Calne Camera Club

Detailed Explanation on the Whys and Wherefores of Submitting Images for Digital Projection
I realize that these instructions may seem a little long winded but I hope that by understanding exactly why you should resize your images in a certain way you will save time and effort when you next submit digital images for projection.

Size really does matter.
I have noticed a few members are having issues when they resize their images for submission electronically for projection at a meeting or for competition so I thought I'd write a few words about the process. To begin with lets consider the semantics of what we mean by file size because this is where the confusion lies as "size" in relation to image files can refer to two totally different things:
the physical, pixel dimensions of the image, and
the number of bytes a file takes up on a disk

Let us start with the physical dimensions of the image. We ask that when you submit your images for projection that you resize your image so that the width does not exceed 1400 pixels nor the height exceed 1050. Why 1400 pixels? Because that is the native resolution of the projector.
If your image is not resized to take advantage of this characteristic of the projector your images will not look their best. If your image is too small the projectionist has to decide if they should show your image small with a border around it or if they should stretch the image to fill the frame. If your image is too big the projectionist can shrink the image to the projector frame but if very much over size it will not look as good as had you submitted the image at the correct resolution to begin with.

Why is this?    If your image is too small and we are stretching it to fill the frame, the computer has to guess at what to add to the image to make the picture look bigger. If your image is too large, the computer has to decide which lines to discard to shrink the image. Neither of these processes is optimal for your image's fidelity.

So, how do you resize your image to send it to us?
First, make a copy of your image and work on that. Call it whatever you like but make and use a copy.
All the programs I have used (PhotoShop, PhotoShop Elements, Gimp, Paintshop) have similar interfaces for achieving this. The menu option you use will be something like Image > Resize > Image Size. The only thing you have to make sure of is that you are resizing the image itself and not the canvas upon which the image resides. Usually you will now see a dialogue window that shows the image's current dimensions and allows you to change these dimensions. The most important thing to remember is that the only thing that matters is pixels; forget about combinations of dimensions in inches and resolution in pixels per inch this is only important when you are printing your image. We just want to change the dimensions of our image for the projector (or screen) and these display devices don't know anything about inches they only understand pixels.

To resize your image you may have to check a box labelled "Resample Image" and chose a method to achieve this. I choose Bicubic which is generally accepted as the most accurate and convenient method in this situation. You must also check the "Constrain Proportions" or possibly "Maintain Aspect Ratio" option; this ensures that your ratio of image height to width is maintained as the image size changes.

Look at the current image size; unless your image is perfectly square one dimension will be larger than the other. For the moment forget the terms "Landscape" and "Portrait" simply be certain which is the width and which the height.

Change the width value to "1400 pixels" the height value should also change at this point if this value exceeds "1050 pixels" then change that back to 1050. The width value of "1400 pixels" will of course reduce at this point. That's ok leave it as it is, your ratio of image height to width (ie. the overall shape/proportion) is maintained.

Using this method you will ensure that your final image is neither too wide nor too high, yet you will have achieved maximum use of the available space. Unless you have cropped your picture to fit, it is unlikely you will meet both extremities. That doesn't matter just don't exceed them.

Incidentally this 1400 by 1050 maximum dimensions of the projected screen image is exactly the same ratio as required for images on these web pages. So images submitted for the club's web site can be sized in the same manner. Pictures shown here, no matter what their shape or size are show within the same ratio on an invisible screen.
Actually, depending on the speed of your browser, you may see a ghost of a black screen just as the page loads.

The next step is optional but I now look at my image at the "actual pixels" zoom level and apply the unsharp mask to an amount appropriate to the subject and the new image size. Sharpening is a subject for a larger article but, to keep a long story short, I sharpen to some extent as the final step before saving every time I resize an image either up or down.

You now want to save your resized image as a new file name (Save As); if you just do a blind save there is a danger that you might over write the original file which would be bad.

Some notes on Compression.
When you hit the save button, as you chose the jpeg file format, you will now be asked how much compression you wish to apply to the image.
If you are not asked directly, there will be an "Options" button, try that, ignore all options other than compression.
In Adobe products this is a scale from 1 to 12. Up to now we have been dealing with size as it relates to the physical dimensions of the image but compression relates to the byte size of the file. The more compression you apply to an image the smaller the file size you end up with however there is a cost; image fidelity. When compression is applied, image data that probably isn't important is discarded; the operative word here is 'probably'. Compression is a mathematical process; the more severe the compression you apply, the more data is discarded and the smaller the resulting file size. When you are sending images to friends and family and you don't want massive attachments in your emails it is alright to apply strong compression as much as 5 on the jpeg compression scale but when you are sending images to be seen by other photographers you want to be more conservative, somewhere between 8 and 10 on the compression scale seems appropriate. The problem with severe compression is that the data that is discarded results in what can be seen as compression artifacts. Compression artifacts can sometimes be seen as posturising in what should be smooth gradients, 'jaggies' along sharp edges, mosquito noise or blockiness in busy regions. Once your eye tunes into artifacts they are hard to ignore and can distract a viewer of your images.

A straight out of the camera image may be in the order of 7 or more MB. If used for projection purposes this would take interminably long to upload to the screen. What then happens is the judge thinks they have not pressed the forward button on their remote properly so they press it again, then the show jumps forward two places and so they have to press reverse. In general aim for aim for around 1 - 1.5MB though as little as 600KB may often suffice. A few dummy runs at file saving and checking the resultant sizes will give you the clues to the best settings to use.

Save your prepared image files somewhere you will be easily able to find them and, sorry to labour this point, using a new file name. They are now ready to send to the Competition Secretary or to the web site.

NB Some email programs and services will recognize that your attachments are pictures and will offer to "optimize" your images for email delivery; do not allow them to do so as they can ruin all the hard work you just went through to prepare your images for submission. Similarly, some editing programs offer the user the facility to send images via email directly from the tool. Unless they are transparent about what they are doing to the image, especially concerning the physical file size and the amount of compression they will apply to a file, then it is better that you go through the inconvenience of manually resizing your images as described above rather than be disappointed when you see you images projected on the large screen at the club.

This article is reprinted (with some amendmants) by kind permission of the Photochrome Camera Club of San Francisco


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