The resolution of the inkjet printer affects the detail of the photo and is usually measured in DPI (dots per inch), e.g., a 4800×1200 DPI model is able to atomize 5.76 million ink drops (4 picolitres in diameter) per square inch. Compared to the 1200×600 DPI entry level model (720,000 drops), the detail reduction capacity is 700% greater, and hair (about 0.05 mm in diameter) or cloth texture (less than 0.1 mm in line spacing) can be easily demonstrated. According to a 2022 report by the Rochester Institute of Technology, if the resolution is raised from 2400 DPI to 9600 DPI, the difference in sharpness perceived by the human eye reduces the error rate by 45% at 30 cm of viewing distance, but the marginal benefit reduces – after 4800 DPI, the error rate reduces. Each 10% resolution increase contributed just 2% visual satisfaction (test sample: 50 A4 portraits).
Color transition accuracy bears a close connection to resolution, such as the Epson SureColor P900 (5760×1440 DPI), which uses patented “micro-voltage control technology” to control cyan and magenta titration error at ±5 microns. Enlarge the tone level of skin tone gradations (e.g., RGB 255,205,150 to 255,175,100) from 64 to 256 (step color difference ΔE<1.5), and the blotching of colors due to the diffusion of ink drops in lower end models (e.g. HP DeskJet 2755, 1200×1200 DPI), The same area can display a maximum of only 32 levels (ΔE>3). 6×4 inch prints of the high-resolution inkjet model have 98% color gamut coverage (Adobe RGB) recognized by Pantone, up from 78% in standard models by 25%. In particular, saturation deviation is reduced by 60% in red (620-750 nm wavelength) and blue (450-495 nm) bands.
Print speed goes inversely with resolution, e.g., Canon PIXMA PRO-100 (4800×2400 DPI) prints an A4 HD photo (20,000 drops per second) within 4 minutes and 30 seconds, but can be reduced to 1 minute and 10 seconds in 1200×600 DPI. But concurrently, the noise level increases by 300% (ISO/IEC 24712 test standard). Apart from this, the ink consumption when printing in high resolution mode is significantly greater, taking HP PageWide Pro 477dw as an example, 9600 DPI printing full format photographs needs to consume 1.2 ml CMYK ink (cost around HK $8), while 600 DPI mode only consumes 0.3 ml (cost 2 yuan). But the latter shall be pixelated mosaics once 200% enlarged (single color blocks with sizes of up to 0.1×0.1mm).
Environmental conditions further affect resolution performance, such as Epson PrecisionCore spray heads’ drop accuracy deviation (minimum 3 µl ink drop) up to ±15 microns (±5 microns in dry conditions) in humidity environments of greater than 70%, resulting in a fog haze (0.3 Dmax density deviation) in highly lighted areas such as snowscapes. According to Consumer Reports in 2023, with the conditions of printing by an inkjet printer and RC paper (270g/m² weight), 9600 DPI output photos have only a 5% color degradation rate (ISO 18909 standard) after an accelerated aging test (85°C, 85% relative humidity, 500 hours). However, the same condition sample attenuation rate of low resolution (1200 DPI) output was as high as 22%, mostly due to insufficient droplet penetration depth (just 8 microns instead of 20 microns).
Cost-benefit analysis shows that commercial inkjet printers such as Epson SureColor P7000, which costs HK $28,000, cost about HK $15 per A3+ photo output (paper and ink), and the resolution is increased to 5760×1440 DPI. It is able to achieve the commercial copy shop industry standard of 0.5 pairs of wire per square millimeter (ISO 14604-2), whereas home model with the same specification (e.g., Brother INKvestment MFC-J995DW, priced at HK $2,500) costs HK $5 less. Resolution limitations, however, make the output impossible to be Fogra certified (color tolerance ΔE>5). According to the NPD Group, the global high-resolution inkjet printer market will grow by 17% in 2022, and 72% of demand for purchases comes from photography studios and art print centers mainly due to the success of 4K/8K display devices. Consumer demand for output accuracy has enhanced (60% of consumers require that the pixel-level matching error between the screen display and printed photo be less than ±2%).