hard drive space. 

Now we have an upload area for competitions so each entrant can upload their images individually, ensuring they keep within the 1400 height/ width limit. We also upload images for projection during print competitions so all can see, again these going on the organisers laptop. It also allows auto comparison of images from each entrant to ensure they have not submitted a significantly similar image in another heat.

I would love to have a good explanation and evidence why we should not be keeping to the resolution of the projector 1400 x 1050.

Share this post


Link to post
Share on other sites

Also our club is sending images to Lincoln, Nebraska and Australia this month to be judged by these two clubs. Each entrant can submit 4 images, multiply that by a likely possible 30 authors and there will be 120 images to transmit. 

Share this post


Link to post
Share on other sites

Let me play devils advocate for a while.

It really cannot be anything to do with saving space on a laptop and it’s not a strong defence of the size practice given external drives, cloud  storage, disks etc.  I have never heard this once as a reason for the practice. Storage of images just isn’t an issue any more.

I don’t buy the resolution issue either. It seems to be thought by some that a projector cannot handle an image of higher resolution than its base size. In the days of 1024*768 projectors I constantly showed higher resolution images and never had any concerns over quality and I am a fussy bugger on that count. A simple test is to take half a dozen images to the club in high resolution and compare them with the same images reduced to 1400*1050.

I think this began in the days of dial up Internet as it did with an online group I was part of for years. 800*600 was the starting point for image size because each picture took an age to appear. Anyone recal watching the image start at the top and gradually appear line by line. The Internet has moved on and at this rate of size growth we will get to 4K size about the year 2100:)

Share this post


Link to post
Share on other sites

Fair point, I'll take some images and test out the higher resolution on the projector. They are probably storing the uploads on a server somewhere, if not then the Committee need to move into the present day.

Share this post


Link to post
Share on other sites

I have just set up something in PTE for our next meeting on the 12th Feb.

Viewing a 6000px image alongside a 1920px image on a 27in monitor, there is a little bit more sharpness in the lower res image as opposed to the high res, but whether that pans out the same on the big screen I am not sure. Out projector is a state of the art 1920*1080

The other thing to consider is higher res images may not show the halo we often see when editing sliders have been pushed and images reduced, so there may be a trade off there.

NB. In fact the resized images are all 1080 in height and around 1620 in width as you would expect from an SLR

Share this post


Link to post
Share on other sites
On 2/26/2018 at 6:10 AM, Barry said:

I was about to sit down and record an update to some videos I created for my own club a few years ago on how to resize images for competitions.

Then I thought, in this day and age, why are we still doing this, especially for remotely judged competitions where even a 20MP image will save as a jpg between 1 or 2 meg. I can come up with a few reasons why some may not like the idea of submitting full size images, but I would like the views of other apart from me

1. Members worried about copyright, their images being stolen

2. That old chestnut that images must match the projector resolution. 

3. I will mention slow internet access here, but I don’t believe it’s a valid response

I would appreciate other views

Re item 2, as my club is VERY fussing about the image size matching the projector size, I rather assumed if the image size was larger it would not fit on the projector screen and only part of the image would show. I now assume I am wrong but can you confirm.

Mickp

Share this post


Link to post
Share on other sites

Mick

Yes you are wrong. For many years I demonstrated at clubs with projectors that were 1024*768px, which were the top resolution at the time. I often showed slideshows created at 1920*1080 and they played perfectly OK. I have also shown high resolution images on our clubs projector with no problem. You don't get any of the image cut off.

So, there really isn't any reason for clubs to get overly worried about image size, but my own experience tells me they still do. I am guessing most of those who quote these things are just passing on what they have been told and few have just taken a few minutes to try it. I even had a judge contact me when remotely judging our images to ask if he should reject one of the images that was a few pixels over our size at the time. So, lots of people are well wrapped up in this myth. Perhaps in the very early days some projectors did cut off part of the picture, but I have never experienced it

How hard can it be to do a simple trial, but as I said in another post on this forum. Here we have a major South East Queensland Salon of Excellence event and the largest image size is 1620 px on the width. 

