Category Archives: Packaging Design

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Image resolution for printing – LPI and DPI

A digital “raster” image acquired from a scanner, a digital camera, or created directly in a “paint” application like Adobe Photoshop is made up of a mosaic of “pixels” (picture elements).”

The physical size of the image is described by two numbers which can be expressed two ways:

1) The number of pixels per inch/centimeter.
2) The number of pixels in both horizontal and vertical dimensions.

Or:

1) The number of pixels per inch/centimeter.
2) The horizontal and vertical dimensions expressed in inches/centimeters.

Those are just two ways of saying the same thing.

Note that I use the term “pixels per inch” – ppi. Very often the term that is used is “dots per inch” or dpi. Technically the terms are not interchangeable – however, in daily usage, when speaking about digital images the terms are considered as meaning the same thing. You may sometimes hear the term “spi” – samples per inch. This refers to a scanner’s resolution – i.e. it ability to acquire an image at so many samples per inch (e.g. 300 spi). Again, in practical usage, when speaking about digital images – ppi, dpi, and spi can be understood as meaning the same thing.

Interestingly, digital cameras typically do not have a resolution assigned to them.

Instead a digital camera captures data based on the “megapixel” ability of its CCD sensor. For example, a 14.2 megapixel camera might capture an image that’s 4592 pixels by 3056 pixels, which equals 14,033,152 total pixels. When you open the file into an image-editing program a resolution must be assigned to the file. Most programs, including Photoshop, use 72 ppi as the default resolution.

Background – halftone dots make the image reproduction

Because printing presses can only lay down 100% ink or 0% ink, digital images acquired from scanners, digital cameras, or created directly in “paint” applications need to be converted into a binary (on/off) format. This is done through a process called halftone screening. The result is that the image will be converted to dots of either 100% or 0% ink with the original tones being simulated, in this case, by the size of the dots. Bigger dots represent darker tones – smaller dots represent lighter tones:

The fineness of the screen, and hence the level of detail in the original that can be preserved, is determined by how densely packed the dots are and is indirectly described by how many rows – or linesof dots are used per inch (or centimeter) to create the image. These virtual lines are highlighted in red below:

The key thing to remember is that although the halftone image is made up of dots – the level of detail that it can reproduce is described in terms of lpi NOT dpi.
So, original image pixel density/detail = ppi, spi, or dpi. Halftone reproduction dot density/detail = lpi.


Of course, in order to pack more lines of dots into an inch – the smaller the dots become and hence the greater amount of image detail that is preserved.

The relationship between dpi/ppi and lpi for grayscale images

The guiding principle for understanding what original image resolution (ppi/dpi) is needed compared to the halftone screen (lpi) that will be used is that the image pixels should always be more densely packed (ppi/dpi) than the detail resolving ability (lpi) of the halftone screen that is used.

This minimum required original resolution can be represented by the formula: 1.5 X lpi = ppi @ 100% reproduction.

This ideal required original resolution can be represented by the formula: 2 X lpi = ppi @ 100% reproduction.

The relationship between dpi/ppi and lpi for CMYK images

As with grayscale images, the guiding principle for understanding what original image resolution (ppi/dpi) is needed compared to the halftone screen (lpi) that will be used is that the halftone screen should not reproduce the image pixels themselves but instead the tones the pixels represent. It is worth comparing these images to their grayscale equivalents in part 3.

This minimum required original resolution for a CMYK image can be represented by the formula: lpi = ppi @ 100% reproduction.

This ideal original resolution can be represented by the formula: 1.5 X lpi = ppi @ 100% reproduction.

This maximum required original resolution can be represented by the formula: 2 X lpi = ppi @ 100% reproduction.

The below table provides image resolution requirements for a variety of typical print applications:

Table of resolutions
Image resolution “gotchas” – where things can go wrong

Whether you are targeting your images for AM or FM screening, there are at least three places where the resolution of the images may be accidently altered:

1) If the image is resized/scaled in the page layout application – it may no longer have an appropriate resolution:
2) If the image is resized/scaled when the file is converted to the PDF format – it may no longer have an appropriate resolution:
3) If the printshop’s workflow is setup to resample incoming documents – they may no longer have an appropriate resolution. Most prepress RIPs are set, by default, to downsample incoming files to 300 ppi/dpi.

For more details, check here.

Shanghai DE Printed Box is a China medium-sized custom paper box manufacturer and packaging solution provider with facilities around 100,000 square meters in total. The company exclusively specializes in the supply and export of the custom paper boxes, including the paper printed boxcorrugated printed boxcosmetic paper boxrigid paper box, cardboard gift box and custom paper bag. If you have any questions about the custom paper box, or would like us to give you a price quote, please do not hesitate to contact us by giving us an email.

