Image Compression and How it Affects Picture Quality
We have had a lot of requests over the last year and a half concerning image submissions and what is the best way to submit them. I am going to go over the several different ways an image can be saved in this article to give everyone a good idea of what makes a good online image. As well as what images don't.
You have just photographed your model using your digital camera and are so happy with the results (hey it even captured that weathering effect!) that you want to share them with the world. And why not. We all love to come here and see others work whether great or small (like Braille scale) it can be a great source of inspiration to us modelers. So you used the default image size on your camera (let's say 640 x 480 pixels) and you have your JPG or TIF images ready to send via email. For many of you this can be the end of this article. If the images aren't too large an upload for you or your hosting situation (some ISPs have a 5mb or other limit on email attachments) you can just zip them up and send them to us. If however you want to re-size or re-save/compress your images to a more manageable level, read-on.
Digital cameras have various quality levels for shooting images. This usually is translated to some consumer nomenclature like HQ (high-quality), SHQ (super-high-quality), and the like. What this really translates to is image size (in pixels) and compression rates. If you camera mode is outputting a TIF file as the final image file then your images are un-compressed (more than likely). Compression is the process of removing similar colors to reduce the file size. For example a TIF file could be as large as 5mb (5+ million bytes) and be resized and re-compressed into a JPG that would be only 50kb (50,000+ bytes). Amazing eh? So, your camera mode will have a lot to do with whether you can simply download your images from your camera and zip and email them online. There are other options for sending us images of course. Contributors can physically mail us images on a CD-ROM disc via our mailing address.
Best Image Size
Generally we would like to do all the major image re-processing unless you consider yourself very skilled with Photoshop or another good image editing tool. I have seen many examples of great model pictures that were either mangled in the process of submitting them (made too small, cropped badly, color/brightness levels bad, etc.) so we prefer just getting as large an image as you/we can safely get via email or regular mail. Generally speaking for the web we will not display an image larger than 800 pixels wide. Almost 95% of our images are less than 600 pixels in width. But again this does not mean you need to re-size the images yourself to 600 x 450 pixels. If your images are 1280 x 768 pixels that is fine. The issue you may run into (as described above) is that the image file size is too large for easy sending via email. To solve this dilemma you just need to open your images in Photoshop or another "compression capable" image editor and re-save them with additional compression. I have used the example images here to illustrate exactly what happens when you change the compression on an image. This image is the 600 X 450 size we generally use on the site, but keep in mind this image could have just as easily been the 1280 X 768 raw image from my digital camera (it just would have gone off the side of the screen).
The Raw Image - 600 x 400 pixels - 296 kb
This images had ZERO additional compression. I took my original RAW image and re-sized it for this example down to 600 x 450. Then I used the standard "save-as" function in Photoshop and select JPG and maximum as the compression level. This created the image as a 296 kb (kilo-byte) image. This image would be fine to submit as is (unless you had many images like this and cumulatively they caused a problem to send).
Maximum Setting - 600 x 400 pixels - 104 kb
This image was made using the above image and the "Save for Web" feature in Photoshop. This is a special function in Photoshop that makes a "web-ready" image that is as small as possible. This image was saved again using the maximum setting (meaning maximum image quality or almost zero compression). You will probably note right away that there is NO VISIBLE DIFFERENCE between this image and the one above even though this one is almost 1/3 the file size. This image would be perfect for submission as is.
High Setting - 600 x 400 pixels - 60 kb
This image was saved again using the high setting in the "Save for Web" feature in Photoshop. You will probably note again that there is NO VISIBLE DIFFERENCE between any of the images above. This image would be perfect for submission as is.
Medium Setting - 600 x 400 pixels - 32 kb
This image was saved again using the medium setting in the "Save for Web" feature in Photoshop. This image came out very well and would be acceptable for publishing as-is. However this may not always be the case. Most of my images for example are either saved as medium or high settings.
Low Setting - 600 x 400 pixels - 20 kb
This image was saved again using the low setting in the "Save for Web" feature in Photoshop. You will probably start to see some major image differences with this image versus the ones above. Generally over-compressed images start to get a "blurry" quality to them. This makes sense because the compression feature is trying to blend things together. This image would not be the preferred quality for the site. We might still publish this image if the subject material was of high-value, but would probably request you send us better images.
Great. But I don't have Photoshop so what do I do?
Look closely when you are in the save area of your photo editing program. Hopefully you will see some setting that will allow you to change the compression level of your JPG images. If you don't then just resize your images to 600 x 450 and hopefully that will lower the file size to an acceptable level. If you have the funds you can also look into getting Photoshop Elements. This is a non-professional version of the popular software and it has the Save-for-Web function as well as Auto Levels, Un-sharp Mask and other good editing features I sometimes refer to.
I hope you have found this helpful. Remember you can always post image related issues, suggestions, or requests in our Photgraphy & Digital Photo Editing Forum.