I did a test today with three different images. I placed one at high resolution from a 20MP camera next to the same image downsized to a maximum height of 1080px. So, 6 images in total. On a 27in monitor the lower resolution image looks a little sharper, because the high resolution one obviously had so many pixels crammed into the monitor size. (none of my images are sharpened in processing or when reducing size)  The thing to say about this is that the test is extreme. 6000px as against 1620px and will they show the same thing on the big screen through a decent projector? I'll let you know about that after the 12th March.

A lot of club members, even ones you may consider reasonably skillful have problems with image size resolution. I know this after putting together 24 slide shows a year for our club for the past  9 years. Sometimes clubs complicate the rules by not making them clear enough, especially when they also add a limit on MB as well as a pixel value. In one extreme case and going back 4-5 years,  newer members of one club i visited thought their images HAD to be fully 1024*768, not that they could be any resolution up to those values.

 

 

Share this post


Link to post
Share on other sites

I have always had trouble understanding 'native resolution' with respect to a projector and came to the conclusion that it was the maximum resolution that the projector could display at.

Eg; a 1920x1080 native resolution meant that the projector itself did some downsizing of images with higher resolution.

Is that another bit of nonsense? 

Share this post


Link to post
Share on other sites

To be honest I am not sure and most of my knowledge comes from practical experience rather than an in depth technical knowledge. If it does downsize the images, which seems logical, it seems to cope well, but as I said above it’s been a while since I did this.

it will be interesting to see the results of my test through a recently purchased Epson HD projector

 

Share this post


Link to post
Share on other sites

Let's assume that your 1920x1080 Projector is connected to your PC/Laptop via a HDMI cable. This is no different to connecting your 1920x1080 Monitor to your PC.

If you look at your Control Panel Display settings you will see that while you can set a lower resolution than the Monitor/Projector's Maximum/Native resolution you cannot set a resolution which is higher than the Monitor/Projector's Maximum/Native Resolution.

You therefore cannot send an Image to the Monitor/Projector which is larger than 1920x1080 for it to downsize.

The downsizing is done by whichever program you are using to display your image i.e. Bridge, PTE, Windows etc. In other words you can give PTE a 6000 wide Image to use and depending on the Zoom Settings in O&A 6000 wide will be 100% of the Screen Size in Preview or in an EXE. It is Downsized (by PTE) to 1920 wide (in Cover Mode) or 1080 high (in Fit Mode) in a 16:9 1920x1080 Project.

If you subjected a 960x540 Image to the same routine then the Monitor/Projector would use 4 Pixels to display 1 Pixel in the original Image.

The Full Screen Image transmitted by your Graphics Card to your Monitor/Projector is then 1920x1080 for a 16:9 1920x1080 Project pixel for pixel.

The only quality comparisons that you are able to do is Bridge vs PTE vs Windows etc. for the same image.

DG

Share this post


Link to post
Share on other sites

<on>

I think I am raising my own confusion factor.

The thread title cites "DPI" or dots per inch as used when printing on a printer. But y' all already knew this.

I am pleased that the thread conversation discusses imaging dimensions as pixels. Or "Pixels per Inch".

When discussing an image terms of pixel dimensions we should also include at what "Resolution" value.
Most monitors have a native resolution of only 72 Pixels /Inch.  For high quality image not much sense of using a image that has 300 ppi resolution.
Not sure about other display like projectors, Television screens, notebook or cellphones.
Note to self: Projectors Resolution rated "Vertical 600" apparently means: The number of pixels in lines from top to bottom on a display screen. The more pixels, the sharper the images will be.  Also described as 720p or 720 lines progressively written to screen from top to bottom 1 line at a time (row 1,2,3,4 etc) as compared to 720i or interlaced written to the screen every other line (row 1,3,5 etc) top to bottom and interlaced T to B to fill in space between row at space 2, 4 etc.

For images example:

In Photoshop I am looking at Tab for Image Size:

Resolution 96 Pixels/Inch
800 Pixels Wide x 707 Pixels High
file size 1.62 mb 

When I alter this images Resolution:
selected are [x] Scale Styles [x] Constrain Proportions [x] Re-sample Image

Resolution 72 Pixels/Inch
600 px wide x 530 px   Now smaller pixel dimensions
file size 931.6 kb  Now smaller file

</off>

Share this post


Link to post
Share on other sites

I think the thread title is referring to DPI as meaning Digital Projected Image, 360Texas. 

