JPEG Compress
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Jpeg compression allows you to choose whether you prefer a jpeg image file to be large and of high quality
or whether you prefer a smaller file of lower quality.
Jpeg compress your images especially to publish them on the web.
To publish images on the web, some middle course is recommended because big files will take to much time to appear on the surfer's screen.
Compressing a Jpeg does not change the width and the height of your image, only the file size.
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Because YOU choose how small the file will be and you may choose to shrink the image file heftily,
some call compressing Jpegs, crunching Jpeg images or shrinking Jpegs.
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Standard settings
Photo software with standard jpeg compress abilities will let you choose either
a quality factor from 1 to 100. 100 is best quality and biggest file, less than 20 is mostly ugly but files are very small.
or a compression factor from 1 to 100. 1 is best quality and biggest file, more than 60 is mostly ugly but files are very small.
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When you save an image as a jpeg file, the "Save as.." dialog box normally has an option button.
This is where you select the quality factor -resp. the compression factor-. |
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Classification
Many photo editors offer poor jpeg compress abilities, but it may be sufficient for the average user.
I did classify jpeg compression abilities in 4 categories:
The inflexibles
Photo or image editors that do not offer any setting possibility.
Either they save jpeg images with the highest quality factor and you get relatively big files.
Or they did decide to apply a hard-coded quality factor of 90?, 80? or whatever.
They do not tell you and you can not change it. I do not recommend this class of photo editors.
The little flexibles
Photo or image editors that offer let's say 3 predefined settings,
-high, medium and low quality-.
They do not tell you which qualiy factor is applied.
A little bit better than the inflexible ones, but not yet enough for me.
The standard
Most good photo editors will be in this category. They offer settings like defined in the standard settings above.
Either a quality factor where 100 is the best quality or a compression factor where 1 is the best quality.
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Occasionally I did see some photo software whith a quality factor -resp. compression factor-
ranging from 1 to 256 instead of 1 to 100! |
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The better than average
The compression possibilities of jpeg files are huge and in deed you can influence the result with much more parameters,
not only the quality factor
-resp. compression factor- but few programs let you do this!
Advanced Jpeg Compressor is one of the best.
It is not a photo editor, but a specialized software to jpeg compress your photos.
At 1st you may feel overwhelmed by the numerous settings that you can (should) choose.
I would say, don't be afraid. There are 3 things you may consider at first:
- the compression factor for brightness
- the compression factor for color
- the precision factor with 3 possible values, high, standard and low
Forget all the rest at first, until you really feel you need it.
Additional possibilities include selecting an area in your image that will have different compression factors than the rest of your image.
Photo-Brush is a photo editor with better than average jpeg compress abilities.
It has a quality factor ranging from 1 to 100 like many photo editors.
But additionally it has the precision factor mentionned above, with 2 possible values normal and enhanced sampling.
Do not search the option button in the "Save as.." dialog box with
Photo-Brush.
A jpeg compress dialog will automaticaly appear after you click the save button from the "Save as.." dialog.
Examples:
jpeg file
quality = 95
file size = 25 kbytes
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jpeg, zoom = x4
quality = 95
the pixels are clearly visible
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jpeg file
quality = 75
file size = 11 kbytes
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jpeg, zoom = x4
quality = 75
the pixels are clearly visible
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jpeg file
quality = 15
file size = 4 kbytes
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jpeg, zoom = x4
quality = 15
the pixels are clearly visible
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The red area problem
While most photos still look pretty good with a quality factor of 75,
photos with large uniform red areas look quite bad with a quality factor of 85 or even 95 already.
The solution is to use a software that permits to select a better sampling precision,
either high precision with
Advanced Jpeg Compressor
or enhanced sampling with
Photo-Brush.
This way a quality factor of 85 may still be acceptable.
Examples:
normal sampling
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enhanced sampling
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jpeg file
quality = 95
file size = 16 kbytes
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jpeg file
quality = 95
file size = 22 kbytes
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jpeg file
quality = 85
file size = 10 kbytes
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jpeg file
quality = 85
file size = 12 kbytes
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jpeg file
quality = 75
file size = 7 kbytes
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jpeg file
quality = 75
file size = 9 kbytes
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