jpg images converted to PNG with wand get much larger

Question

I've got a batch process that converts uploaded images using wand to generate thumbnails and resized versions. The problem is that the converted images get a lot larger than the original image. An uploaded jpg (1024x768) that was 239kB ends up over 1.2MB at 800x600. If I just resize but don't change format, the image is 132kB. Here's the relevent bit of code from my script.

im1 = Image(blob=file) sizemedium = '800x600' im1.transform(resize=sizemedium) im1.format ='png' medfile = im1.make_blob()

Larger file size is to be expected when converting a JPG to a PNG. — user13286, Apr 08 '14 at 20:10

score 2 · Accepted Answer · answered Apr 08 '14 at 20:10

Keep the format. PNG uses a different way of "encoding" color and is not very optimized for photos (it is better for illustrations, icons and clip art).

You'll see it works fine if there is a limited number of colors in the image.

Rule-of-thumb for image formats is to use JPEG for photos, PNG for anything else.

score 0 · Answer 2 · answered Apr 08 '14 at 20:12

0

The thing is that PNGs can be larger than JPGs, specially when you are storing photos, so that might be the problem. If you do not need a PNG for a specific reason I would just keep the JPG format.

answered Apr 08 '14 at 20:12

cnluzon

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jpg images converted to PNG with wand get much larger

2 Answers2