Legacy ImageMagick Discussions Archive

Large : https://s3-us-west-2.amazonaws.com/qiniu-bs/97kb.jpeg
Small : https://s3-us-west-2.amazonaws.com/qiniu-bs/90kb.jpeg


Two images look like the same ,and quality is the same.
I want know how to reduce the large image size to 90kb,and width, height and quality no change

Quality is 100 in both images, but JPEG quality 100 is not lossless. The images are slightly (but imperceptibly) different. Compress them again with quality 92, they still look the same but are less than half the size. Compress them with -quality 75 and they still look the same but are reduced again by about 50 percent. It's not useful to compress JPEG images with a higher quality than what came from the camera, which is generally 85-95.

glennrp wrote:Quality is 100 in both images, but JPEG quality 100 is not lossless. The images are slightly (but imperceptibly) different. Compress them again with quality 92, they still look the same but are less than half the size. Compress them with -quality 75 and they still look the same but are reduced again by about 50 percent. It's not useful to compress JPEG images with a higher quality than what came from the camera, which is generally 85-95.

Sorry, maybe you don't understand my question，it's my problem
I don't want reduce quality (i know reduce quality can reduce image size).

OK,now i have two questions
1、why the small picture size less than the large one.
2、 largest : https://s3-us-west-2.amazonaws.com/qiniu-bs/104.jpeg
The difference between largest and large is the option 'interlace',but 'interlace' only change (RGBRGB...) to （RR...GG..BB..）not compress,and others picture no change after add 'interlace'.
Can you tell me why

1. The 90kb picture size is less than the larger ones because they are slightly (but imperceptibly) different. It is more compressible than the others. The 97kb and 104kb images have identical pixels.

2. As you observed, the 97kb is interlaced and the 104kb isn't. The order in which numbers appear in a datastream can affect its compressibility.

glennrp wrote:1. The 90kb picture size is less than the larger ones because they are slightly (but imperceptibly) different. It is more compressible than the others. The 97kb and 104kb images have identical pixels.

2. As you observed, the 97kb is interlaced and the 104kb isn't. The order in which numbers appear in a datastream can affect its compressibility.

How to change 97kb picture to 90kb,i know they are slightly different.Can you be more specific

needkane wrote: How to change 97kb picture to 90kb,i know they are slightly different.Can you be more specific

Reduce the quality to 99. But you don't want to do that, so I have no answer for you other than to repeat that the 90kb and 97kb images are of slightly different quality, even though you requested quality 100 for both.