Paper Box with the Hanger Tab

paper printed box with the hanging hole

In the convenience store, supermarket, a beautifully printed paper box with a hanger tab (the paper box on the left) is too striking to escape the consumers’ eye. And the products packed within sell fast.  Why?

The hanger tab does the tricks. With the hanger tab, the product is hanged at the best visual position and is seen easily. And the front side, left side and right side of the packaging box is in the visual field of the consumers.

The color box on the left  is produced for Rapid Ramen Cooker. You can see this brand easily in Walmart, Amazon. It is made of 350gsm duplex board with grey back (also referred to as 20pt CCGB).  The box structure is tuck top auto bottom (also referred to as TTAB) with the hanger tab. It has the CMYK full color printing. The UV glossy finish on the surface gives it a glossy and smooth feel and make people want to eat when seeing it.

artwork for the TTAB box with hanger tab

Shanghai DE Printed Box is a China medium-sized custom paper box manufacturer and packaging solution provider with facilities around 100,000 square meters in total. The company exclusively specializes in the supply and export of the custom paper boxes, including the paper printed boxcorrugated printed boxcosmetic paper boxrigid paper box, cardboard gift box and custom paper bag. If you have any questions about the custom paper box, or would like us to give you a price quote, please do not hesitate to contact us by giving us an email.

The difference of the A series paper in China

The dimensions of the A series paper sizes are defined by the ISO 216 standard. And it is widely adopted by the countries in Europe and North America. However, things are quite different in China. For example, the international standard A4 paper size is 210*297mm, while it is 210*285mm in China.

Due to the low costs of printing and packaging in China, many European and North American Countries import printing and packaging products from China. Therefore, for the graphic designers, a good understanding of the paper size used in China can efficiently reduce the paper cutting waste and cost. Below are the details.

A paper size

所谓A4的纸张就是A系列幅面的纸张的十六分之一大小
我们常用的纸张有A、B系列的幅面
拿A系列的纸张来说:A0是全开的,A1是对开的,A2是四开的,依次类推……A系列开度是国际标准开度,如:A0是全张纸,它正16开的结果是A4(210mm*297mm),相对应:
有我国的国内常用纸开度,如:787mm*1092mm是全张纸,它的16开是185mm*260mm
889mm*1194mm是大全张纸,它的(大)16开是210mm*285mm

A为1000*1400
B为1200*1600

纸张尺寸一览表
开本按照尺寸的大小,通常分三种类型:大型开本、中型开本和小型开本。以787×1092的纸来说,12开以上为大型开本,16~36开为中型开本,40开以下为小型开本,但以文字为主的书籍一般为中型开本。开本形状除6开、12开、20开、24开、40开近似正方形外,其余均为比例不等的长方形,分别适用于性质和用途不同的各类书籍。
正度纸张:787×1092mm
开数(正) 尺寸 单位(mm)
2开  540×780
3开  360×780
4开  390×543
6开  360×390
8开  270×390
16开  195×270
32开  195×135
64开  135×95
注:成品尺寸=纸张尺寸-修边尺寸

大度纸张:889*1194mm
开数(大) 尺寸 单位(mm)
2开 590×880
3开 395×880
4开 440×590
6开 395×440
8开 295×440
16开 220×295
32开 220×145
64开 110×145
注:成品尺寸=纸张尺寸-修边尺寸

补充:
A4  210mm×297mm

B5 182mm×257mm

16K 193mm×270mm

A3  297mm×420mm

B4  257mm×364mm

8K  270mm×386mm

印刷品成品尺寸
大度
2开 870×570
3开 390×870 420×580
4开 420×580 290×870
8开 420×285 210×570
16开 210×285
32开 210×140 105×285
48开折页 95×210
48开 92×210
正度
2开 760×520
3开 350×760 360×680
4开 370×520 260×760
8开 185×520 370×260
16开 185×260
32开 185×130 92×260

48开折页 86×185
48开 83×185

Shanghai DE Printed Box is a China medium-sized custom paper box manufacturer and packaging solution provider with facilities around 100,000 square meters in total. The company exclusively specializes in the supply and export of the custom paper boxes, including the paper printed boxcorrugated printed boxcosmetic paper boxrigid paper box, cardboard gift box and custom paper bag. If you have any questions about the custom paper box, or would like us to give you a price quote, please do not hesitate to contact us by giving us an email.