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Visio 2010 - Compression of Photos inside of Visio - How much?

Is there a calculation I can use to determine how much I should compress my photos?  I don't know how much to slide that "hi quality/lo quality"  control to the left   But I do know that each of my photos in JPEG format is 1.8 Meg each.  So there is some room for improvement.  These are data center photos.
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brothertruffle880
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brothertruffle880
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Eoin OSullivanConsultantCommented:
JPEG is a lossy compression format best suited to photographs and images with plenty of detail and texture.  The more you compress the more artefacts and visual distortion you get in the image.
There is no absolute guide as each image will compress slightly differently depending on the ability of the JPEG algorithm to process the photo.
JPEG is not good at compressing vector artwork, diagrams or illustrations as the flat colours and straight lines present less chances for the compression algorithm to replace the original pixels with fractal patterns.
The two factors that determine the filesize will be the overall resolution of the image (height and width in pixels) and the level of compression.  
A JPEG of 1.8Mb is either very large in pixels (2000x2000 or bigger) and has very little compression and is still at high quality.
Different applications give you different dialogs to set the compression level of JPEG but a simple rule is that 100% is full resolution, lossless compression and 20% would be high level of compression with very obvious artefacts and a much reduced image quality.
Normal photos can be reduced to 60-80% of original quality with little visual artefacts or image quality loss.  Dropping below 60% you will still recognise the image but will definitely see some small areas of blurring or distortion.  Drop below 40% and the artefacts increase etc.

The only hard and fast rule is .. test and see.  If the compression of 50% is acceptable then go with that but remember that every photo will vary to some extent so test several images to see if they average image loss is agreeable.
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Darr247Commented:
Try saving them as Portable Network Graphics (.PNG) format instead... that uses lossless compression.

Compression Factors of more than 10 to 15 (the graphics programs I'm familiar with use a scale of 1 to 99 to quantify the amount of JPG compression, and do not call it %) produce visible artifacts along borders of objects and text, in my experience.

Compare the size and quality of these screengrabs of a microsoft dialog... by the time the JPG files get smaller than the PNG file, artifacts between the lines of text are clearly visible.
Unsigned Program Warning - PNG formatUnsigned Program Warning - JPG format - Compression Factor 10Unsigned Program Warning - JPG format - Compression Factor 20Unsigned Program Warning - JPG format - Compression Factor 30Unsigned Program Warning - JPG format - Compression Factor 40
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