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@San Francisco

Sorry, for RGB Pictures, I said 16bits, I checked Photoshop, We are using 24bits.

engmonkey(臭猴子)
本文发表在 rolia.net 枫下论坛For a picture of 1024x683 pixels, we have 8bits per R, G, B chanel which is 24bits per pixel, one byte= 8 bits, so 24 bits=3 bytes= one pixel. 683x1024=699k, 699k pixels x 3 bytes per pixel = 2Mbytes. The best JPG format is 1/4 the size of Bitmap, which means it anyway compresses the file.

So Without compression, a camera of Y Mega pixels will have a file of 3*Y Bitmap file which is RGB format. It gives the Y mage pixels picture a file with size of 3*Y*0.25=0.75*Y bytes.

Raw format, instead of capture 8bits per chanel, 12bitsx 3 chanels are captures, which means 36bits= 4.5bytes = one pixel. Some loss free compression must have applied to the format to explain why instead of a file size 4.5 times the pixels, we usually see equal to the pixels number. The RAW just means no image processing, restrictly speaking, not compressing. Evidence of Raw format is result of compression is: different pictures have different raw file size, the more subtoned the picture is, the smaller the file size, which is the feature of image compression techniques.更多精彩文章及讨论，请光临枫下论坛 rolia.net
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Last Updated: 2006-1-6
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Replies, comments and Discussions:

  • 枫下拾英 / 摄影艺术 / 第一次摆弄数码相机, 有问题请教各位大侠:1)6M的分辨率，照片最大能放大到几寸? 2)照片用photoshop crop了一下，长宽的比例变了，还能不能送出去打印？先谢啦． -roo(不喜欢下雨); 2006-1-2 (#2694073@0)
    • ^ 没人知道吗? -roo(不喜欢下雨); 2006-1-3 (#2696147@0)
      • 1）。 2MP的打印5*7的都没问题。6MP的可以打A4啦！2）。长宽的比例变了，打印出来的质量是不会有问题的。 -kakevin2000(kevin); 2006-1-3 (#2696233@0)
        • 谢谢啦! -roo(不喜欢下雨); 2006-1-3 (#2696342@0)
    • 借光问个菜鸟问题，数码相机拍时设置７M的分辨率，用电脑自带的card reader当到电脑硬盘上，检查照片，就只有３.５Ｍ，这是怎么回事儿？多谢回答。 -table(桌子来了); 2006-1-4 (#2697239@0)
      • 你的3.5M是像素还是文件大小(Byte)?像素大于文件大小 -vicky2005(孩子她爹); 2006-1-4 (#2697249@0)
      • haha@__@菜鸟 -vega_lee(天津包子-就不改); 2006-1-4 (#2697251@0)
      • 7M = 7 million pixels...... -ding_ding(丁_丁); 2006-1-4 {392} (#2697259@0)
        7M = 7 million pixels. If each pixel has 16 bits data (depend on color depth), it will have 7x16 = 112M bits, it's the raw format. After compression, like JPG format, it will reduce the size of file greatly. So you will get a file size about 4M, each one is different, depends on the complexity of the image. Some professonal DSLR will have 36 bits color depth, so generate much larger file.
        • thank you so much for the answer. -table(桌子来了); 2006-1-4 (#2697269@0)
      • Do don't only look at pixels when you buy camera. -ding_ding(丁_丁); 2006-1-4 {477} (#2697326@0)
        Do don't only look at pixels when you buy camera. Some other aspects are more important. 1. color depth, most pocket DC don't say anything about it, maybe there are not that good, (16bits?). I once had a old Kodak professonal DSLR with only 1M pixels but have 36bits color depth, the photo looks much better that what now I have (7M pocket DC). 2. CCD size, for the same pixels, small CCD has poor image quality and lower ISO so poor low light performace. 3. quality of lens.
      • 7mega pixel的相机，存成jpeg格式的应该是3.5Mbytes左右。非常正常，没有问题。 -kakevin2000(kevin); 2006-1-4 (#2697514@0)
      • 专业回答 -engmonkey(臭猴子); 2006-1-5 {418} (#2699833@0)
        7M的相机说明是像素点长x宽约等于7000000。与文件大小不是一回事。一班相机用.jpg格式储存照片，大大压缩了文件尺寸。只有少数有raw格式的相机可以储存未压缩的照片。虽然7M的raw格式文件很接近7M大小，但是这不等于说像素的多少等于文件的大小。一般我们用16bits 格式储存照片，也就是一个像素需要16位0101。。。01来储存。这是恰好是一个字的长度(32bit is double word, 8 bit is a byte). 所以 目前来讲，7M像素的相机的未压缩格式文件才正好是7M.
        • 7M = 7M Word? -kuma(kuma); 2006-1-5 (#2700691@0)
          • Sorry, for RGB Pictures, I said 16bits, I checked Photoshop, We are using 24bits. -engmonkey(臭猴子); 2006-1-6 {1064} (#2701371@0)
            本文发表在 rolia.net 枫下论坛For a picture of 1024x683 pixels, we have 8bits per R, G, B chanel which is 24bits per pixel, one byte= 8 bits, so 24 bits=3 bytes= one pixel. 683x1024=699k, 699k pixels x 3 bytes per pixel = 2Mbytes. The best JPG format is 1/4 the size of Bitmap, which means it anyway compresses the file.

            So Without compression, a camera of Y Mega pixels will have a file of 3*Y Bitmap file which is RGB format. It gives the Y mage pixels picture a file with size of 3*Y*0.25=0.75*Y bytes.

            Raw format, instead of capture 8bits per chanel, 12bitsx 3 chanels are captures, which means 36bits= 4.5bytes = one pixel. Some loss free compression must have applied to the format to explain why instead of a file size 4.5 times the pixels, we usually see equal to the pixels number. The RAW just means no image processing, restrictly speaking, not compressing. Evidence of Raw format is result of compression is: different pictures have different raw file size, the more subtoned the picture is, the smaller the file size, which is the feature of image compression techniques.更多精彩文章及讨论，请光临枫下论坛 rolia.net
    • good for 4x6
      -vipros(vipros); 2006-1-4 (#2698035@0)

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