In our club it causes much confusion as we change this same acronym to PDI for Projected Digital Image in an attempt to get away from DPI also meaning dots per inch.

In your comments above I suggest that you can also untick re-sample image and change the resolution to 72 but keep the file size at 800 pixels wide x 707 pixels high keeping your 1.62 mb file. Interestingly by unticking the re-sample image the option to show image size in pixels is greyed out. 

Thanks also daveg for throwing some light on what is actually going on. If it is the software doing the downsizing then can there also be differences in images depending on the particular software doing the downsize?

 

Share this post


Link to post
Share on other sites

Dave

Let's assume that your 1920x1080 Projector is connected to your PC/Laptop via a HDMI cable. This is no different to connecting your 1920x1080 Monitor to your PC

I am not so sure about this in all cases because the projector we use seems to be very forgiving with noise in the images. I have always assumed that is is because these projectors are often designed for home cinemas perhaps, but I am only guessing.  It's not unusual to mention an image is a little noisy (easy to see on the monitor) but when you see the image on the big screen on club, the noise seems to be smoothed out. 

Share this post


Link to post
Share on other sites

I only concerned myself with resolution issues and for those purposes there is no difference between a projector and a monitor when connected by the same method - hdmi.

The projector might have various presets with regard to the rendition but that has nothing to do with resolution. When dealing with noise the normal methods add some sort of "blurring" or "smoothing". What feature (or problem) could the projector have which mimics that?

The only time that a projector would downsize an image would be when its media player is reading that "oversized" image from a usb source.

I am interested in how this one is resolved.

DG

p.s. what is being used to "deliver" the images - PTE, Bridge, Windows or something similar?

Share this post


Link to post
Share on other sites

The projector is working on default as far as I am aware and I don't even know if there are any global presents. Trouble is on club night there is never enough time to try these things.

p.s. what is being used to "deliver" the images - PTE, Bridge, Windows or something similar?

That's an interesting question because when the images are being viewed on club night they are within a fully created AV made with PTE. However, the judging of the images has already taken place and done remotely, long before the images find their way into a slide show. We have no way of knowing what the judge may use to make their judgement.

I will run a short test at the camera club on the 12th and see what the views of club members is. Thinking about what I can see on a 27in monitor, that  high res images look a little less sharp that a pre-sized one. I should see the same thing on the big screen, right?

 

Share this post


Link to post
Share on other sites

Just to clarify, what you are saying is that a full size jpeg viewed in (and resized by) PTE looks less sharp than its equivalent which has been resized to 1080 high in Photoshop?

Unless I am missing something what you are saying is that PS does a better job of resizing than PTE?

The sharpening setting in PTE would be the same for both?

That does not surprise me.

You SHOULD see the same on the projector but if you do not then you need to look elsewhere. You are NOT sending high res images to the projector. You are sending 1920x1080 data which has already been resized by PTE.

Could post an example where you see this?

 

Share this post


Link to post
Share on other sites

I think that the effect you describe can be seen in PTE.

I saved a 6000x4000 image (full res) and then resized it in PS (BiCubic Smooth Gradients) to 1620x1080. I used Save for the Web in both cases set at quality 60.

If you put the resized image over the unsized image in O&A and toggle the top one on and off there is a definite difference in quality in favour of the resized image.

I can post the images but it would be better if you try the same thing and either confirm or otherwise?

DG

Share this post


Link to post
Share on other sites

So, based on that, what conclusion do you come to?

Resizing, without adding sharpening, seems to give an effect similar to sharpening.

At this stage you could argue that using 1080 high images gives the best result for static images. Or, that if you need to use larger res images, they need to be sharpened. Have I missed something?

DG

 

Share this post


Link to post
Share on other sites

No, you haven’t missed anything, but my original question about image size is why we restrict images to be quite so small. Why would an organiser of an even restrict height to 1080 and width to 1620, which suggests it’s a 192O*1080 projector being used. Why not a full HD size of 1920*1080 at least. 

It seems organisers are locked into a 3:2 aspect ratio forgetting that if you add another 300px to the width it can be far more pleasing a shape and size for many of the subjects we display. Maybe it’s the same innexperience that restricts the AV section to files no larger than 31mb. I know some PTE experts who would struggle with that size and why 31?

