July 27, 2010

Balancing image quality and SWF output size in CP 5 – 1

Some captions and parts of images might have a dark background when published in CP5 with slide quality set as JPEG. The same project seems to work fine when published with CP4 with the same setting. This is because the mechanism to publish images has changed significantly from CP4 to CP5. In this two part blog series we look at information that you can use in Adobe Captivate 5 to parallel decide the quality of an image and the SWF file size and bring forth the differences between the publishing of images in CP 4 and CP 5.

Size of SWF output files is an important consideration for many content developers as it takes longer time for end users to download larger files. Many factors, such as, recording area, colors in the application that is recorded, FMRs, and background noise contribute to a large output file.

Images are one of the factors that impact the size of a project to a large extent – the higher the quality or the resolution of the image, the larger is the size of the project. Most images appear clearly in the output with low resolution; however, in some cases, your projects may warrant high resolution images. Keeping the file size reasonably low with high resolution images can be quite a challenging task.

Note: General tips to tweak the other factors that affect the file size are at
http://www.adobe.com/devnet/captivate/articles/filesize.html
http://rajntechnlife.wordpress.com/2007/02/16/how-to-reduce-captivate-fileswf-size/

Adobe Captivate 5 lets you choose the level of quality for an image, based on the number of colors and transparency levels you need in the output. These settings can be specified at the slide-level, which makes it convenient for you to have different resolution settings for different images in the project. For example, you may choose to publish the images on the introductory slides with low resolution and those on the core slides with a higher resolution. The different quality levels you can choose for a project are

Low 8 bit – Publishes the images with the smallest size possible. When an image is published as low quality, Captivate tries to determine the optimal 256 colors with which to display a bitmap. This bitmap may contain more than 256 colors.This option works well for most images and for all the screen recorded content, but can fail if the image contains too many colors or many colors with different transparencies. This is usually the case with high fidelity PNGs or imported Photoshop files. JPEG images are still published as JPEG; their compression is controlled by the JPEG quality percentage set in the SWF size and quality preferences.

High 24 bit – Publishes images as bit bitmap images with the highest possible fidelity and no loss of quality. Selecting ‘high’ for all slides results in a large SWF output file. JPEG images are still published as JPEG and their compression is controlled by the JPEG quality percentage set in the SWF size and quality preferences.

Optimized – Publishes all images including JPEG images as high quality bitmap images. This option is similar to ‘high’ . This can drastically increase the file size.

JPEG – JPEG is the jpeg-equivalent of the ‘optimized’ option. This option publishes all images including non-JPEG images as JPEG images. Note that JPEG does not support transparency and transparent images such as PNG images do not appear clearly if published with this option.

In part 2 we will look at the changes from CP4 to CP5 in the way we publish images and how this is causing the dark backgrounds around captions

Posted by gokul3:28 PM
  • Loraine Chant

    I’ve been experimenting with the individual slide quality settings as I was getting really large published file sizes and had been asked by my ICT Manager to have a look at reducing them.

    Interestingly enough, I had many screens with PNG files on them, where i’d isolated out a portion of the image previously in Photoshop (i.e. a cut out photo of a person instead of a rectangular photo of them), and when using the JPEG setting, this isolated cut out effect remained…. I was expecting the PNG to return to a rectangular shape with the isolated portions appearing as a flat or white colour background. This didn’t happen, so the published SWF appeared fine. I could have an isolated shape moving across a patterned background and it still worked fine..! and my published file size has been drastically reduced to boot!

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