That sort of drifted us into the debate on image size and how images would be seen on screen. In my experience I was using images of 1920*1080 on a projecto running 1024*768 so the difference between the two wasn’t so wide as we are debating here. In that case the visual differences cannot be seen.

I suppose it all depends on the goals of the competition. If it’s a straight past the post as in a club battle and a critique is not required, you could argue that higher resolution may put you at a disadvanatage.

If the aim is for a genuine critique of individual images, then as a judge I would like to be able to view an image slightly larger at times. I see that as no different to the judge walking closer to the print box when they suspect there is a quality issue and they are looking for confirmation to be able to suggest remedies.  Rather than guessing and being wrong 50% of the time.

The other issue about image size is how it confuses some newer members and some old ones too. Perhaps my projector test should compare images of 6000px and 1620, but also 4000px. Perhaps there is a sweet spot in there that isn’t quite so small.

When you take a club like ours where all competitions are remotely judged, it can be argued that any size could be submitted and perhaps the original image created from the camera would help the judge give constructive feedback. It just seems a little odd to me that I am putting smaller images into a competition now than I was back on 1972.

 

Share this post


Link to post
Share on other sites
On ‎27‎/‎02‎/‎2018 at 12:01 AM, Barry said:

Viewing a 6000px image alongside a 1920px image on a 27in monitor, there is a little bit more sharpness in the lower res image as opposed to the high res, but whether that pans out the same on the big screen I am not sure. Out projector is a state of the art 1920*1080

Subject to the audience's eyesight and viewing distance (and depending on the image) I can certainly demonstrate a difference in quality (and have done) between real time scaling (by a variety of tools) of images, on their way to the projector, and those resized and saved at the projector's native resolution, prior to display, using the most appropriate combination of algorithm and (if necessary) separate post resize sharpening.

This is not limited to differences in sharpness and loss of specific details but can also manifest as a loss of subtle differential focus effects – something that can need addressing manually, whether resizing from print ready sized images to projector resolutions or leaving it to real time scaling, as you are (at some point) losing resolution whilst simultaneously increasing viewing distance, both working to make similarly sharp elements look equally sharp when in the original one may have been noticeably sharper than the other.

Share this post


Link to post
Share on other sites
On ‎26‎/‎02‎/‎2018 at 6:10 AM, Barry said:

I can come up with a few reasons why some may not like the idea of submitting full size images, but I would like the views of other apart from me

1. Members worried about copyright, their images being stolen

2. That old chestnut that images must match the projector resolution. 

3. I will mention slow internet access here, but I don’t believe it’s a valid response

I would appreciate other views

  1. ... [modern upsizing algorithms make this laughable, and how big an ego do you need to think anyone wants to steel your images?]
  2. ... [actually, native resolution is the sweet spot you should avoid ignoring for ANY display; try changing the resolution on your 27in monitor for a few weeks and see how long it takes you to get a headache! Unless the image being real-time scaled was an exact multiple of the native dimensions you need to subsample across pixel boundaries and lose quality – even more than you would resizing with decent algorithms with the same mismatched dimensions.]
  3. ... [try being the one to have to download a few thousand images for an exhibition, let alone being able to process and review them]
  4. For collation of pictures for current (or future) competitions matching size restrictions imposed by other bodies (without organisers having to return to the authors or resize on their behalf).
  5. Complete control over resizing algorithms, including control over the degree (and location) of any sharpening.

Share this post


Link to post
Share on other sites
On ‎27‎/‎02‎/‎2018 at 8:28 PM, 360texas said:

Most monitors have a native resolution of only 72 Pixels /Inch. 

I won't confuse things by going into the concept of reference pixels here but you are (generally) better of leaning towards 96ppi not 72ppi as your go to screen standard nowadays.

On ‎27‎/‎02‎/‎2018 at 11:55 PM, Tinion 45 said:

Interestingly by unticking the re-sample image the option to show image size in pixels is greyed out. 

That's because the only option then is to change how those pixels are spread over physical dimensions.

On ‎27‎/‎02‎/‎2018 at 11:55 PM, Tinion 45 said:

If it is the software doing the downsizing then can there also be differences in images depending on the particular software doing the downsize?

Absolutely and also between the results of using different options offered by one piece of software.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

×